Time-course transcriptomics analysis reveals key responses ...€¦ · energy and then resume...
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Time-course transcriptomics analysis reveals key responses of 2
submerged deepwater rice to flooding 3
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Short title: Transcriptomics of deepwater rice 6
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All author names and affiliations 8
Anzu Minami1, Kenji Yano1, Rico Gamuyao1, Keisuke Nagai1, Takeshi Kuroha1, Madoka 9
Ayano1, Masanari Nakamori1, Masaya Koike1, Yuma Kondo1, Yoko Niimi1, Keiko 10
Kuwata2, Takamasa Suzuki3,4, Tetsuya Higashiyama3,4,5, Yumiko Takebayashi6, Mikiko 11
Kojima6, Hitoshi Sakakibara 6, 7, Atsushi Toyoda8, Asao Fujiyama8, Nori Kurata9, 12
Motoyuki Ashikari1 and Stefan Reuscher1 13
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1 Bioscience and Biotechnology Center, Nagoya University, Furo-cho, Chikusa-ku, 15
Nagoya, Aichi 464-8601, Japan 16
2 Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo-cho, 17
Chikusa-ku, Nagoya, Aichi 464-8602, Japan 18
3 Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 19
464-8602, Japan 20
4 ERATO Higashiyama Live-Holonics Project, Nagoya University, Furo-cho, Chikusa-ku, 21
Nagoya, Aichi 464-8602, Japan 22
5 Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo-cho, 23
Chikusa-ku, Nagoya 464-8601, Japan 24
Plant Physiology Preview. Published on February 23, 2018, as DOI:10.1104/pp.17.00858
Copyright 2018 by the American Society of Plant Biologists
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6 RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi-ku, 25
Yokohama, 230-0045, Japan 26
7 Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-27
ku, Nagoya, Aichi 464-8601, Japan 28
8 Center for Information Biology, National Institute of Genetics, Mishima, 411-8540, 29
Japan 30
9 Genetic Strains Research Center, National Institute of Genetics, Mishima, 411-8540, 31
Japan 32
Corresponding authors’ details 33
Anzu Minami: Bioscience and Biotechnology Center, Nagoya University, Furo-cho, 34
Chikusa-ku, Nagoya, Aichi 464-8601, Japan 35
Stefan Reuscher: Bioscience and Biotechnology Center, Nagoya University, Furo-cho, 36
Chikusa-ku, Nagoya, Aichi 464-8601, Japan 37
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One sentence summary 39
Comparative transcriptomics and targeted analyses provide insights into the roles of 40
phytohormone synthesis, signaling and turnover during submergence-induced internode 41
elongation in deepwater rice. 42
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Author contributions 44
A.M., M.ASHIKARI and S.R. designed this work and wrote the manuscript. A.M. 45
prepared all plant materials, made cDNA libraries and performed physiological 46
experiments. A.M., K.N., T.K., M.AYANO, M.N, M.KOIKE, Y.K. and Y.N. isolated RNA. 47
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T.S. and T.H. performed transcriptome sequencing and S.R. analyzed the data. A.M. 48
and K.Y. performed additional data analysis. A.T., A.F. and N.K. provided C9285 49
genomic sequence data and S.R performed C9285 genome targeted de novo assembly. 50
K.Y. performed promoter element enrichment analysis. K.K. carried out proteomics 51
analysis. Y.T., M.KOJIMA. and H.S. analyzed hormone concentrations. R.G. provided 52
many critical suggestions, did final editing and proofreading of the manuscript. 53
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Funding information 55
This work was supported by JST Core Research for Evolutional Science and 56
Technology, a MEXT Grant-in-Aid for Scientific Research on Innovative Areas 57
(22119007 and 17H06473) and JICA-JST SATREPS, by JSPS Grand-in Aid for Young 58
Scientists (B) Grant Number 17K15136 to A.M. and by a JST ERATO Grant 59
(JPMJER1004) to T.H. 60
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Present addresses 63
Kenji Yano: Faculty of Agriculture, Tokyo University, 1-1-1 Yayoi, Bunkyo, 113-8657 64
Tokyo, Japan 65
Rico Gamuyao: Department of Ophthalmology, Johns Hopkins University School of 66
Medicine, Baltimore, MD 21287, USA 67
Takeshi Kuroha: Department of Developmental Biology and Neurosciences, Graduate 68
School of Life Sciences, Tohoku University, Sendai 980-8578, Japan 69
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Takamasa Suzuki: College of Bioscience and Biotechnology, Chubu University, 70
Matsumoto-cho, Kasugai, Aichi, 478-8501, Japan 71
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Corresponding author email 73
Anzu Minami: [email protected] 74
Stefan Reuscher: [email protected] 75
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ABSTRACT 78 79
Water submergence is an environmental factor that limits plant growth and survival. 80
Deepwater rice (Oryza sativa) adapts to submergence by rapidly elongating its 81
internodes and thereby maintaining its leaves above the water surface. We performed a 82
comparative RNA sequencing transcriptome analysis of the shoot base region, including 83
basal nodes, internodes and shoot apices of seedlings at two developmental stages 84
from two varieties with contrasting deepwater growth responses. A transcriptomic 85
comparison between deepwater rice C9285 and non-deepwater rice Taichung 65 86
revealed both similar and differential expression patterns between the two genotypes 87
during submergence. The expression of genes related to gibberellin biosynthesis, 88
trehalose biosynthesis, anaerobic fermentation, cell wall modification and transcription 89
factors that include ethylene-responsive factors was significantly different between the 90
varieties. Interestingly, in both varieties the jasmonic acid content at the shoot base 91
decreased during submergence, while exogenous jasmonic acid inhibited 92
submergence-induced internode elongation in C9285, suggesting that jasmonic acid 93
plays a role in the submergence response of rice. Furthermore, a targeted de novo 94
transcript assembly revealed transcripts that were specific to C9285, including 95
submergence-induced biotic stress-related genes. Our multifaceted transcriptome 96
approach using the rice shoot base region illustrates a differential response to 97
submergence between deepwater and non-deepwater rice. Jasmonic acid metabolism 98
appears to participate in the submergence-mediated internode elongation response of 99
deepwater rice. 100
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INTRODUCTION 102
103 Submergence stress is harmful to plants. In addition to causing O2- and CO2-deficient 104
conditions by restricting environmental gas exchange, submergence reduces the light 105
available for photosynthesis, perturbs cellular energy generation and disrupts ionic 106
balance (Bailey-Serres and Voesenek, 2008; Bailey-Serres and Voesenek; Voesenek 107
and Bailey-Serres, 2015). The mechanism of the submergence response has been well-108
studied using rice (Oryza sativa), two diverging Rumex species (R. acetosa and R. 109
palustris) and Arabidopsis thaliana, and several global analyses using transcriptomic or 110
metabolomic approaches to examine submergence or hypoxia/anoxia stress have been 111
reported (Lasanthi-Kudahettige et al., 2007; Magneschi and Perata, 2009; Narsai et al., 112
2009; Mustroph et al. 2009, 2010; Lakshmanan et al., 2013; van Veen et al., 2013; 113
Narsai et al., 2015; Rivera-Contreras et al., 2016). 114
Rice is the most important staple crop in Asia and water availability is a crucial 115
factor for rice cultivation. In tropical Southeast Asia, rice is produced in paddy fields with 116
water-controlling irrigation systems using rivers, lakes, ponds and swamps. However, in 117
some parts of South and Southeast Asia, such as Bangladesh, India, Thailand, Vietnam, 118
and Cambodia, the paddy fields are frequently submerged during the rainy season. The 119
general cultivated rice cannot survive in these submergence-prone areas, but some 120
cultivars such as floating or deepwater rice can grow and survive in such conditions 121
even under several month-long periods of deep flooding. 122
The adaptation of plants to submergence stress involves two different opposing 123
mechanisms, the ‘quiescence strategy (e.g. Rice SUB1 varieties, Arabidopsis ecotypes, 124
Rumex acetosa)’ and ‘escape strategy (e.g. deepwater/floating rice varieties, Rumex 125
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palustris)’ (Jackson, 2008; Bailey-Serres et al. 2012; Loreti et al., 2016). Submergence-126
tolerant rice such as FR13A survives flooded conditions for a few weeks through the 127
‘quiescence strategy’ wherein the plants temporarily cease shoot elongation to conserve 128
energy and then resume growth when the water recedes. Quantitative trait loci (QTL) 129
mapping revealed that the SUBMERGENCE1 (SUB1) locus regulates the ‘quiescence 130
strategy’ (Xu et al., 2006; Fukao et al., 2006). The SUB1 locus on chromosome 9 131
contains a cluster of three group VII ethylene response factor (ERF) genes (SUB1A, 132
SUB1B and SUB1C) and the presence of the SUB1A-1 allele restricts underwater shoot 133
growth and confers submergence tolerance. SUB1A-1 suppresses ethylene production, 134
leading to the suppression of gibberellin (GA) synthesis and GA responsiveness 135
mediated by the negative regulators in GA signaling, SLENDER RICE-1 (SLR1) and 136
SLR like-1 (SLRL1) (Fukao et al., 2006; Fukao and Bailey-Serres, 2008). Moreover, 137
SUB1A-1 activates the expression of various genes, including other ERF genes and 138
genes encoding transcription factors, reactive oxygen species scavengers, and 139
enzymes involved in brassinosteroid synthesis and several metabolic pathways 140
facilitating survival during the quiescent period (Fukao et al., 2006, Fukao et al., 2011; 141
Jung et al., 2010; Schmitz et al., 2013; Tamang and Fukao, 2015). 142
Conversely, the ‘escape strategy’ involves stem elongation to keep the leaves 143
above the water surface. This typically involves metabolic activation and the 144
mobilization of energy reserves to drive elongation growth (Figure 1A). Utilizing this 145
strategy, deepwater rice rapidly elongates its internodes (~20 to 25 cm per day) and 146
reaches a length of several meters in deep water (Catling, 1992; Kende et al., 1998). 147
The deepwater rice cultivar C9285 from Bangladesh belongs to the Japonica varietal 148
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group (Wang et al. 2013) and shows strong internode elongation in response to 149
submergence (Hattori et al., 2009). Our previous QTL mapping showed that the 150
submergence-induced elongation in C9285 is caused by three major QTLs located on 151
chromosomes 1, 3 and 12 and two minor QTL on chromosome 2 and 4 (Hattori et al., 152
2009, Nagai et al. 2012). The major QTL on chromosome 12 contains the two ERF 153
family genes named SNORKEL1 and SNORKEL2 (SK1/2) which are positive regulators 154
of internode elongation. During submergence, the gaseous hormone ethylene 155
accumulates, triggering SK1/2 gene expression in C9285. Although the downstream 156
factors directly regulated by SK1/2 are still unknown, it is clearly established that 157
internode elongation in deepwater rice requires active GA biosynthesis (Ayano et al, 158
2014; Nagai et al., 2014). 159
Both the underwater ‘quiescence strategy’ and ‘escape strategy’ involve ethylene 160
signaling and regulation by strategy-specific group VII ERFs (ERF-VII): SUB1A limits 161
stem elongation underwater whereas SK1/2 promotes the submergence-induced 162
elongation. The molecular mechanisms of SUB1A-mediated ‘quiescence strategy’ have 163
been well-studied (Bailey-Serres, 2010; Voesenek and Bailey-Serres, 2015) and SUB1-164
related gene expression profiles during submergence have been analyzed (Jung et al., 165
2010, Fukao et al., 2011). However, there is little information about the responses of 166
deepwater rice under the ‘escape strategy’. In this study, we explored the transcriptional 167
responses to submergence of the deepwater rice cultivar C9285. We aimed to compare 168
the transcriptional responses associated with phytohormone signaling, regulation of 169
gene expression and energy metabolism following submergence of two contrasting rice 170
varieties (deepwater and non-deepwater rice) at different leaf developmental stages to 171
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better understand the mechanism involved in the ‘escape strategy’. Our findings expose 172
temporal and genotype-specific responses to submergence and implicate a role for 173
jasmonic acid (JA) catabolism in the pronounced submergence-induced internode 174
elongation of deepwater rice. 175
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RESULTS 177
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Transcriptome profiles of deepwater rice and non-deepwater rice plants exposed 179
to submergence 180
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To investigate the gene expression dynamics of deepwater rice in response to 182
submergence, we compared the transcriptome profiles between the deepwater rice 183
Oryza sativa cv. C9285 and non-deepwater rice Oryza sativa cv. Taichung 65 (T65) 184
(Supplemental Figure 1). The internodes of C9285 plants can elongate in response to 185
submergence once plants reach the the six-leaf stage (6LS) (Ayano et al., 2014). 186
Hence for the transcriptome analysis, C9285 and T65 plants at the 6LS were used for 187
expression profiling. We also included submerged C9285 plants at the four-leaf stage 188
(4LS), which cannot respond to submergence by elongation yet. The plants were 189
completely submerged for 0, 1, 3, 6, 12 and 24 hours (h) and we sampled the shoot 190
base region of the stem, as this region in C9285 plants rapidly elongates in response to 191
submergence. Per sample, on average 8.04 x 106 single-end reads were generated, of 192
which an average of 6.83 x 106 reads could be mapped to the transcripts annotated in 193
the Oryza sativa L. ssp. Japonica cv. Nipponbare reference genome (Kawahara et al., 194
2013). The average rates of mapped reads for C9285 and T65 samples in the 195
Nipponbare reference genome were 84.8% and 86.1%, respectively (Supplemental 196
Table 1). After quality control and filtering, we detected 27,812 expressed genes in at 197
least one sample (Supplemental Data Set 1). 198
For global comparison of the transcriptomes derived from all 18 tissue 199
samples, we performed a principal component analysis (PCA). The first two principal 200
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components (PC1 and PC2) accounted for 48% of the total variance (Figure 1B). PC1 201
accounted for 26% of all variance in the data and clearly separated the T65 samples 202
(T65 6LS) from the C9285 samples at two different stages (C9285 4LS and C9285 203
6LS). Among the T65 6LS samples, only the sample from the 24 h submergence 204
treatment showed lower PC1 values closer to the C9285 samples. PC2 (accounting for 205
22% of all variance) separated the samples based on duration of submergence 206
treatment. That is, each genotype showed higher and lower PC2 values reflecting the 207
samples submerged for shorter and longer periods, respectively. The results from the 208
PCA analysis suggest that there are different gene expression patterns between the two 209
rice genotypes dependent and independent of submergence treatment. Furthermore, 210
the expression profiles become variable depending on the duration of submergence 211
treatment but were less affected by the leaf developmental stage in C9285 plants. In 212
addition, a more targeted attempt at isolating genes specifically induced by 213
submergence at the 4LS, but not at the 6LS in C9285 plants found only 36 such genes 214
(see Supplemental Results) 215
Submergence induced expression changes for a large number of genes in 216
both genotypes (Supplemental Table 2 and Supplemental Figure 2A and 2B). To group 217
genes with similar expression profiles, we performed k-means clustering of all 27,812 218
expressed genes. We empirically chose k = 40 for k-means clusters and manually 219
grouped the clusters into four major groups; (1) higher expression in C9285 plants 220
(1,019 genes) (Supplemental Data Set 2), (2) higher expression in T65 plants (1,205 221
genes) (Supplemental Data Set 3), (3) induced expression in both C9285 and T65 222
plants (2,683 genes), and (4) repressed expression in both C9285 and T65 plants 223
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(4,125 genes), excluding clusters which contained genes with no discernable pattern of 224
expression (Figure 2A). In addition, to achieve a better separation of submergence-225
responsive genes, we next performed k-means clustering (k = 20) for each genotype 226
separately (Supplemental Data Sets 4 to 7). In C9285 samples, five (B6, B9, B11, B12 227
and B16) and four (B7, B8, B15 and B17) clusters contained submergence-induced and 228
-repressed genes, respectively (Figure 2B). A total of 2,429 genes in B6, B12 and B16 229
clusters showed the strongest expression around 12 h submergence and a total of 775 230
early responsive genes were classified into B9 and B11 clusters. In T65 samples, five 231
clusters (C1, C3, C5, C13 and C17) contained a total of 4,563 submergence-induced 232
genes and most of the genes showed relatively slow response to submergence except 233
for the 374 early responsive genes in C5 and C17 clusters (Figure 2C). In cluster C2, 234
the expression of 514 genes in T65 plants was repressed by submergence. We 235
evaluated the biological function of genes enriched in each group of clusters based on 236
the MAPMAN ontology (Thimm et al., 2004; 237
http://mapman.gabipd.org/web/guest/mapman). The hierarchical enrichment analysis of 238
MAPMAN bins of genes with higher expression in C9285 or T65 plants (P < 0.05) and 239
the data of submergence-changed genes in C9285 or T65 plants (P < 0.05) are shown 240
in Supplemental Table 3 and Supplemental Table 4, respectively (described in 241
Supplemental Results). Selected enriched MAPMAN bins were then chosen for further 242
analysis. 243
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Different expression pattern of genes related to plant hormone biosynthesis 245
during submergence in both genotypes 246
247
Kende et al. (1998) proposed a model describing the relationship among the three 248
phytohormones ethylene, abscisic acid (ABA) and gibberellin (GA) in regulating rapid 249
internode elongation of deepwater rice. During submergence, the reduced diffusion of 250
ethylene causes its accumulation, which then triggers the ethylene signaling cascade, 251
leading to the reduction of ABA content and increase of GA content (Kende et al., 1998; 252
Fukao and Bailey-Serres, 2008). To investigate the genes related with hormone 253
biosynthesis that are regulated during submergence, we compared the expression level 254
of hormone biosynthetic genes between C9285 and T65 plants. 255
Ethylene is produced from its precursor, S-adenosylmethionine (SAM) derived 256
from the Yang cycle through two steps (Yang and Hoffman, 1984; Wang et al., 2002). 257
The first step is catalyzed by ACC synthase (ACS) converting the SAM into 1-258
aminocyclopropane-1-carboxylic acid (ACC) while the second step involves ACC 259
oxidase (ACO) which converts the ACC to ethylene (Ruduś et al. 2013) (Figure 3A). The 260
reaction catalyzed by ACS is the major rate-limiting step of ethylene biosynthesis and 261
ACO also probably becomes the rate-limiting enzyme at low oxygen and high ethylene 262
conditions (Yang and Hoffman, 1984, Kende, 1993). Rice has six putative ACS 263
(OsACS1-6) genes (Rzewuski and Sauter, 2008), but only OsACS6 expression was 264
detected in our dataset showing a similar expression pattern during submergence in 265
both genotypes. In contrast, all seven rice ACO transcripts [OsACO1-7 in Rzewuski and 266
Sauter (2008)] were detected. In both genotypes OsACO1, 2, 3 and 7 showed 267
moderate-to-high expression levels while OsACO4, 5 and 6 were expressed only at 268
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very low levels. OsACO7 was markedly induced by submergence in both genotypes, 269
showing slightly higher expression in C9285 than in T65. The expression profile of 270
genes involved in ethylene signaling were mostly similar in both C9285 and T65 plants 271
(Supplemental Figure 3A), which coincides with the similar increased levels of ethylene 272
during submergence in both genotypes (Hattori et al., 2009). 273
GA is the key hormone for submergence-induced stem elongation and 274
particularly the concentration of bioactive GA1 and GA4 increases in submerged C9285 275
plants (Hattori et al., 2009). GA biosynthesis starts from the conversion of trans-geranyl-276
geranyl diphosphate (GGDP) followed by four enzymatic steps to generate GA12 (Figure 277
3B) (Richards et al., 2001; Yamaguchi, 2008). In the later biosynthetic steps, the 278
conversion of GA12 to GA53 is catalyzed by GA13 oxidase (GA13ox) (Magome et al., 279
2013), and both GA12 and GA53 are catalyzed through two parallel pathways (the early–280
13-hydroxylation (13-OH) and non-13-OH pathways) by GA20 oxidase (GA20ox). 281
GA20ox catalyzes the conversion of GA12 and GA53 into the bioactive GA precursors 282
GA9 and GA20, respectively. Finally, GA3 oxidase (GA3ox) converts GA9 and GA20 into 283
the bioactive GA forms GA4 and GA1. The expression pattern of genes encoding the 284
enzymes before the catalytic step of GA13ox was not prominently different between 285
C9285 and T65 plants. GA20ox is the key enzyme of bioactive GA synthesis and rice 286
has four putative GA20ox genes (OsGA20ox1 to 4) (Sakamoto et al., 2004). The 287
transcripts of three OsGA20ox genes were detected in our dataset and only one of the 288
OsGA20ox genes, OsGA20ox2, was strongly expressed 1 h after submergence (>15-289
fold increase) in C9285 (Figure 3B). On the other hand, in T65, the expression level of 290
OsGA20ox2 was considerably lower (1.5 cpm in T65 vs. 72 cpm in C9285 1 h after 291
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submergence). OsGA20ox1 and OsGA20ox4 were expressed at low levels (less than 292
2.5 cpm) in both genotypes during submergence. Among the two GA3ox genes in rice, 293
only OsGA3ox2 expression was detected in both genotypes, showing a slight increase 294
after submergence. GA is inactivated by GA2ox and CYP714D1/EUI1 enzymes 295
(Sakamoto et al., 2004, Zhu et al., 2006). Among the eleven putative OsGA2ox genes in 296
rice, the expression of eight OsGA2ox was detected and the expression patterns were 297
mostly similar between the two genotypes. In our data, the expression of 298
CYP714D1/EUI1, which inactivates GA12, GA9 and GA4, could not be detected. We also 299
investigated the expression profiles of GA signaling-related genes during submergence 300
and found that SLENDER RICE-LIKE 1 (SLRL1) is expressed after submergence in 301
both genotypes, although SLENDER1 (SLR1) was not induced by submergence 302
(Supplemental Figure 3B). However, the results remain elusive because GA 303
homeostasis tightly interacts with GA metabolism and GA signaling pathways, which are 304
controlled by feed-back and feed-forward regulations and various environmental factors 305
(Sun, 2011; Hedden, 2012). 306
ABA is a negative regulator of stem elongation during submergence 307
corresponding with the decrease of ABA content in both submerged genotypes (Hattori 308
et al., 2009, Hoffmann-Benning and Kende, 1992). In higher plants, the ABA precursor 309
β-carotene is synthesized from isopentenyl pyrophosphate through the plastidial 310
methylerythritol phosphate pathway (Endo et al., 2014). β-carotene is catalyzed by 311
several enzymes and eventually converted into ABA (Figure 3C). The 9-cis-312
epoxycarotenoid dioxygenase (NCED) is a rate-limiting enzyme in ABA biosynthesis 313
and, in rice, NCED is putatively encoded by five genes (OsNCED1 to 5) (Zhu et al., 314
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2009). OsNCED1, 2 and 5 genes were detected in our dataset and the expression of 315
OsNCED2 reduced in both genotypes 1 h after submergence. Additionally, in the rice 316
genome, there are three genes that encode the ABA inactivating enzyme, ABA 8’-317
hydroxylase (ABA8ox). In our data, the OsABA8ox1 and 2 genes in both genotypes 318
showed transiently increased expression after 1 h submergence. The genes involved in 319
ABA signaling were similar expressed in both C9285 and T65 plants (Supplemental 320
Figure 3C). 321
Hoffman-Benning and Kende (1992) showed that ABA negatively regulates 322
GA-mediated stem elongation by experiments with excised stem sections of the 323
deepwater rice variety Habiganj Aman II. To test the effect of ABA on the GA activity in 324
whole plants, C9285 plants were grown from seeds for 18 days in shallow water 325
containing either GA3, ABA or a combination of both GA3 and ABA. Treatment with GA3 326
increased the total plant height and internode length compared to untreated plants 327
(Figure 3D). While treatment with ABA alone had no observable effect, treatment with 328
combined ABA and GA3 reduced the GA-induced elongation of C9285 plants. 329
Jasmonic acids (JAs) control plant growth, development and responses to 330
abiotic and biotic stresses. JAs are derived from α-linolenic acid (LA), which is released 331
from galactolipids of chloroplast membranes by fatty acid desaturase (FAD) and 332
phospholipase A1 (PLA1) including defective in anther dehiscence1 (DAD1) 333
(Wasternack and Hause, 2013) (Figure 4A). LA is converted to 3-oxo-2-(2’-pentenyl)-334
cyclopentane-1-octanoic acid (OPC-8) through the action of several enzymes including 335
lipoxygenase (LOX), allene oxide synthase (AOS), allene oxide cyclase (AOC) and 12-336
oxo-phytodienoic acid reductase3 (OPR3). After the three steps of β-oxidation, OPC-8 337
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is converted into jasmonoyl-CoA (JA-CoA) and then cleaved to (+)-7-iso-jasmonoyl [(+)-338
7-iso-JA] by thioesterase. Finally, (+)-7-iso-jasmonoyl-isoleucine (JA-IIe), which is a 339
ligand binding a co-receptor of JA receptors, is catalyzed by jasmonate resistant1 340
(JAR1) in the cytosol. Through the activity of the members of the CYP94 family, JA-IIe is 341
inactivated through hydroxylation. The putative JA-inactivating CYP94C4 gene showed 342
higher expression during submergence compared to before submergence in both 343
genotypes. In addition, endogenous JA levels decreased after 24 h of submergence in 344
both genotypes (Figure 4B). To examine the effect of JA on the submergence response, 345
we submerged C9285 plants in water containing 50 µM methyl-jasmonate and 346
measured the total internode length after three days of treatment (Figure 4C). 347
Surprisingly, treatment with JA remarkably inhibited the submergence-induced internode 348
elongation. 349
350
Deepwater treatment has genotype-specific effects on trehalose metabolism and 351
fermentation-related pathways 352
353
We further investigated the expression of genes in other relevant pathways to 354
understand the metabolic adaptation of deepwater rice under submergence. 355
Comparative analysis of metabolic pathways using the MAPMAN software showed that 356
genes related to the metabolism of trehalose (Supplemental Figure 4A) and 357
fermentation (Supplemental Figure 4B) were induced in response to 1 h submergence 358
in C9285 plants. Expression of genes in the NO3-generating pathway (Supplemental 359
Figure 4C) was also up-regulated after submergence, but their absolute expression was 360
at very low levels. 361
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362
Trehalose is a disaccharide that functions in carbon metabolism and tolerance 363
to biotic and abiotic stresses (Lunn et al., 2014). In plants, trehalose is synthesized in a 364
two-step process from UDP-glucose (UDPG) and glucose-6-phosphate (Glu6P) by the 365
subsequent actions of trehalose-6-phosphate synthases (TPS) and trehalose-6-366
phosphate phosphatases (TPP) and the degradation of trehalose is catalyzed by 367
trehalase (TRE) (Figure 5A, Ponnu et al., 2011). In our dataset, we detected the 368
expression of trehalose metabolism-related genes including 13 TPS (out of 14), 7 TPP 369
(out of 13) and one TRE (Ge et al., 2008). Some TPS genes clearly responded to 370
submergence in C9285 plants. Notably, three TPS genes (OsTPS12, OsTPS13, 371
OsTPS14) were strongly induced in response to submergence in C9285 plants but not 372
in T65 plants (Figure 5B). OsTPP1 and OsTPP11 showed elevated expression in 373
response to submergence in C9285 plants while OsTPP2 expression was induced at a 374
relatively low level in T65 after submergence (Figure 5C). In the case of TRE, the 375
expression pattern was similar in both genotypes (Figure 5D). 376
Under anaerobic conditions, oxygen is limited for aerobic respiration and plant 377
cells implement anaerobic respiration (glycolysis and fermentation) for energy 378
production instead (Perata et al., 1998; Fukao and Bailey-Serres, 2004, Bailey-Serres 379
and Vosencnek, 2008; Miro and Ismail, 2013). The glycolysis pathway generates ATP 380
and the following fermentation steps produce NAD+ for maintenance of glycolysis and 381
some metabolites. Fermentation converts the glycolysis-derived pyruvate into other 382
metabolites such as alanine, lactate, ethanol and acetate (Figure 6A). Alanine is 383
synthesized from pyruvate and glutamate by the alanine aminotransferase (AlaAT) while 384
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19
lactate is formed by the reduction of pyruvate via lactate dehydrogenase (LDH). 385
Pyruvate decarboxylase (PDC) converts pyruvate to acetaldehyde. To detoxify 386
acetaldehyde, alcohol dehydrogenase (ADH) or acetaldehyde dehydrogenase (ALDH) 387
subsequently catalyzes the conversion of acetaldehyde to ethanol or acetate, 388
respectively. Interestingly, we found that the two LDH genes (LDH-A and LDH-B) were 389
strongly and specifically induced 1 h after submergence in C9285 but not in T65 plants 390
(Figure 6B). Among other fermentation-related genes, the OsAlaAT1, OsPDC1, 2 and 3, 391
Os05g0469800, OsADH1 and 2, and OsALDH2a appeared to increase after 392
submergence in both genotypes whereas the genes in ALDH1 family seemed to show 393
variable expression pattern during submergence. 394
395
Submergence induces differential expression profiles of genes related to cell wall 396
formation between C9285 and T65 plants 397
398
Under the non-submerged condition, genes related with cell wall formation and 399
secondary metabolic pathways showed higher expression in C9285 plants compared to 400
T65 plants (Supplemental Figure 5A to 5D). The plant cell wall provides mechanical 401
strength, regulates growth, serves as a barrier to diffusion, and protects the plant 402
against pathogens. The cell wall-related transcripts with higher expression in C9285 403
plants encoded cell wall modification proteins α- and β-expansins (EXPAs and EXPBs), 404
xyloglucan endotransglycosylases/hydrolases (XTHs), pectin esterases (PMEs) and 405
structural cell wall proteins [fasciclin-like arabinogalactans (FLAs) and extensins] 406
(Figure 7A). In T65 plants, almost all genes responded to submergence and the 407
expression level finally reached that of C9285 within 24 h submergence. In C9285 408
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20
plants, several genes were strongly induced by submergence, especially the genes 409
EXPB6, EXPB7, OsXTH23, OsXTH1 and two PMEs (Os01g0880300 and 410
Os01g0312500), three FLAs (FLA7, FLA6 and FLA2) and two extensins 411
(Os02g0138000 and Os01g0594300) remarkably responded to submergence in C9285 412
plants. 413
Under non-submerged conditions, genes involved in flavonoid, anthocyanin, 414
and phenylpropanoid metabolism, as well as in the biosynthesis of lignin and simple 415
phenols (e.g., laccases involved in lignin polymerization), were expressed higher in 416
C9285 compared to T65 (Supplemental Figure 5C). Lignin is a complex polymer of 417
monolignols and strengthens the cell wall as a component of secondary cell walls. Thus, 418
cell wall lignification probably functions in the suppression of rapid growth in deepwater 419
rice resulting in a slow rate of elongation of its stems in non-submerged conditions 420
(Sauter and Kende 1992). We investigated the transcriptional responses of lignin 421
biosynthesis-related genes to submergence and focused on genes encoding 422
coniferyl/sinapyl alcohol dehydrogenase (CAD/SAD), which catalyzes the final step of 423
monolignol biosynthesis (Supplemental Figure 6A). In C9285 plants, among the 11 424
CAD/SAD genes (out of a total of 12 genes in the genome), OsCAD1, OsCAD2, 425
OsCAD8B and OsCAD8C were highly expressed in non-submerged conditions and, 426
except for OsCAD1, showed decreased expression in response to submergence 427
(Figure 7B). The OsCAD1 showed a similar expression level in both genotypes while 428
the other CAD genes in T65 maintained lower expression levels during submergence. 429
To determine whether the decrease in expression of CAD genes affects lignin 430
biosynthesis in elongating internodes of C9285 plants, we measured the lignin content 431
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of the C9285 stem including (1) nodes from different positions, (2) non-elongated 432
internodes (an internode that already stopped elongating) and (3) newly-elongated 433
internode (newly elongating internode during submergence) (Figure 7C). Under non-434
submerged condition, the basal node, non-elongated internode, and the 2nd and 3rd 435
nodes showed similar lignin content (Figure 7D). The total lignin content in the basal 436
and 2nd nodes did not change after 2 days of submergence (Figure 7D, 7E). On the 437
other hand, the 3rd node on the internode newly-elongated after 2 days of submergence 438
exhibited a lower lignin content (Figure 7E). The total lignin content in the non-439
elongating internode was not affected by 2 days of submergence while the content of 440
the newly-elongated internodes was lower than that of the non-elongated internode. 441
These results suggest that suppression of lignin biosynthesis through the reduction of 442
CAD transcripts contributes to the elongation of internodes in C9285 plants. In 443
agreement with this, the lignin content in the basal nodes of T65 plants did not change 444
during submergence (Supplemental Figure 6B). 445
446
Expression of ERF transcription factor genes in response to submergence 447
448
The MAPMAN overrepresentation analysis revealed that transcription factor (TF) genes 449
from the AP2/EREBP family were significantly enriched among genes induced by 450
submergence in both genotypes (Supplemental Table 4A and 4B). To investigate the 451
response of all TF genes to submergence, the genes in our dataset were categorized 452
according to the Plant Transcription Factor Database v3.0 (Oryza sativa ssp. Japonica) 453
(plantTFDB; http://planttfdb.cbi.pku.edu.cn/; Jin et al., 2014) (Supplemental Data Set 8, 454
Supplemental Figure 7 and Supplemental Results). Interestingly, those clusters 455
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22
contained a total of 10 ethylene response factor (ERF) genes (Supplemental Figure 7). 456
The ERFs belong to the AP2/EREBP superfamily which is a plant-specific transcription 457
factor family with three sub-families, (1) AP2 family proteins containing two repeated 458
AP2 DNA-binding domains, (2) ERF family proteins containing a single AP2 domain and 459
(3) RAV family proteins containing a B3 DNA-binding domain and a single AP2 domain 460
(Riechmann and Meyerowitz, 1998; Sakuma et al., 2002; Nakano et al., 2006). Nakano 461
et al. (2006) divided the rice ERF family (total of 139 genes) into 15 subfamilies 462
including 28 subgroups. In our dataset, we categorized the ERF genes into these 463
subgroups. Among all TFs in our dataset, 115 were found to be ERF genes including 41, 464
10, and 64 genes with increased, decreased and unchanged expression during 465
submergence, respectively (Supplemental Table 5). The ERF genes from subgroups IIa, 466
IIIc, VIIa, VIIb, IXa, Xa, Xb, Xc and XI predominately showed an increased expression in 467
response to submergence in C9285 plants while those of subgroups IIIe and Va showed 468
decreased expression under submergence treatment. Supplemental Figure 8 shows 469
expression profiles of the submergence-induced ERF genes. The SUB1 locus encodes 470
three ERF transcription factor genes (SUB1A, 1B and 1C) (Xu et al., 2006); however, 471
the genome of C9285 contains only Sub1B and Sub1C but does not have Sub1A 472
(Hattori et al., 2009). In C9285 plants, SUB1B (OsERF#063) and SUB1C (OsERF#073) 473
increased 3.2-fold and 2.7-fold 1 h after submergence, respectively (Supplemental 474
Figure 8A). The expression of SK1 and SK2 genes, which are positive regulators of 475
internode elongation in C9285 plants and absent in T65 plants, was also remarkably 476
increased 5.3-fold and 3.2-fold by submergence, respectively (Supplemental Figure 8B). 477
478
479
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23
GCC-box like promoter elements are enriched in the promoters of genes 480
specifically expressed in C9285 plants 481
482
483
Using k-means clustering, we isolated 189 genes which are specifically expressed in 484
C9285 plants (Supplemental Data Set 9). Their putative promoter regions (1 kb 485
upstream from the transcriptional start site) were constructed by aligning reads from 486
genomic DNA of C9285 plants to the Oryza sativa ssp. Japonica cv. Nipponbare 487
reference genome. The constructed promoter sequences were then analyzed for 488
enriched DNA sequence motifs using Multiple EM for Motif Elicitation (MEME) suite. We 489
found two GCC-box like elements (GCGGCGGCGG and CGCCGCCGCC) enriched in 490
sequence among the analyzed promoter sequences (Supplemental Figure 9). The 491
consensus DNA-binding motif (GCCGCC) is known to be recognized by the ERF 492
proteins (Hao et al. 1998; Fujimoto et al., 2000). 493
494
Identification and analysis of differentially expressed genes unique to 495
C9285. 496
497
Although about 85% of C9285 RNA-Seq reads could be mapped to the Nipponbare 498
reference genome (Supplemental Table 1), there is a possibility that C9285 has 499
additional genes missing in the reference genome, such as SK1 and SK2. Hence, we 500
performed a targeted de novo assembly of transcripts to detect C9285-specific 501
transcripts (Supplemental Figure 10 and Supplemental Methods). We used 47,978,704 502
paired-end reads from genomic DNA of C9285 (ca. 20x coverage) to assemble C9285-503
specific genomic regions and quantified transcripts detected in those regions using 504
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24
RNA-Seq reads. We then restricted our analysis to those transcripts which are either 505
expressed at high levels, are strongly induced by submergence, or have an interesting 506
annotation. In total, 86 transcribed loci on 33 genomic contigs were found to be either 507
putatively unique to C9285 or sufficiently different from the Nipponbare reference so that 508
mapping with standard parameter failed to produce alignments (Supplemental Data 509
Sets 10, 12 to 14). 510
Among those 86 loci, two encoded the full-length SK1 and SK2 transcripts. 511
The genomic contigs that contained the SK1 (contig_21; 5,776 bp) and SK2 (contig_8; 512
12,025 bp) loci aligned almost perfectly with parts of the BAC clone that was used for 513
map-based cloning of SK1 and SK2 (Hattori et al., 2009). When we quantified the 514
expression of SK1 and SK2 genes from those contigs, we found the typical early 515
increase of transcriptional activity 1 h after submergence with subsequent decline 516
(Supplemental Figure 8B). This shows that our targeted assembly strategy was able to 517
correctly identify unique C9285 transcripts, including their genomic sequence and their 518
expression patterns. We found 11 novel transcripts that had at least two-fold higher 519
expression level after 1 h submergence (Figure 8). Except for SK1 and SK2, most of 520
those transcripts did not encode well-characterized proteins. Instead, a sequence 521
comparison using blastp reported at least six pathogen- or disease-related proteins. The 522
remaining three proteins were annotated as domain of unknown function, 523
retrotransposon-related and SAM-dependent methyl transferase. 524
525
526
527
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25
528
529
DISCUSSION 530
The overall goal of this study was to understand the transcriptional responses 531
associated with the ‘escape strategy’ of the deepwater rice C9285 during submergence. 532
Cataloguing the whole transcriptome through an RNA-seq approach revealed 533
differences in gene expression between deepwater rice (C9285) and non-deepwater 534
rice (T65) plants, as well as unique and common responses to submergence in the two 535
genotypes. The results of our comprehensive transcriptome analysis contribute to the 536
finding of key genes regulating the metabolic pathways during submergence in rice. 537
538
Transcripts associated with ethylene, GA, and ABA metabolism are differentially 539
expressed in response to submergence 540
Previous studies have demonstrated that the hormones ethylene, gibberellin 541
(GA), and abscisic acid (ABA) modulate the internode elongation response of 542
submerged deepwater rice (Kende et al., 1998). Among the ethylene biosynthesis 543
genes, it is reported that OsACS1, OsACS5, and OsACO1 were increased by 544
submergence in deepwater rice (Mekhedow and Kende 1996; Zarembinski and 545
Theologis 1997; van Der Straeten et al. 2001). On the other hand, in our data, OsACO7 546
transcript and protein accumulated during submergence in both genotypes (Figure 3A, 547
Supplemental Figure 11A). Ethylene accumulation in submerged deepwater rice is 548
attributed to the decrease in ethylene diffusion and enhancement of ethylene 549
biosynthesis (Métraux and Kende (1983). Our previous study showed that ethylene 550
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26
accumulation is a common occurrence in both C9285 and T65 plants (Hattori et al., 551
2009). Our transcript analysis supports that OsACO7 is involved in ethylene 552
accumulation in both genotypes during submergence. OsACO7 has not been reported 553
to participate in ethylene biosynthesis during submergence, although most previous 554
studies used non-deepwater rice varieties. 555
Under submergence condition, the accumulated ethylene enhances GA 556
accumulation for the promotion of internode elongation in deepwater rice (Métraux and 557
Kende, 1983, 1984; Raskin and Kende, 1984b; Kende et al., 1998). Interestingly, unlike 558
ethylene biosynthesis, the activation of GA biosynthesis occurs only in C9285 plants 559
(Hattori et al. 2009). In our data, OsGA20ox2 (also known as SD1) expression levels 560
were strongly and specifically induced by submergence in C9285, but not in T65 (Figure 561
3B). GA20ox2 is a key locus for GA production and its increased expression is thus 562
most likely responsible for the higher GA1 and GA4 accumulation in submerged C9285 563
plants (Supplemental Figure 12F, Hattori et al., 2009, Ayano et al., 2014). In the case of 564
the submergence-tolerant rice with SUB1A, SUB1A suppresses GA signaling through 565
accumulation of GA signaling repressors, SLR1 and SLRL1, leading to restricted 566
elongation of stems and leaves under submergence (Fukao and Bailey-Serres, 2008; 567
Colebrook et al., 2014). Thus, the absence of SUB1A in the deepwater rice C9285 may 568
explain the accumulation of bioactive GA levels promoting the elongation of stems and 569
leaves during submergence. It has been reported that the GA-induced genes, Oryza 570
sativa Growth Regulating Factor1 (OsGRF1) and a GA stimulated transcript (GAST)-like 571
gene, OsGSR1, enhance the stem elongation in rice (van der Knaap et al., 2000; Ben-572
Nissan et al., 2004; Choi et al, 2004; Wang et al., 2009). Interestingly, two GAST-like 573
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27
genes (Os05g0376800 and OsGSR1) were expressed higher in C9285 plants during 574
submergence, although OsGRF1 was not induced during submergence in our dataset 575
(Supplemental Figure 11B and 11C), suggesting that the GAST-like genes may be 576
involved in GA-induced stem elongation during submergence in C9285 plants. 577
The content of ABA, which has the antagonistic effect to GA on internode 578
elongation, decreased under submergence and ethylene treatments (Hoffman-Benning 579
and Kende, 1992; Azuma et al.,1995; Benschop et al., 2006; Yang and Choi, 2006; 580
Weiss and Ori, 2007; Saika et al., 2007; Fukao and Bailey-Serres, 2008a; Hattori et al., 581
2009; Chen et al., 2010). The decrease in ABA content is a common response to 582
submergence in both T65 and C9285 plants (Hattori et al. 2009). Our data revealed that 583
transcript levels of OsNCED2, encoding one of the rate-limiting enzymes in ABA 584
biosynthesis decreased, and OsABA8ox1 and OsABA8ox2 encoding ABA inactivation 585
enzymes were up-regulated in both genotypes during submergence (Figure 3C), 586
indicating that the decrease in ABA content may be explained by the changes in 587
expression level of genes related to ABA metabolism in both genotypes. 588
589
Jasmonic acid is a novel regulatory factor associated with stem elongation in 590
deepwater rice 591
Kende et al. (1998) reported that ethylene, ABA and GA are key regulators of 592
internode elongation in deepwater rice. In this study, we demonstrated that 593
submergence regulated the endogenous jasmonic acid (JA) content in node samples of 594
rice and JA inhibited the submergence-induced internode elongation in C9285 plants 595
(Figure 4). CYP94C2b encodes a cytochrome P450 enzyme and was involved in the 596
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28
inactivation of JA-Ile (Kurotani et al., 2015). Our data showed that CYP94C4, which is a 597
major expressed CYP94C gene, showed increased expression levels during 598
submergence in both genotypes. Thus, the increase in CYP94C4 might regulate the 599
decrease in endogenous JA content. The decrease in JA is a common response to 600
submergence in both genotypes, like the changes in ethylene and ABA contents during 601
submergence. The non-deepwater rice T65 at 6LS has no ability to elongate its 602
internodes even in the case of GA treatment (Nagai et al., 2014), suggesting that the 603
changes in JA contents in T65 plants does not affect the stem elongation. 604
Studies on cross-talk between JA and GA signaling pathways have shown that 605
GA antagonistically functions in JA signaling pathways involved in plant growth and 606
development processes in Arabidopsis (Hou et al., 2013, Wasternack and Hause, 607
2013). In addition, Yang et al. (2012) showed that JA-mediated growth inhibition in rice 608
was caused by changes in the levels of DELLA repressors and interference with GA-609
signaling. Our data suggest that GA-mediated internode elongation in deepwater rice 610
requires suppression of JA function through the reduction of JA content in 611
submergence. 612
613
614
C9285 and T65 plants differentially express trehalose and fermentation 615
metabolism-related genes 616
Trehalose, which accumulates in response to various stresses, acts as a 617
carbon source and an osmoprotectant by stabilizing the proteins and membranes 618
against the stresses (Krasensky and Jonak, 2012). On the other hand, trehalose-6-619
phosphate (Tre6P), a precursor of trehalose, functions as a signaling metabolite which 620
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29
coordinates carbon assimilation, starch synthesis, nitrogen metabolism, growth and 621
development (Schluepmann et al., 2003; Martins et al., 2013; Lunn et al., 2014; Yadav 622
et al., 2014; Figueroa et al., 2016; Figueroa and Lunn, 2016). The change in 623
Tre6P/sucrose ratio is an important homeostatic mechanism of plants under stress 624
conditions and thus Tre6P also acts as a signal for sucrose status through negative 625
feedback regulation of sucrose levels (Yadav et al., 2014; Figueroa and Lunn, 2016). In 626
rice, overexpression of OsTPS1 or OsTPP1 enhanced the tolerance to abiotic stresses, 627
leading to the expression of stress-related genes (Ge et al., 2008; Li et al., 2011). 628
OsTPP7 (OsTPP11 in this paper) also enhances the anaerobic germination tolerance in 629
young rice by regulating the trehalose content and Tre6P/sucrose homeostasis in sugar 630
signaling, but not the Tre6P content (Kretzschmar et al., 2015). In our data, although 631
several OsTPS genes including OsTPS1, OsTPP1 and OsTPP11 were expressed by 632
submergence in both genotypes, the expression of OsTPS12, 13, and 14 was 633
dramatically induced by submergence in C9285 but maintained at a lower level in T65 634
(Figure 5B). This result implies that trehalose metabolism during submergence is 635
differentially regulated between C9285 and T65 and that trehalose and trehalose-6-636
phosphate (Tre6P) may be accumulating more in submerged C9285 plants, contributing 637
to the ability of deepwater rice to withstand and adapt to submergence stress. In 638
submerged SUB1A-1 containing M202(SUB1) rice seedlings and anoxic coleoptiles, the 639
trehalose biosynthesis pathway is activated (Jung et al., 2010), suggesting that such a 640
pathway is also being utilized by the deepwater rice as part of metabolic adaptation to 641
submergence. 642
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30
Under low oxygen condition, glycolysis is predominantly channeled to 643
fermentation pathways (instead of aerobic respiration) which is necessary for cell 644
survival to produce energy and recycle carbon for other pathways (Gibbs and 645
Greenway, 2003; Voesenek et al., 2006). Our data exhibited the increased expression 646
of fermentation-related genes, pyruvate decarboxylases (PDCs), alcohol 647
dehydrogenases a and 2 (ADH1 and ADH2) and acetaldehyde dehydrogenase2a 648
(ALDH2a), during submergence in both genotypes (Figure 6B). A functional SUB1 locus 649
regulates the gene expression and enzyme activities of PDC and ADH during 650
submergence (Fukao et al., 2006). Thus, a SUB1A-1 containing rice, Flood Resistant 651
13A (FR13A), accumulates less aldehydes because high expression of ADH enhances 652
the detoxification of acetaldehyde into the neutral and diffusible ethanol (Singh et al., 653
2001, Xu et al., 2006). Submergence also induces the expression of ALDH2a, but not 654
ALDH1, in coleoptiles of rice (Nakazono et al. 2000). Our results imply that the 655
fermentation pathway is active in both genotypes and that the enzymes ADH and 656
ALDH2a is likely involved in removing toxic alcohol and acetaldehyde in response to low 657
oxygen during submergence (Figure 6A). 658
The increased expression of alanine aminotransferase1 gene (OsAlaAT1) 659
(Figure 6B) further supports that the active fermentation pathway in C9285 and T65 also 660
generates alanine. These results are consistent with the increased activities of AlaAT, 661
PDC and ADH in the flooded coleoptile of rice (Oryza sativa L. cv. Nipponbare) (Kato-662
Noguchi, 2006); however, in their study, the activity of lactate dehydrogenase (LDH), 663
and lactate content were similar both in the presence and absence of oxygen. In our 664
dataset, the transcripts of two LDH genes in C9285 plants were strongly upregulated 665
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31
after submergence, compared to T65 plants (Figure 6B). Formation of lactate leads to a 666
decrease in cytosolic pH and the initial acidification of the cytoplasm helps to achieve 667
optimum activity of PDC, which in turn promotes the switch from lactate to ethanol 668
fermentation (Kennedy et al., 1992; Roberts et al. 1994; Magneschi and Perata, 2009). 669
Hence, it is possible that the abundance of LDH transcripts results in higher 670
accumulation of lactate in the cytoplasm and a stronger lactate-dependent reduction of 671
cytosolic pH favoring ethanol fermentation more in C9285 than in T65 plants. Recently, 672
Lee et al. (2015) reported that lactate binds to NDRG3, an oxygen-regulated protein, 673
and activates Raf-ERK signaling for promoting cell growth and angiogenesis during 674
hypoxia in human cells, suggesting that lactate in plant cells might function as a 675
signaling molecule in a similar signaling pathway in response to hypoxia. 676
677
Cell wall synthesis and modification genes are differentially expressed in C9285 678
plants in response to submergence 679
Genes with a differential response to submergence between C9285 and T65 680
plants were enriched in the cell wall-related category (Supplemental Figure 2C). 681
Additionally, genes encoding cell wall-related proteins such as expansins (EXPs), 682
xyloglucan endotransglycosylases/hydrolases (XTHs), pectin methylesterases (PMEs), 683
and structural cell wall proteins [fasciclin-like arabinogalactans (FLAs) and extensins] 684
were categorized as submergence-induced genes in both genotypes (Supplemental 685
Table 4A and 4B) and showed higher expression in C9285 plants under non-submerged 686
condition (Figure 7A). Elongating cells require relaxation of cell walls involving cell wall 687
loosening factors such as expansins. Expansin activity increases under acidic condition, 688
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32
which is controlled by plasma membrane H+-ATPase activity via auxin-induced SMALL 689
AUXIN UP-RNA (SAUR) proteins (Perrot-Rechenmann 2010, Spartz et al., 2014). In 690
deepwater rice, a positive correlation was observed between the expression of EXPs 691
and acid-induced cell wall extensibility, and they may be functioning in internode 692
elongation (Cho and Kende, 1997a; Cho and Kende, 1997b; Lee and Kende 2001). The 693
EXPs together with XTHs control fiber orientation and viscoelastic properties of the 694
matrix facilitating cell wall expansions (Cosgrove, 2000, Van Sandt et al., 2007). XTH 695
activity possibly enhances the EXP activity during the shade avoidance elongation 696
response in S. longipes (Sasidharan et al., 2008). In rice, XTHs could function in the cell 697
wall formation of the vascular bundles in elongating stems (Hara et al., 2013). 698
PMEs catalyze the demethylesterification of pectin, a galacturonic acid-rich cell 699
wall polymer resulting in the formation of a gel-like structure of polymers and thereby 700
increase wall porosity and extension of cells (Jolie et al., 2010). Jeong et al. (2015) 701
investigated that high PME activity was detected in germinating shoots that actively 702
undergo cell elongation. The cell wall is also regulated by structural cell wall proteins, 703
for instance, the arabinogalactan proteins (AGPs) which are involved in elongation and 704
growth of Arabidopsis and cucumber (van Hengel and Roberts, 2002; Park et al., 2003). 705
We found that that the expression of several genes related to cell wall loosening were 706
induced. These genes might contribute to cell wall reconstruction and increased cell 707
wall extensibility, leading to further enhancement of rapid internode elongation of C9285 708
plants during submergence. 709
Accumulation of lignin is part of the cell wall modifications that lead to an 710
increase in mechanical strength but also inhibits cell elongation. In C9285 plants, the 711
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33
expression of several CAD genes, encoding key enzymes that catalyze the final step in 712
monolignol synthesis, decreased during submergence (Figure 7B), leading to a reduced 713
lignin content in newly-elongated internode during submergence. (Figure 7E). 714
Peroxidase genes showed differential expression pattern between both 715
genotypes under submergence (Supplemental Figure 2C and supplemental results) and 716
were classified as submergence-induced genes (Supplemental Tables 4A and 4B). 717
Interestingly, the expression levels of the peroxidase genes were higher in C9285 plants 718
than in T65 plants during early submergence condition (Supplemental Figure 6C). 719
Peroxidases are involved in lignification, stress defense, and regulation of reactive 720
oxygen species production (Shigeto and Tsutsumi, 2016). In addition, hydroxyl radicals 721
(・OH) produced by peroxidases may also function in cell wall loosening and cell 722
elongation as in maize roots (Liszkay et al., 2004). Thus, submergence-responsive 723
peroxidases probably function in cell wall loosening and lignification of elongating 724
internodes in C9285 plants. 725
726
Ethylene response factor genes are differentially regulated in submerged C9285 727
and T65 plants 728
Ethylene response factors (ERFs) are major downstream components of the 729
ethylene signaling pathway. In our analysis, among the 115 detected ERF family 730
transcripts, 39 genes in Ib, IIa, IIIc, VII, VIIIa, IXa, X and XI subgroups were up-731
regulated and 10 genes in IIIe and Va subroups were down-regulated by submergence 732
in C9285 plants, respectively (Supplemental Table 5), indicating that ethylene signaling 733
is an important regulatory pathway for the response of deepwater rice to submergence. 734
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34
Interestingly, among all 15 members of the Group VII ERF family, 12 genes 735
including SUB1B (OsERF#063) and SUB1C (OsERF#073) were induced by 736
submergence in C9285 plants (Supplemental Table 5; Supplemental Figure 8A). 737
Members of Group VII ERF family act as oxygen sensors under hypoxic conditions by 738
the N-end rule pathway for protein degradation in Arabidopsis (Gibbs et al., 2011, 739
Licausi et al., 2011; Gasch et al., 2016) and function in multiple stress tolerances such 740
as drought, cold, pathogen attack, salinity, osmotic stress, and submergence in various 741
plants (Licausi et al., 2010; Mizoi et al., 2002; Gibbs et al., 2015, Papdi et al., 2015). We 742
found the other 3 genes (OsERF#70, #71, #72) encoding a CMVII-4 motif, which is 743
predicted to be a phosphorylation site of mitogen activated protein kinases (MPKs) 744
(Nakano et al., 2006), showed non-responsive expression to submergence in C9285 745
plants (Supplemental Figure 13). MPKs phosphorylate a large of transcription factors 746
including ERFs (Popescu et al., 2009) and the MPK-induced phosphorylations in rice 747
ERFs enhance their transcriptional activities and environmental stress tolerances 748
(Cheong et al., 2003; Schmidt et al., 2013). Recently, it was reported that OsMPK3 749
phosphorylated SUB1A-1 to control shoot elongation in a SUB1A-1-dependent manner, 750
although the phosphorylation site was not located in the CMVII-4 motif (Singh and 751
Sinha, 2016). In C9285 plants, all members of Group VII ERFs that encode proteins 752
without the phosphorylation sites were induced by submergence and the submergence-753
induced expression level of some Group VII ERFs (OsERF#59, 61, 63, 64, 66 and 67) 754
was higher during submergence compared to T65 plants (Supplemental Figure 13). 755
These results suggest that phosphorylation-independent Group VII ERFs may be 756
important for the submergence-induced stress response in deepwater rice, although 757
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35
there is still the possibility that submergence induces phosphorylation of the ERFs by 758
MAP kinases. 759
Other submergence-induced ERFs in subgroups IIa and VIIIa encode proteins 760
that contain an ERF-associated amphiphilic repression (EAR) motif (DLNxxP), which 761
acts as a transcriptional repressor domain (Fujimoto et al., 2000; Ohta et al., 2001). As 762
EAR-containing transcription factors regulate various stress responses (Kazan, 2006; 763
Dong and Liu, 2010; Licausi et al., 2013), the submergence-induced ERFs might be 764
involved in negatively regulating the expression of dispensable genes for submergence 765
response. 766
In our data, Group IIIc, IXa and X ERFs also showed up-regulated expression 767
in response to submergence (Supplemental Table 5). In Arabidopsis, the group IIIc, IXa 768
and X ERFs function in tolerance to environmental stresses such as freezing, salt and 769
dehydration (e.g. cold-binding factor/dehydration responsive element binding1 770
[CBF/DREB1] protein) (Dubouzet et al., 2003), the ethylene-jasmonic acid signaling 771
pathway (Lorenzo et al., 2003, Champion et al., 2009) and the response to ABA and 772
various stresses (Pandey et al., 2005; Zhu et al., 2010), respectively. In the case of the 773
Group XI ERFs, this family exists in rice but not in Arabidopsis, indicating that these 774
genes have rice-specific functions. 775
A Group IIIe ERF, TINY, functions in the reduction of cell expansion and 776
differentiation leading to a dwarf phenotype in Arabidopsis (Wilson et al., 1996). In 777
C9285 plants, two Group IIIe ERF family genes were down-regulated by submergence, 778
suggesting that the Group IIIe ERFs possibly affects cell expansion during 779
submergence. Arabidopsis ERF11 in group VIIIa represses ethylene biosynthesis genes 780
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36
but promotes cell elongation by promoting GA accumulation and inhibition of DELLA 781
function (Li et al., 2011; Zhou et al., 2016). In rice, OsEATB (OsERF#102) in group Xb 782
and OsERF3 (OsERF#075) in group VIIIa negatively regulates internode elongation (Qi 783
et al., 2011; Zhang et al., 2013), respectively. In C9285 plants, OsEATB was not 784
expressed and OsERF3 was not differentially expressed during submergence 785
(Supplemental Figure 11D), suggesting that the two negative regulators do not 786
participate in GA-mediated internode elongation during submergence in C9285 plants. 787
The SUB1A up-regulates the transcriptional expression level of 12 ERF family 788
genes (Jung et al., 2010). Although the SUB1A gene is not present in C9285 genome 789
(Hattori et al., 2009), the six SUB1A-dependent expressed genes (i.e., OsERF#025, 790
#066, #067, #068, #076 and #077) were also induced by submergence in C9285 plants 791
(Supplemental Figure 8A). All SUB1A downstream ERF genes belong to IIIc, VIIa and 792
VIIIa subfamilies. This indicates that these genes are also regulated by other factors in 793
C9285 plants and may also indicate that their expression is not directly associated with 794
internode elongation in deepwater rice. 795
The ERF transcription factors bind to the promoter regions of their target genes 796
such as pathogen-related (PR) genes through recognition of a GCC box cis-regulatory 797
sequence (GCCGCC; core motif) (Ohme-Takagi and Shinshi, 1995; Hao et al., 1998, 798
Solano et al., 1998). Our in-silico analysis showed that the two GCC-box like motifs 799
(G/CCGGCGGCGG) and (CGCCGCCGCC) were enriched in the promoter region of 800
genes with higher expression in C9285 plants (Supplemental Figure 9), suggesting that 801
these genes with GCC-box like motifs are preferentially regulated by ERFs. Some 802
submergence-induced ERF genes showed higher expression in C9285 than those of 803
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37
T65 plants before and after submergence (Supplemental Figure 8A). This result 804
suggests that the ERF genes in C9285 are associated with the constitutively higher 805
expression of their putative downstream target genes. Recently, Gasch et al. (2016) 806
identified a novel hypoxia-responsive promoter element (HRPE) which is a binding site 807
of ERF VIIs, RELATED TO AP2 (RAP) 2.2 and RAP2.12, the key regulators of N-end 808
rule pathway in Arabidopsis. However, we did not identify the HRPE motif in our 809
promoter analysis of C9285-enriched genes. The O2 levels in underwater nodes could 810
be much higher than expected for two reasons: (i) diffusion from the water layer into the 811
node, and (ii) underwater photosynthesis. Under submergence with light illumination, O2 812
concentration of deepwater rice initially dropped but recovered within 90 min by its 813
underwater photosynthesis (Stünzi and Kende, 1989). Thus, our data may not be 814
suitable to study hypoxia, since we collected all samples under light condition. 815
816
A model for the transcriptional response of deepwater rice to submergence 817
We propose a model for submergence responses during the “escape strategy” in 818
the deepwater rice C9285 (Supplemental Figure 14). Submergence subjects the plant 819
cells to multiple stresses such as limitation of gas diffusion, lower light intensity, high risk 820
of pathogen infection and decreased oxygen uptake. To avoid critical damage from 821
submergence, C9285 plants have evolved to rapidly elongate their internodes and 822
leaves. We revealed that changes in contents of the plant hormones, ethylene, ABA, GA 823
and JA during submergence were transcriptionally regulated. Ethylene signaling leads 824
to biotic and abiotic stress tolerances by changing the expression of many genes and 825
plant hormone levels (Müller and Munné-Bosch, 2015) and our data exhibited largely 826
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38
changes in the putative downstream components of ethylene signaling during 827
submergence. We also proposed that JA is a novel regulator for submergence-induced 828
internode elongation in C9285 plants. In deepwater rice, GA has an important role in 829
elongation response because GA treatment induces the expression of cell wall-related 830
genes such as expansins and changes the activity of CAD (Sauter and Kende 1992, 831
Cho and Kende 1997c). We found that C9285-specific accumulation of active GAs was 832
probably controlled by the expression of GA20ox2 during submergence (Figure 3B) and 833
the cell wall-related genes showed higher expression in C9285 plants (Figure 7A). 834
Furthermore, the reduced lignin content in C9285 plants may also facilitate the 835
elongation of internodes under submerged condition. Overall modifications in cell wall 836
metabolism may also be contributing to the rapid internode elongation of deepwater 837
rice. Among the transcription factor genes, the ERF family genes were especially 838
expressed at high levels during submergence in C9285 plants. Interestingly, genes 839
specifically expressed in C9285 plants contain the GCC-box like motifs which are 840
recognized by ERFs. This indicates that ethylene signaling and the transcriptional 841
response pathway via ERFs could be a key factor for submergence response in C9285 842
plants. In fact, the rice ETHYLENE INSENSITIVE3-like 1 (OsEIL1), which is the master 843
regulator of ethylene signaling, binds to the promoter region of ethylene/submergence-844
induced ERF transcription factors, SNORKEL1 and SNORKEL2 (SK1/2), that positively, 845
but not exclusively, regulate internode elongation in C9285 plants (Hattori et al., 2009). 846
Since we could not find any C9285-specific novel submergence-induced TFs in the 847
C9285 genome by our de-novo assembly analysis and the presence of SK1/2 alone 848
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39
does not lead to a full stem elongation response, additional TFs in coordination with 849
SK1/2 are most likely involved. 850
In Rumex palustris, genes associated with photomorphogenesis and shade 851
avoidance seem to regulate underwater elongation response (van Veen et al. 2013). In 852
our data, the expression pattern of light signaling regulated genes in C9285 plants did 853
not show any obvious genotype or submergence-specific pattern (Supplemental Figure 854
15). The genes involved in fermentation and trehalose metabolic pathways responded 855
to submergence in both C9285 and T65 plants, and we found that TPSs and LDHs were 856
preferentially expressed during submergence in C9285 plants (Figure 5 and 6), 857
suggesting that these metabolic activities increase more strongly in C9285 plants during 858
submergence, compared to normal rice such as T65 plants, resulting in adaptation to 859
long-term submergence. 860
Our experiments showed that many pathogenesis related proteins (PR-861
proteins) were preferentially expressed in each rice variety (Supplemental Table 3) and 862
several genes encoding disease resistance proteins were identified as C9285-unique 863
transcripts (Figure 8). Waterlogged conditions increase the risk of pathogen infection in 864
plants (Tamang and Fukao. 2015). Accordingly, rice in paddy fields have protection 865
mechanisms that prevent damage rendering them vulnerable to pathogens (Hsu et al., 866
2013). Therefore, these C9285-specific genes might function as a pathogen defense 867
pathway during partial long-term submergence in C9285 plants. 868
Our studies identified genotype-specific responsive genes to submergence in 869
C9285 plants and assumed that the putative key genes would be associated with 870
submergence-induced physiological responses in C9285 plants. Furthermore, we 871
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40
showed that ethylene is one of the main drivers of submergence responses and JA is a 872
new negative regulator of submergence-induced internode elongation in C9285 plants. 873
The network involving submergence-induced changes and genetic factors complexly 874
regulate underwater elongation and adaptation in deepwater rice. 875
876
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41
877
METHODS 878
Plant material and cultivation 879
A deepwater rice cultivar (C9285, Oryza sativa) and a non-deepwater rice cultivar 880
(Taichung 65, T65, Oryza sativa ssp. Japonica) were used. Rice seeds were incubated 881
at 60˚C for 10 min followed by pre-germination at 29˚C in water for 3 to 4 days. 882
Afterwards, germinated seeds were transferred to plastic pots containing soil mixture 883
(Mikawa Baido, AICHI Mederu, Nishio, JAPAN) and grown in a greenhouse in Nagoya, 884
Japan in June with a natural light cycle of ca. 14 h light / 10 h dark. For deepwater 885
treatment, rice seedlings that reached the indicated leaf stages (4LS and 6LS) were 886
completely submerged for 1, 3, 6, 12 and 24 h (Supplemental Figure 1A). To avoid 887
differences in gene expression between samples due to circadian rhythms, 888
submergence treatments were initiated at different times of the day and all samples 889
were collected in the afternoon, although varying durations of underwater- and above 890
water photosynthesis causes change in the availability of photosynthates. After 891
submergence treatment, 5 mm of the shoot base region containing internodes, nodes, 892
the shoot apex and basal regions of leaves were sampled and rapidly frozen in liquid 893
nitrogen and stored at -80˚C until RNA extraction (Supplemental Figure 1B). 894
895
RNA extraction, sequencing and read mapping 896
For each RNA extraction frozen tissues from one individual plant were homogenized 897
and up to 100 mg were used. Total RNA of each sample was isolated using the RNeasy 898
Plant Mini Kit (Qiagen, Hilden, Germany) with the RNase-Free DNase Set (Qiagen). 899
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42
RNA purity was checked using a NanoDrop spectrophotometer (Thermo-Fisher) and 900
RNA was quantified using a QuantiFluor RNA system (Promega) and an EnSpire 901
Multimode Plate Reader (PerkinElmer). For HiSeq library construction, 2 µg of total RNA 902
was used with the llumina TruSeq RNA Sample Preparation Kit v2 (Illumina) according 903
to the manufacturer's instructions. Agencourt AMPure XP beads (Beckman Coulter) 904
were used to remove small DNA fragments. The clustering of index-coded samples was 905
performed on a cBot Cluster Generation System using the TruSeq SR Cluster Kit v2-906
cBot-GA (Illumia) and the TruSeq SBS Kit v5-GA (Illumia). After cluster generation, the 907
library preparations were sequenced on an Illumina Genome Analyzer IIx and 36 bp 908
single-ended reads were generated. Reads were mapped to the IRGSP 1.0 reference 909
transcripts of Oryza sativa ssp. Japonica cv. Nipponbare (Goff et al., 2002) using bowtie 910
(version 0.12.7) (Langmead et al., 2009) with the “—all –best –strata” options 911
(Supplemental Table 1) and read counts were quantified using PostgreSQL and a 912
custom PHP script. 913
914
Data analysis 915
Statistical data analysis was performed using R. The “edgeR” package was used to 916
normalize raw count data and generate counts per million (cpm) values. (Robinson et 917
al., 2010). Transcripts with less than 10 averaged counts in at least 1 condition were 918
removed from the dataset and only the strongest expressed isoform per transcript was 919
used for analysis. To determine differentially expressed genes, a negative binominal 920
generalized log-linear model was used (function “glmFit”) with each genotype and time 921
point after submergence defined as one group. Then, likelihood-ratio tests (function 922
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43
“glmLRT”) were performed to compare between groups or to test for interactions 923
between genotype and submergence treatment. The Bonferoni-Holm method was used 924
to correct for multiple testing (function “topTags”). PCA was performed using the 925
“prcomp” function with scaled and centered cpm data as the input. k-means clustering 926
was performed using the “MBClusterSeq” package with a negative binomial model and 927
the EM algorithm (Si et al., 2014). The number of clusters was varied between 10 and 928
100 in intervals of 10 and empirically k = 40 (for all samples) or k = 20 (for samples from 929
one genotype only) was chosen as the most appropriate number of clusters. 930
Hierarchical clustering of transcription factor genes was performed using the “dist” and 931
“hclust” functions. The distance matrix was calculated using Euclidian distance and 932
clustering was performed using the “average” algorithm. 933
Gene set enrichment analysis was based on the MAPMAN ontology and 934
mappings (RAPDB locus ID to MAPMAN bin) were obtained from 935
http://www.mapman.gabipd.org (Ramsak et al., 2014). Significant enrichment of bins 936
was determined using Fisher’s Exact test and corrections for multiple testing were done 937
by the Bonferroni-Holm method using the R functions “fisher.test” and “p.adjust”, 938
respectively. Separate analyses were performed for the first three hierarchy levels of the 939
MAPMAN ontology. 940
Metabolic maps were based on a combination of RAPDB, KEGG (Kanehisa et 941
al., 2015), MAPMAN and in-house annotations. Data visualization was performed using 942
ggplot2 (Wickham, 2009). 943
944
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44
ABA and GA3 treatments of whole plants 945
Germinated seeds of C9285 plants were sown in plastic pots filled with soil and then 946
grown in a phytotron at 25˚C with a 14-h photoperiod. When the plants were grown at 947
the 4 LS, they were transferred to new plastic containers for hormone treatment. For 948
hormone treatment, plants were watered with either 10 µM ABA (Sigma-Aldrich), 10 µM 949
Gibberellin A3 (Wako) or a combination of both into the containers. The water level in 950
each container was controlled to keep the hormone concentration during the treatment. 951
Plant height and internode length were measured after 18-day treatment. Internode 952
length was calculated using the total length of all internodes. 953
954
JA treatment of whole plants during submergence 955
Germinated seeds of C9285 plants were sown in plastic pots filled with soil and then 956
grown in a controlled environment chamber at 25˚C with a 14 h photoperiod. When the 957
plants reached the 6 LS they were submerged in water with or without 50 µM methyl 958
jasmonate (Wako) for 3 days. Total internode length was calculated as the sum of the 959
length of all internodes. 960
961
Measurement of plant hormone contents 962
The concentrations of endogenous hormones were measured using UPLC-MS/MS 963
(UPLC-Xevo TQ-S; Waters, Maple Street, Milford, MA, USA) as described in Kojima et 964
al. (2009). 965
966
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45
Measurement of lignin content 967
Nodes and internodes were sampled from C9285 and T65 plants at the 6LS or 7LS 968
before and after submergence treatment for 2 days. Lignin content was determined by 969
the thio-glycolic acid method according to Suzuki et al. (2009). 970
971
Promoter motif enrichment analysis 972
Transcripts were clustered into 6 groups based on expression in C9285 and T65 plants 973
(6LS) at 0 h, 1 h, 3 h, 6 h, 12 h and 24 h after submergence using k-means clustering 974
as described above. For tentative construction of a C9285 genome, all reads obtained 975
from whole-genome sequencing of C9285 were mapped against the IRGSP-1.0 976
pseudomolecules using bwa-mem with the -M option (Li and Durbin, 2009). Mapped 977
reads were re-aligned using RealignerTargetCreator and indelRealigner from the GATK 978
software suite (DePristo et al., 2011). To identify SNPs and INDELs, UnifiedGenotyper 979
of GATK was used with the -glm BOTH option. The C9285 genome sequence was 980
tentatively constructed by modifying the IRGSP-1.0 genome with the identified variants 981
of C9285 by custom Perl scripts. DNA sequences 1 kb upstream of the translational 982
start sites from the C9285 genome were regarded as promoter regions and used for 983
motif enrichment analysis. CENSOR was used to mask low-complexity regions in the 984
promoter sequences (Kohany et al., 2006). The MEME suite was used to find enriched 985
DNA sequence motifs using following parameters: -dna -nmotifs 10 -maxw 10 (Bailey 986
and Elkan, 1994). 987
988
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46
Accession numbers 989
All reads used in this manuscript can be found in the DNA Database of Japan (DDBJ) 990
under bioproject PRJDB5294 (C9285 RNA-Seq reads) and bioproject PRJDB5300 991
(C9285 genomic reads). 992
993
SUPPLEMENTAL DATA 994
Supplemental Figure 1. Schematic overview of the experimental setup and 995
transcriptome sequencing. 996
Supplemental Figure 2. Significance analysis using a generalized log-linear model. 997
Supplemental Figure 3. Expression of genes related to ethylene, gibberellin and 998
abscisic acid signaling during submergence. 999
Supplemental Figure 4. Overview of MapMan visualization of differentially expressed 1000
genes in C9285 plants after 1 h of submergence. 1001
Supplemental Figure 5. Overview of MapMan visualization of differentially expressed 1002
genes in C9285 and T65 plants under non-submerged condition. 1003
Supplemental Figure 6. Expression of lignin biosynthesis genes during submergence. 1004
Supplemental Figure 7. Clustering of transcription factor genes according to expression 1005
in C9285 relative to T65 plants. 1006
Supplemental Figure 8. Submergence-induced AP2/EREBP family genes in C9285 1007
plants. 1008
Supplemental Figure 9. Enriched sequence motifs in the promoters of genes that are 1009
differentially expressed in C9285 plants. 1010
Supplemental Figure 10. Analysis pipeline to detect novel C9285 transcripts. 1011
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47
Supplemental Figure 11. Submergence responses related to plant hormones 1012
Supplemental Figure 12. Isolation of genes specifically induced by submergence in 1013
C9285 4LS plants. 1014
Supplemental Figure 13. Expression of Group VII ERF genes during submergence. 1015
Supplemental Figure 14. A molecular model for the submergence response in the 1016
deepwater rice C9285. 1017
Supplemental Figure 15. Expression of light signaling genes during submergence. 1018
1019
Supplemental Table 1. Summary of read mapping statistics. 1020
Supplemental Table 2. Number of genes with significantly different expression in 1021
pairwise comparisons. 1022
Supplemental Table 3. Enriched MAPMAN bins among genes preferentially expressed 1023
in C9285 or T65 plants. 1024
Supplemental Table 4. Enriched MAPMAN bins among genes induced or repressed by 1025
submergence in either genotype. 1026
Supplemental Table 5. Response to submergence of rice ERF subfamily genes in 1027
C9285 plants. 1028
1029
Supplemental Results 1030
Supplemental Methods 1031
Supplemental References 1032
1033
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48
Supplemental Data Set 1. Gene expression data, annotations and results of whole 1034
transcriptome analysis. 1035
Supplemental Data Set 2. Genes specifically or preferentially expressed in C9285 1036
samples. 1037
Supplemental Data Set 3. Genes specifically or preferentially expressed in T65 1038
samples. 1039
Supplemental Data Set 4. Genes with submergence-induced expression in C9285 1040
samples. 1041
Supplemental Data Set 5. Genes with submergence-induced expression in T65 1042
samples 1043
Supplemental Data Set 6. Genes with submergence-repressed expression in C9285 1044
samples. 1045
Supplemental Data Set 7. Genes with submergence-repressed expression in T65 1046
samples. 1047
Supplemental Data Set 8. Analyses of transcription factor-encoding genes. 1048
Supplemental Data Set 9. List of 189 genes specifically expressed in C9285 plants. 1049
Supplemental Data Set 10. Expression of genes in de novo assembled C9285 genomic 1050
regions. 1051
Supplemental Data Set 11. 36 genes responding to submergence in C9285 at the 6 1052
leaf-stage, but not in C9285 at the 4 leaf-stage. 1053
Supplemental Data Set 12. C9285 unique genomic contigs. 1054
Supplemental Data Set 13. C9285 unique transcripts. 1055
Supplemental Data Set 14. C9285 unique proteins. 1056
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49
1057
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50
ACKNOWLEDGMENTS 1058
We thank Dr. KO Hirano for assisting with lignin quantification and Dr. MASAHIRO 1059
FUJITA for providing C9285 genomic sequencing data. Seeds of C9285 used in this 1060
study was distributed from the National Institute of Genetics supported by the National 1061
Bioresource Project, AMED, JAPAN. 1062
1063
1064
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51
1065
FIGURE LEGENDS 1066
1067
Figure 1. Submergence response of deepwater rice and non-deepwater rice. 1068
(A) Deepwater rice can survive and escape from submerged condition by rapid 1069
elongation of stems (internodes) and leaves while non-deepwater rice cannot 1070
elongate internodes during submergence. (B) Principal component analysis of 18 1071
RNA-Seq samples from C9285 and T65 submerged at different leaf stages (LS) 1072
and time points. A plot of all transcriptome samples along the first two principal 1073
components (PC) is shown. The percentage of variation explained is indicated at 1074
each axis. Colors indicate samples from different genotypes and LS. Each data 1075
point represents averaged data from three independent time series and one 1076
individual plant was sampled for each data point.. 1077
1078
Figure 2. Clustering analysis of the transcriptome of C9285 and T65 plants after 1079
submergence. 1080
Heatmap representations of expression data from selected clusters in both 1081
C9285 and T65 at six-leaf stage (C9286 6LS and T65 6LS) (A), and from clusters 1082
only in C9285 6LS (B) or T65 6LS (C) plants are shown. The clusters in the 1083
figure derived from Supplemental Dataset S1 were manually arranged. Rows 1084
represent clusters of genes generated by k-means clustering. Columns represent 1085
samples from different time points after submergence. Colors represent the 1086
average expression profile for each cluster with red showing high and blue 1087
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52
showing low expression, respectively. Before averaging within each cluster, 1088
expression of each gene was normalized to its average expression across all 1089
samples and transformed to log2 values. Numbers on the left side of each panel 1090
show the assigned cluster IDs and the number of genes in each cluster is in 1091
parenthesis. The total number of clusters was k = 40 in (A) and k = 20 in (B) and 1092
(C). 1093
1094
Figure 3. Ethylene, gibberellin, and abscisic acid metabolism during 1095
submergence. 1096
Schematic overview of ethylene (A), gibberellin (GA) (B) and abscisic acid (ABA) 1097
(C) metabolism alongside heatmaps showing expression of relevant genes are 1098
shown. Each row represents one gene, columns represent samples from different 1099
time points after submergence and colors represent gene expression levels as 1100
log2 transformed counts per million values (cpm). Lower levels of expression are 1101
represented in blue and higher expression in yellow. ACS, ACC-synthase; AAO3, 1102
ABA-aldehyde oxidase; ABA8ox, ABA-8’ oxidase; ACC, 1-aminocyclopropane-1-1103
carboxylic acid; ACO, ACC-oxidase; CPS, copalyl-phosphate synthase; CYP714, 1104
cytochrome P714; GAXox, GA-X oxidase; GGDP, geranyl-geranyl diphosphate; 1105
KAO, ent-kaurenoic acid oxidase; KO, ent-kaurene oxidase; KS, ent-kaurene 1106
synthase; NCED, 9-cis-epoxycarotenoid dioxygenase; SAM, S-adenosyl 1107
methionine; ZEP1, zeaxanthin epoxidase 1. Asterisks indicates genes with 1108
significant difference (FDR < 0.05) at more than 4 time points between C9285 1109
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53
and T65 samples and < or > indicate the direction of the difference relative to 1110
C9285. (D) Effect of ABA and GA3 on plant height and total internode length. 1111
C9285 4LS plants were grown in shallow-water containing 10 µM GA3 and/or 10 1112
µM ABA for 18 days. Bars represent the average of at least seven biological 1113
replicates and error bars show standard errors. Asterisks show significant 1114
differences (P < 0.05) between the indicated treatments as calculated by 1115
Student’s t tests. 1116
1117
Figure 4. Jasmonic acid metabolism during submergence. 1118
(A) Schematic overview of jasmonic acid (JA) metabolism alongside heatmaps 1119
showing expression of relevant genes are shown. Each row represents one 1120
gene, columns represent samples from different time points after submergence 1121
and colors represent gene expression levels as log2 transformed counts per 1122
million values (cpm). Lower levels of expression are represented in blue and 1123
higher expression in yellow. FDA, fatty acid desaturase; DAD1, defective in 1124
anther dehiscence1; PLA, phospholipase A1; LOX, lipoxygenase; 13(S)-HPOT, 1125
(13S)-hydroperoxyoctadecatrienoic acid; AOS, allene oxide synthase; 12, 13-1126
EOT, 12,13(S)-epoxy-octadecatrienoic acid; AOC, allene oxide cyclase; OPDA, 1127
cis-(+)-12-oxophytodienoic acid; OPR, 12-oxo-phytodienoic acid reductase; 1128
OPC-8, OPC-8, 3-oxo-2-(2’-pentenyl)-cyclopentane-1-octanoic acid; OPCL1, 1129
acyl-activating enzyme; ACX, acyl-CoA oxidase; MFP, multifunctional protein; 1130
KAT, 3-keto-acyl-CoA thiolase; TS2, tasselseed2; JA-CoA, jasmonoyl-CoA; (+)-7-1131
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iso-JA, (+)-7-iso-jasmonoyl; JAR1, jasmonate resistant1; JA-lle, (+)-7-iso-1132
jasmonoly-L-isoleucine; CYP94, cytochrome P94. Asterisks indicates genes with 1133
significant difference (FDR < 0.05) at more than 4 time points between C9285 1134
and T65 samples and < or > indicate the direction of the difference relative to 1135
C9285. (B) Endogenous JA level in the shoot base regions of C9285 and T65 1136
plants during submergence for 24 hours. Bars represent the average of at least 1137
five biological replicates and error bars represent standard errors. Asterisk show 1138
significant difference (P < 0.05) between C9285 and T65 samples as calculated 1139
by Student’s t tests. (C) Jasmonic acid inhibits internode elongation during 1140
submergence. C9285 6LS plants were submerged under water containing 50 µM 1141
metyl jasmonate (Me-JA) for 3 days. Bars represent the average of at least 1142
twelve biological replicates and error bars show standard errors. Asterisk show 1143
significant difference (P < 0.05) between the indicated treatments as calculated 1144
by Student’s t tests. 1145
1146
Figure 5. Expression of trehalose metabolism-related genes during 1147
submergence. 1148
(A) Schematic overview of the trehalose metabolic pathway. Glu6P, glucose-6-1149
phosphate; Tre6P, trehalose-6-phosphate; UDPG, UDP-glucose. (B) to (D) 1150
Expression of genes involved in trehalose metabolism during submergence in 1151
C9285 6LS (black) and T65 6LS (orange) plants at the indicated time points after 1152
submergence. Data points show expression levels as average cpm in three 1153
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55
biological replicates and error bars show standard deviation. (B) TPS; trehalose-1154
6-phosphate synthase, (C) TPP; trehalose-6-phosphate phosphatase, (D) TRE; 1155
trehalase. Black and orange asterisks indicate significant differences (P < 0.05) 1156
from 0 h at each time point for C9285 and T65 samples, respectively. Daggers 1157
indicate significant differences (FDR < 0.05) between C9285 and T65 samples. 1158
P-values were calculated using likelihood ratio tests and corrected for multiple 1159
testing by the Bonferoni-Holm method. 1160
1161
Figure 6. Expression of fermentation-related genes during submergence. 1162
(A) Schematic overview of three fermentation pathways. (B) Expression of genes 1163
related to fermentation during submergence in 6LS C9285 (black) and 6LS T65 1164
(orange) plants at the indicated time points after submergence is shown. Data 1165
points show expression levels as average cpm in three biological replicates and 1166
error bars show standard deviation. Panels have been arranged to reflect the 1167
different possibilities of anaerobic energy production. PEP; 1168
phosphoenolpyruvate, ADH; aldehyde dehydrogenase, AlaAT; alanine-1169
aminotransferase, ALDH; alcohol dehydrogenase, LDH; lactate dehydrogenase, 1170
PDC; pyruvate decarboxylase. Black and orange asterisks indicate significant 1171
differences (P < 0.05) from 0 h at each time point for C9285 and T65 samples, 1172
respectively. Daggers indicate significant differences (P < 0.05) between C9285 1173
and T65 samples. P-values were calculated using likelihood ratio tests and 1174
corrected for multiple testing by the Bonferoni-Holm method. 1175
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56
1176
Figure 7. Effect of submergence on the expression of cell wall formation-related 1177
genes. 1178
(A) Expression pattern of cell wall-related genes during 24 h of submergence. 1179
The gene expression levels in C9285 6LS and T65 6LS samples are indicated by 1180
log2-fold changes at each time point (0 h, 1 h, 3 h, 12 h and 24 h) relative to that 1181
of T65 samples before submergence. Genes with a maximal cpm value of more 1182
than 15 are shown. AGP, arabinogalactan protein; PME, pectin esterase; XTH, 1183
xyloglucan endotransglycosylases/hydrolase. (B) Changes in expression of 11 1184
coniferyl/sinapyl alcohol dehydrogenase (CAD) genes during submergence for 1185
24 h. Data points show expression levels as average cpm in three biological 1186
replicates and error bars show standard deviation. (C) Sampled regions of 1187
internodes for lignin quantification. C9285 plants at the seven-leaf stage (7LS) 1188
that have already formed internodes were submerged for 2 days (2 d). Photos of 1189
stems before (0 d) and after (2 d) submergence treatment of C9285 plants at the 1190
7LS are shown. Red arrowheads indicate stem nodes. (D, E) Lignin content in 1191
the nodes and internodes before (D) and after (E) 2 d submergence of C9285 1192
plants at 7LS. Bars represent averages of at least six biological replicates and 1193
error bars represent standard errors. Different letters indicate significant (P < 1194
0.05) differences according to the Tukey-Kramer test. 1195
1196
Figure 8. Submergence-induced transcripts from C9285-unique loci. 1197
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Expression from selected loci which are presumably absent in the IRGSP1.0 1198
reference genome is shown. Each row represents one locus, columns represent 1199
samples from different time points after submergence and colors represent gene 1200
expression levels as log2 transformed counts per million values (cpm) normalized 1201
to the average expression in all samples of different time points. Genes that have 1202
an at least two-fold increase in expression after submergence in C9285 6 LS 1203
plants are shown. Complete expression data from C9285-unique transcripts can 1204
be found in Supplemental Dataset 10 and sequence data is provided in 1205
Supplemental Datasets 12 to 14. 1206
1207
1208
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A
B
Shallow water Deep water
Deepwater rice Non-deepwater rice Deepwater rice Non-deepwater rice
Figure 1. Submergence response of deepwater rice and non-deepwater rice. (A) Deepwater rice can survive and escape from submerged condition by rapid elongation of stems (internodes) and leaves while non-deepwater rice cannot elongate internodes during submergence. (B) Principal component analysis of 18 RNA-Seq samples from C9285 and T65 submerged at different leaf stages (LS) and time points. A plot of all transcriptome samples along the first two principal components (PC) is shown. The percentage of variation explained is indicated at each axis. Colors indicate samples from different genotypes and LS. Each data point represents averaged data from three biological replicates.
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Figure 2. Clustering analysis of the transcriptome of C9285 and T65 plants after submergence. Heatmap representations of expression data from selected clusters in both C9285 and T65 at six-leaf stage (C9286 6LS and T65 6LS) (A), and from clusters only in C9285 6LS (B) or T65 6LS (C) plants are shown. The clusters in the figure derived from Supplemental Dataset S1 were manually arranged. Rows represent clusters of genes generated by k-means clustering. Columns represent samples from different time points after submergence. Colors represent the average expression profile for each cluster with red showing high and blue showing low expression, respectively. Before averaging within each cluster, expression of each gene was normalized to its average expression across all samples and transformed to log2 values. Numbers on the left side of each panel show the assigned cluster IDs and the number of genes in each cluster is in parenthesis. The total number of clusters was k = 40 in (A) and k = 20 in (B) and (C).
T65repressed
repressed
T65 6LS
C17 (159)C13 (871)C5 (215)C3 (1868)C1 (1450)
C2 (514)
induced
repressed0 1 3 6 12 24cl
uste
r ID
(no.
of g
enes
)
-2 -1 0 1
C9285 6LS
B16 (1035)B12 (1063)B11 (354)B9 (421)B6 (331)
B17 (159)B15 (553)B8 (1201)B7 (1969)
induced
0 1 3 6 12 24submergence time point (h)
clus
ter I
D (n
o. o
f gen
es)
-1 0 1 2
A B
C
C9285 6LS T65 6LS
C9285
induced
0 1 3 6 12 24 0 1 3 6 12 24
A11 (121)A4 (298)A1 (600)
A30 (174)A29 (127)A22 (348)A14 (193)A6 (211)A2 (152)
A36 (375)A32 (605)A16 (739)A13 (719)A8 (245)
A25 (371)A20 (282)A19 (1026)A10 (598)
clus
ter I
D (n
o. o
f gen
es)
-2 0 2 4
average log2 FCrelative to row mean
average log2 FCrelative to row mean
average log2 FCrelative to row mean
submergence time point (h)submergence time point (h)
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Figure 3. Ethylene, gibberellin, and abscisic acid metabolism during submergence.Schematic overview of ethylene (A), gibberellin (GA) (B) and abscisic acid (ABA) (C) metabolism alongside heatmaps showing expression of relevant genes are shown. Each row represents one gene, columns represent samples from different time points after submergence and colors represent gene expression levels as log2transformed counts per million values (cpm). Lower levels of expression are represented in blue and higher expression in yellow. ACS, ACC-synthase; AAO3, ABA-aldehyde oxidase; ABA8ox, ABA-8’ oxidase; ACC, 1-aminocyclopropane-1-carboxylic acid; ACO, ACC-oxidase; CPS, copalyl-phosphate synthase; CYP714, cytochrome P714; GAXox, GA-X oxidase; GGDP, geranyl-geranyl diphosphate; KAO, ent-kaurenoic acid oxidase; KO, ent-kaurene oxidase; KS, ent-kaurene synthase; NCED, 9-cis-epoxycarotenoid dioxygenase; SAM, S-adenosylmethionine; ZEP1, zeaxanthin epoxidase 1. Asterisks indicates genes with significant difference (FDR < 0.05) at more than 4 time points between C9285 and T65 samples. Among genes with asterisks, < or > indicates the lower or higher gene expression levels in C9285 plants than that in T65 plants, respectively. (D) Effect of ABA and GA3 on plant height and total internode length. C9285 4LS plants were grown in shallow-water containing 10 µM GA3 and/or 10 µM ABA for 18 days. Bars represent the average of at least seven biological replicates and error bars show standard errors. Asterisks show significant differences (P < 0.05) between the indicated treatments as calculated by Student’s t tests.
C9285 T65ZEP1
ABA4 * >
NCED1 * >NCED2NCED5
ABA2 * <
ABA3AAO3;3AAO3;2
ABA8ox1ABA8ox2ABA8ox3
0 1 3 6 12 24 0 1 3 6 12 24
SAM ACC Ethylene
tota
l int
erno
de le
ngth
(cm
)
plan
t hei
ght
(cm
)
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20
40
60
80
100
0
5
10
15
20
25
* *
A
C
BACS
(rate-limiting)
D
β-carotene
zeaxanthin
antheraxanthin
violaxanthin
9-cis-neozanthin
neoxanthin
9-cis-violazanthin
xanthoxin
ABA-aldehyde
ABA
8’-hydroxy ABA
ACO
ZEP1
ZEP1
ABA4
NCED (rate-limiting )
ABA2
ABA3/AAO
ABA8ox
GGDP
ent-CDP
ent-Kaurene
ent-kaurenoic acid
KS
KO
CPS
GA12
GA15
GA24
GA9
GA53
GA44
GA19
GA20
GA4 GA1
GA51 GA34GA29, GA8
Non
-13-
OH
pat
hway
KAOGA13ox
GA20ox
GA3ox
GA2ox
Early-13-O
H pathw
ay
expression level (log2 cpm)
C9285 T65ACS6
ACO1ACO2 * >ACO3ACO4ACO5ACO6ACO7 * >
0 1 3 6 12 24 0 1 3 6 12 24
submergence time point (h)
submergence time point (h)
submergence time point (h)
expression level (log2 cpm)
expression level (log2 cpm)
C9285 T65CPSKS * >KO2 * <KO1a * <KAO
GA13ox/CYP714B1 GA13ox/CYP714B2
GA20ox1GA20ox2 * >GA20ox4
GA3ox2 * >
GA2ox1GA2ox3GA2ox4GA2ox6GA2ox7GA2ox8GA2ox9GA2ox10
OsGA2ox110 1 3 6 12 24 0 1 3 6 12 24
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Figure 4. Jasmonic acid metabolism during submergence. (A) Schematic overview of jasmonic acid (JA) metabolism alongside heatmaps showing expression of relevant genes are shown. Each row represents one gene, columns represent samples from different time points after submergence and colors represent gene expression levels as log2 transformed counts per million values (cpm). Lower levels of expression are represented in blue and higher expression in yellow. FDA, fatty acid desaturase; DAD1, defective in anther dehiscence1; PLA, phospholipase A1; LOX, lipoxygenase; 13(S)-HPOT, (13S)-hydroperoxyoctadecatrienoic acid; AOS, allene oxide synthase; 12, 13-EOT, 12,13(S)-epoxy-octadecatrienoic acid; AOC, allene oxide cyclase; OPDA, cis-(+)-12-oxophytodienoic acid; OPR, 12-oxo-phytodienoic acid reductase; OPC-8, OPC-8, 3-oxo-2-(2’-pentenyl)-cyclopentane-1-octanoic acid; OPCL1, acyl-activating enzyme; ACX, acyl-CoA oxidase; MFP, multifunctional protein; KAT, 3-keto-acyl-CoA thiolase; TS2, tasselseed2; JA-CoA, jasmonoyl-CoA;(+)-7-iso-JA, (+)-7-iso-jasmonoyl; JAR1, jasmonate resistant1; JA-lle, (+)-7-iso-jasmonoly-L-isoleucine; CYP94, cytochrome P94. Asterisks indicates genes with significant difference (FDR < 0.05) at more than 4 time points between C9285 and T65 samples. < or > indicates the lower or higher gene expression levels in C9285 plants than that in T65 plants, respectively. (B) Endogenous JA level in the shoot base regions of C9285 and T65 plants during submergence for 24 hours. Bars represent the average of at least five biological replicates and error bars represent standard errors. Asterisk show significant difference (P < 0.05) between C9285 and T65 samples as calculated by Student’s t tests. (C) Jasmonic acid inhibites internode elongation during submergence. C9285 6LS plants were submerged under water containing 50 µM metyl jasmonate (Me-JA) for 3 days. Bars represent the average of at least twelve biological replicates and error bars show standard errors. Asterisk show significant difference (P < 0.05) between the indicated treatments as calculated by Student’s t tests.
OPR3
Membrane lipids
13(S)-HPOT
12, 13-EOT
OPDA
JA-IIe
(+)-7-iso-JA
LOX
AOS
AOC
α-Linolenic acid (LA)
JA-CoAThioesterase
JAR1
12OH-JA-lle
12COOH-JA-lle
CYP94B
β-ox
idat
ion
JA (p
mol
/ gFW
)
submergence time point (h)
expression level (log2 cpm)
B
A
0
100
200
300
400
500
600T65
C9285
submergence time point (h)
0 6 12 24
DAD/PLA
C9285 T65DAD1;3 PLA1
DAD1;4* >
LOX2;2* >LOX2;5
OS03G0699700OS03G0700700* >OS04G0447100OS05G0304600OS05G0355800
AOS2* >
AOC3AOC* >
OPR7OPCL1
ACXOaAIM1
KATTS2* <
Thioesterase
JAR1JAR2* >
CYP94C3CYP94C4* >
0 1 3 6 12 24 0 1 3 6 12 24
CYP94C
C
0
2
4
6
8
10
12
14
Control_DW DW_JA 50uM
Tota
l int
erno
de le
ngth
(cm
)
*
control Me-JA
submergence for 3 days
*
OPC-8OPCL1ACXMFPKATTS2
Linolenic acidFAD
www.plantphysiol.orgon June 23, 2020 - Published by Downloaded from Copyright © 2018 American Society of Plant Biologists. All rights reserved.
Figure 5. Expression of trehalose metabolism-related genes during submergence.(A) Schematic overview of the trehalose metabolic pathway. Glu6P, glucose-6-phosphate; Tre6P, trehalose-6-phosphate; UDPG, UDP-glucose. (B) to (D) Expression of genes involved in trehalose metabolism during submergence in C9285 6LS (black) and T65 6LS (orange) plants at the indicated time points after submergence. Data points show expression levels as average cpm in three biological replicates and error bars show standard deviation. (B) TPS; trehalose-6-phosphate synthase, (C) TPP; trehalose-6-phosphate phosphatase, (D) TRE; trehalase. Black and orange asterisks indicate significant differences (P < 0.05) from 0 h at each time point for C9285 and T65 samples, respectively. Daggers indicate significant differences (FDR < 0.05) between C9285 and T65 samples. P-values were calculated using likelihood ratio tests and corrected for multiple testing by the Bonferoni-Holm method.
TPS2TPS1 TPS3 TPS4 TPS6
TPS7 TPS8 TPS9 TPS10
TPP3 TPP5 TPP6 TPP7
TPS
UDPG + Galc6P
TPP
Tre6P
Trehalose
TRE
2 x Glucose
TPP1 TPP2 TPP11
0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 240
10
20
0
1
2
3
0
10
20
30
0.0
0.2
0.4
0.6
0.8
0
1
2
3
0
2
4
0
50
100
150
submergence time point (h)
expr
essi
on (c
pm)
C9285 6LS T65 6LS
TPP
TPS12 TPS13 TPS14
TPS11
0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24
0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24
0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 240
100
200
300
01020304050
050
100150200
0
10
20
30
0
50
100
150
0255075
100
0
10
20
30
0255075
100
0255075
100
0
10
20
30
0
50
100
150
0
50
100
150
010203040
submergence time point (h)
expr
essi
on (c
pm)
TPSA B
C DTrehalase
submergence time point (h)
expr
essi
on (c
pm)
TRE
0 1 3 6 12 240
3
6
9
* * **
**
* **
*
* ** * * * * * * ** * *
* ** ** *
*** **
* * *
* *** *
* *
**
**
* *** *
* ** **
* *
**
*
†
† †
†
†
† †††† ††††
†
† † † *
*
*
**** **
*† * * **
* **
**†
*
** *** *
† † † †
†* * *
***
**
*
*
† † ††
†
†* * *
***
**
*
*
† † ††
†
† * * *
***
**
*
*
† † ††
†
†
**
*
***
*
* *
*
†
†
†
†
†
* **
**
* ** *
*
**† †
††
* *
** *
*
†
* ***
**
**
† ††
†
***
**
*
TPS2TPS1 TPS3 TPS4 TPS6
TPS7 TPS8 TPS9 TPS10
TPP3 TPP5 TPP6 TPP7
TPS
UDPG + Glu6P
TPP
Tre6P
Trehalose
TRE
2 x Glucose
TPP1 TPP2 TPP11
0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 240
10
20
0
1
2
3
0
10
20
30
0.0
0.2
0.4
0.6
0.8
0
1
2
3
0
2
4
0
50
100
150
submergence time point (h)
expr
essi
on (c
pm)
C9285 6LS T65 6LS
TPP
TPS12 TPS13 TPS14
TPS11
0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24
0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24
0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 24 0 1 3 6 12 240
100200300
01020304050
050
100150200
0
10
20
30
0
50
100
150
0255075
100
0
10
20
30
0255075
100
0255075
100
0102030
0
50
100
150
0
50
100
150
010203040
submergence time point (h)
expr
essi
on (c
pm)
TPSA B
C DTrehalase
submergence time point (h)
expr
essi
on (c
pm)
TRE
0 1 3 6 12 240
3
6
9
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Figure 6. Expression of fermentation-related genes during submergence.(A) Schematic overview of three fermentation pathways. (B) Expression of genes related to fermentation during submergence in 6LS C9285 (black) and 6LS T65 (orange) plants at the indicated time points after submergence is shown. Data points show expression levels as average cpm in three biological replicates and error bars show standard deviation. Panels have been arranged to reflect the different possibilities of anaerobic energy production. PEP; phosphoenolpyruvate, ADH; aldehyde dehydrogenase, AlaAT; alanine-aminotransferase, ALDH; alcohol dehydrogenase, LDH; lactate dehydrogenase, PDC; pyruvate decarboxylase. Black and orange asterisks indicate significant bdifferences (P < 0.05) from 0 h at each time point for C9285 and T65 samples, respectively. Daggers indicate significant differences (P < 0.05) between C9285 and T65 samples. P-values were calculated using likelihood ratio tests and corrected for multiple testing by the Bonferoni-Holm method.
†*
*
**
*
*
*
* †
†
††** * *
*†
††
*
* * * *
* * *
**
*
† † †
* **
**
* * * **
** *
* *†
†
† †
†
†
†
†* * *
*†
** *
** *
†† †
† **
** *
* **
*
† †
†* * * *
†
***
* * *
†
† **
†
†*
* *
* * *
†
†**
*
* * **
***
†
††
†
*
* ** *
***
**
**
* ***
*
*
* *
*
***† † †† † †
†
**
** * * *
* * * *
*†
† †
*** *
*** *
**
†
†
†
†
*** * *
** **
†
**†
††
†
* * * **
* *
††
† † †
* * * *
* *† †
* * *
* * * *† †
† † † *† † † †
†
***
† ††
††
www.plantphysiol.orgon June 23, 2020 - Published by Downloaded from Copyright © 2018 American Society of Plant Biologists. All rights reserved.
Figure 7. Effect of submergence on the expression of cell wall formation-related genes. (A) Expression pattern of cell wall-related genes during 24 h of submergence. The gene expression levels in C9285 6LS and T65 6LS samples are indicated by log2-fold changes at each time point (0 h, 1 h, 3 h, 12 h and 24 h) relative to that of T65 samples before submergence. Genes with a maximal cpm value of more than 15 are shown. AGP, arabinogalactan protein; PME, pectin esterase; XTH, xyloglucan endotransglycosylases/hydrolase. (B) Changes in expression of 11 coniferyl/sinapyl alcohol dehydrogenase (CAD) genes during submergence for 24 h. Data points show expression levels as average cpm in three biological replicates and error bars show standard deviation. (C) Sampled regions of internodes for lignin quantification. C9285 plants at the seven-leaf stage (7LS) that have already formed internodes were submerged for 2 days (2 d). Photos of stems before (0 d) and after (2 d) submergence treatment of C9285 plants at the 7LS are shown. Red arrowheads indicate stem nodes. (D, E) Lignin content in the nodes and internodes before (D) and after (E) 2 d submergence of C9285 plants at 7LS. Bars represent averages of at least six biological replicates and error bars represent standard errors. Different letters indicate significant (P < 0.05) differencesaccording to the Tukey-Kramer test.
2nd node 3rd node
B
tota
l lig
nin
cont
ent (
% d
ry w
eigh
t)
D
C
E
1 cm
0 dbasal node
2 d
newly-elongated intermode
non-elongated internode
A
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
basalnode
2nd+3rdnode
non-elongatedinternode
basalnode
2ndnode
non-elongatedinternode
3rdnode
newlyelongatedinternode
2nd node
3rd node
basal node
tota
l lig
nin
cont
ent (
% d
ry w
eigh
t) 0 d 2 d
C9285 6LS T65 6LS C9285 6LS T65 6LSC9285
max cpm
α-expansinβ-expansin
XTH
PME
AGP-like
extensin-like
0 1 3 6 12 24 0 1 3 6 12 24
EXPA6 (23.26)EXPLA3 (25.47)EXPLA2 (28.02)EXPA5 (29.65)EXPLA1 (41.01)EXPA3 (47.24)EXPA2 (66.36)EXPA4 (91.77)EXPA7 (95.97)
EXPB17 (17.14)EXPB16 (18.51)EXPB7 (20.68)EXPB12 (32.76)EXPB6 (42.4)EXPB3 (205.69)EXPB4 (518.98)
XTH12 (7.76)XTH28 (11.53)XTH19 (29.16)XTH2 (31.35)XTH24 (36.15)XTH21 (37.16)XTH1 (45.29)XTH27 (64.75)XTH17 (101.83)XTH3 (140.51)XTH23 (162.11)XTH11 (226.32)XTH10 (460.38)
PME3 (21.62)PME29 (24.53)PME7 (83.85)
FLA4 (20.24)FLA5 (26.73)FLA24 (36.75)FLA11 (41.68)FLA16 (41.91)FLA1 (48.26)FLA2 (51.13)FLA6 (73.41)FLA7 (102.53)FLA3 (130.15)
OS01G0594300 (16.42)OS04G0670100 (18.23)OS02G0138000 (18.46)OS01G0180000 (21.72)OS07G0176500 (24.16)OS05G0180300 (27.48)OS02G0616100 (37.23)OS04G0505200 (90.09)
submergence time point (h)
submergence time point (h)-2 0 2 4
C9285max cpm
A
B C
D E
1 cm
newlyelongated internode
non-elongated internode
2nd node
3rd node
basal nodebasal node
2nd node
3rd node1
cm
DW 0 d DW 2 d
Tota
l lig
nin
cont
ent
(% d
ry w
eigh
t)
012345678
basalnode
2nd+3rdnode
non-elongatedinternode
Tota
l lig
nin
cont
ent
(% d
ry w
eigh
t)
0
1
2
3
4
5
6
7
basalnode
2ndnode
non-elongatedinternode
3rdnode
newlyelongatedinternode
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 240
20
40
60
submergence time point (h)
expr
essi
on (c
pm)
CAD1
CAD2
CAD3
CAD4
CAD6
CAD7
CAD8A
CAD8B
CAD8C
CAD8D
CAD9
DW 0 d DW 2 d
log2 FCrelative to T65 0 h
EXPA11 96EXPA2 92EXPA13 66EXPA5 47EXPA12 41EXPA25 30EXPA6 28EXPA21 25EXPA7 23
EXPB4 519EXPB3 206EXPB6 42EXPB12 33EXPB7 21EXPB16 19EXPB17 17
XTH10 460XTH11 226XTH23 162XTH3 141XTH17 102XTH27 65XTH1 45XTH21 37XTH24 36XTH2 31XTH19 29 submergence time point (h)
submergence time point (h)
C9285 6LS T65 6LSC9285
max cpm
α-e
xpansin
β-e
xpansin
XT
H
PM
EA
GP
-likeexte
nsin
-like
0 1 3 6 12 24 0 1 3 6 12 24
EXPA6 (23.26)EXPLA3 (25.47)EXPLA2 (28.02)EXPA5 (29.65)EXPLA1 (41.01)EXPA3 (47.24)EXPA2 (66.36)EXPA4 (91)EXPA7 (95)
EXPB17 (17.14)EXPB16 (18.51)EXPB7 (20.68)EXPB12 (32.76)EXPB6 (42.4)EXPB3 (205.69)EXPB4 (518.98)
XTH12 (7.76)XTH28 (11.53)XTH19 (29.16)XTH2 (31.35)XTH24 (36.15)XTH21 (37.16)XTH1 (45.29)XTH27 (64.75)XTH17 (101.83)XTH3 (140.51)XTH23 (162.11)XTH11 (226.32)XTH10 (460.38)
PME3 (21.62)PME29 (24.53)PME7 (83.85)
FLA4 (20.24)FLA5 (26.73)FLA24 (36.75)FLA11 (41.68)FLA16 (41.91)FLA1 (48.26)FLA2 (51.13)FLA6 (73.41)FLA7 (102.53)FLA3 (130.15)
OS01G0594300 (16.42)OS04G0670100 (18.23)OS02G0138000 (18.46)OS01G0180000 (21.72)OS07G0176500 (24.16)OS05G0180300 (27.48)OS02G0616100 (37.23)OS04G0505200 (90.09)
-2 0 2 4
C9285A
B C
D E
1 c
m
newlyelongated internode
non-elongated internode
2nd node
3rd node
basal nodebasal node
2nd node
3rd node
1 c
m
DW 0 d DW 2 d
Tota
l lig
nin
conte
nt
(% d
ry w
eig
ht)
012345678
basalnode
2nd+3rdnode
non-elongatedinternode
Tota
l lig
nin
conte
nt
(% d
ry w
eig
ht)
0
1
2
3
4
5
6
7
basalnode
2ndnode
non-elongatedinternode
3rdnode
newlyelongatedinternode
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 240
20
40
60
submergence time point (h)
exp
ress
ion
(cp
m)
CAD1
CAD2
CAD3
CAD4
CAD6
CAD7
CAD8A
CAD8B
CAD8C
CAD8D
CAD9
DW 0 d DW 2 d
log2 FCrelative to T65 0 h
0 1 3 6 12 24
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 24
submergence time point (h)
submergence time point (h)
C9285 6LS T65 6LSC9285
max cpm
α-expansinβ-expansin
XTH
PM
EA
GP
-likeextensin-like
0 1 3 6 12 24 0 1 3 6 12 24
EXPA6 (23.26)EXPLA3 (25.47)EXPLA2 (28.02)EXPA5 (29.65)EXPLA1 (41.01)EXPA3 (47.24)EXPA2 (66.36)EXPA4 (91)EXPA7 (95)
EXPB17 (17.14)EXPB16 (18.51)EXPB7 (20.68)EXPB12 (32.76)EXPB6 (42.4)EXPB3 (205.69)EXPB4 (518.98)
XTH12 (7.76)XTH28 (11.53)XTH19 (29.16)XTH2 (31.35)XTH24 (36.15)XTH21 (37.16)XTH1 (45.29)XTH27 (64.75)XTH17 (101.83)XTH3 (140.51)XTH23 (162.11)XTH11 (226.32)XTH10 (460.38)
PME3 (21.62)PME29 (24.53)PME7 (83.85)
FLA4 (20.24)FLA5 (26.73)FLA24 (36.75)FLA11 (41.68)FLA16 (41.91)FLA1 (48.26)FLA2 (51.13)FLA6 (73.41)FLA7 (102.53)FLA3 (130.15)
OS01G0594300 (16.42)OS04G0670100 (18.23)OS02G0138000 (18.46)OS01G0180000 (21.72)OS07G0176500 (24.16)OS05G0180300 (27.48)OS02G0616100 (37.23)OS04G0505200 (90.09)
-2 0 2 4
C9285A
B C
D E
1 cm
newlyelongated internode
non-elongated internode
2nd node
3rd node
basal nodebasal node
2nd node
3rd node
1 cm
DW 0 d DW 2 d
Tota
l lig
nin
cont
ent
(% d
ry w
eigh
t)
012345678
basalnode
2nd+3rdnode
non-elongatedinternode
Tota
l lig
nin
cont
ent
(% d
ry w
eigh
t)
0
1
2
3
4
5
6
7
basalnode
2ndnode
non-elongatedinternode
3rdnode
newlyelongatedinternode
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 240
20
40
60
submergence time point (h)
expr
essi
on (c
pm)
CAD1
CAD2
CAD3
CAD4
CAD6
CAD7
CAD8A
CAD8B
CAD8C
CAD8D
CAD9
DW 0 d DW 2 d
log2 FCrelative to T65 0 h
0 1 3 6 12 24
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 24
Os01g0880300 84Os10g0407000 25Os01g0312500 22
FLA3 130FLA7 103FLA6 73FLA2 51FLA1 48FLA16 42FLA11 42FLA24 37FLA5 27FLA4 20
Os04g0505200 90Os02g0616100 37Os05g0180300 27Os07g0176500 24Os01g0180000 22Os02g0138000 18Os04g0670100 18Os01g0594300 16
C9Max (cpm)
submergence time point (h)
submergence time point (h)
submergence time point (h)
submergence time point (h)
C9285 6LS T65 6LSC9285
max cpm
α-e
xpansin
β-e
xpansin
XT
H
PM
EA
GP
-likeexte
nsin
-like
0 1 3 6 12 24 0 1 3 6 12 24
EXPA6 (23.26)EXPLA3 (25.47)EXPLA2 (28.02)EXPA5 (29.65)EXPLA1 (41.01)EXPA3 (47.24)EXPA2 (66.36)EXPA4 (91)EXPA7 (95)
EXPB17 (17.14)EXPB16 (18.51)EXPB7 (20.68)EXPB12 (32.76)EXPB6 (42.4)EXPB3 (205.69)EXPB4 (518.98)
XTH12 (7.76)XTH28 (11.53)XTH19 (29.16)XTH2 (31.35)XTH24 (36.15)XTH21 (37.16)XTH1 (45.29)XTH27 (64.75)XTH17 (101.83)XTH3 (140.51)XTH23 (162.11)XTH11 (226.32)XTH10 (460.38)
PME3 (21.62)PME29 (24.53)PME7 (83.85)
FLA4 (20.24)FLA5 (26.73)FLA24 (36.75)FLA11 (41.68)FLA16 (41.91)FLA1 (48.26)FLA2 (51.13)FLA6 (73.41)FLA7 (102.53)FLA3 (130.15)
OS01G0594300 (16.42)OS04G0670100 (18.23)OS02G0138000 (18.46)OS01G0180000 (21.72)OS07G0176500 (24.16)OS05G0180300 (27.48)OS02G0616100 (37.23)OS04G0505200 (90.09)
-2 0 2 4
C9285A
B C
D E
1 c
m
newlyelongated internode
non-elongated internode
2nd node
3rd node
basal nodebasal node
2nd node
3rd node
1 c
m
DW 0 d DW 2 d
Tota
l lig
nin
conte
nt
(% d
ry w
eig
ht)
012345678
basalnode
2nd+3rdnode
non-elongatedinternode
Tota
l lig
nin
conte
nt
(% d
ry w
eig
ht)
0
1
2
3
4
5
6
7
basalnode
2ndnode
non-elongatedinternode
3rdnode
newlyelongatedinternode
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 240
20
40
60
submergence time point (h)
exp
ress
ion
(cp
m)
CAD1
CAD2
CAD3
CAD4
CAD6
CAD7
CAD8A
CAD8B
CAD8C
CAD8D
CAD9
DW 0 d DW 2 d
log2 FCrelative to T65 0 h
0 1 3 6 12 24
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 24
C9Max (cpm)
submergence time point (h)
submergence time point (h)
C9285 6LS T65 6LSC9285
max cpm
α-expansinβ-expansin
XTH
PM
EA
GP
-likeextensin-like
0 1 3 6 12 24 0 1 3 6 12 24
EXPA6 (23.26)EXPLA3 (25.47)EXPLA2 (28.02)EXPA5 (29.65)EXPLA1 (41.01)EXPA3 (47.24)EXPA2 (66.36)EXPA4 (91)EXPA7 (95)
EXPB17 (17.14)EXPB16 (18.51)EXPB7 (20.68)EXPB12 (32.76)EXPB6 (42.4)EXPB3 (205.69)EXPB4 (518.98)
XTH12 (7.76)XTH28 (11.53)XTH19 (29.16)XTH2 (31.35)XTH24 (36.15)XTH21 (37.16)XTH1 (45.29)XTH27 (64.75)XTH17 (101.83)XTH3 (140.51)XTH23 (162.11)XTH11 (226.32)XTH10 (460.38)
PME3 (21.62)PME29 (24.53)PME7 (83.85)
FLA4 (20.24)FLA5 (26.73)FLA24 (36.75)FLA11 (41.68)FLA16 (41.91)FLA1 (48.26)FLA2 (51.13)FLA6 (73.41)FLA7 (102.53)FLA3 (130.15)
OS01G0594300 (16.42)OS04G0670100 (18.23)OS02G0138000 (18.46)OS01G0180000 (21.72)OS07G0176500 (24.16)OS05G0180300 (27.48)OS02G0616100 (37.23)OS04G0505200 (90.09)
-2 0 2 4
C9285A
B C
D E
1 cm
newlyelongated internode
non-elongated internode
2nd node
3rd node
basal nodebasal node
2nd node
3rd node1
cm
DW 0 d DW 2 d
Tota
l lig
nin
cont
ent
(% d
ry w
eigh
t)
012345678
basalnode
2nd+3rdnode
non-elongatedinternode
Tota
l lig
nin
cont
ent
(% d
ry w
eigh
t)
0
1
2
3
4
5
6
7
basalnode
2ndnode
non-elongatedinternode
3rdnode
newlyelongatedinternode
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 240
20
40
60
submergence time point (h)
expr
essi
on (c
pm)
CAD1
CAD2
CAD3
CAD4
CAD6
CAD7
CAD8A
CAD8B
CAD8C
CAD8D
CAD9
DW 0 d DW 2 d
log2 FCrelative to T65 0 h
0 1 3 6 12 24
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 24
submergence time point (h)
submergence time point (h)
C9285 6LS T65 6LSC9285
max cpm
α-expansinβ-expansin
XTH
PM
EA
GP
-likeextensin-like
0 1 3 6 12 24 0 1 3 6 12 24
EXPA6 (23.26)EXPLA3 (25.47)EXPLA2 (28.02)EXPA5 (29.65)EXPLA1 (41.01)EXPA3 (47.24)EXPA2 (66.36)EXPA4 (91)EXPA7 (95)
EXPB17 (17.14)EXPB16 (18.51)EXPB7 (20.68)EXPB12 (32.76)EXPB6 (42.4)EXPB3 (205.69)EXPB4 (518.98)
XTH12 (7.76)XTH28 (11.53)XTH19 (29.16)XTH2 (31.35)XTH24 (36.15)XTH21 (37.16)XTH1 (45.29)XTH27 (64.75)XTH17 (101.83)XTH3 (140.51)XTH23 (162.11)XTH11 (226.32)XTH10 (460.38)
PME3 (21.62)PME29 (24.53)PME7 (83.85)
FLA4 (20.24)FLA5 (26.73)FLA24 (36.75)FLA11 (41.68)FLA16 (41.91)FLA1 (48.26)FLA2 (51.13)FLA6 (73.41)FLA7 (102.53)FLA3 (130.15)
OS01G0594300 (16.42)OS04G0670100 (18.23)OS02G0138000 (18.46)OS01G0180000 (21.72)OS07G0176500 (24.16)OS05G0180300 (27.48)OS02G0616100 (37.23)OS04G0505200 (90.09)
-2 0 2 4
C9285A
B C
D E
1 cm
newlyelongated internode
non-elongated internode
2nd node
3rd node
basal nodebasal node
2nd node
3rd node
1 cm
DW 0 d DW 2 d
Tota
l lig
nin
cont
ent
(% d
ry w
eigh
t)
012345678
basalnode
2nd+3rdnode
non-elongatedinternode
Tota
l lig
nin
cont
ent
(% d
ry w
eigh
t)
0
1
2
3
4
5
6
7
basalnode
2ndnode
non-elongatedinternode
3rdnode
newlyelongatedinternode
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 240
20
40
60
submergence time point (h)
expr
essi
on (c
pm)
CAD1
CAD2
CAD3
CAD4
CAD6
CAD7
CAD8A
CAD8B
CAD8C
CAD8D
CAD9
DW 0 d DW 2 d
log2 FCrelative to T65 0 h
0 1 3 6 12 24
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 24submergence time point (h)
submergence time point (h)
C9285 6LS T65 6LSC9285
max cpm
α-expansinβ-expansin
XTH
PM
EA
GP
-likeextensin-like
0 1 3 6 12 24 0 1 3 6 12 24
EXPA6 (23.26)EXPLA3 (25.47)EXPLA2 (28.02)EXPA5 (29.65)EXPLA1 (41.01)EXPA3 (47.24)EXPA2 (66.36)EXPA4 (91)EXPA7 (95)
EXPB17 (17.14)EXPB16 (18.51)EXPB7 (20.68)EXPB12 (32.76)EXPB6 (42.4)EXPB3 (205.69)EXPB4 (518.98)
XTH12 (7.76)XTH28 (11.53)XTH19 (29.16)XTH2 (31.35)XTH24 (36.15)XTH21 (37.16)XTH1 (45.29)XTH27 (64.75)XTH17 (101.83)XTH3 (140.51)XTH23 (162.11)XTH11 (226.32)XTH10 (460.38)
PME3 (21.62)PME29 (24.53)PME7 (83.85)
FLA4 (20.24)FLA5 (26.73)FLA24 (36.75)FLA11 (41.68)FLA16 (41.91)FLA1 (48.26)FLA2 (51.13)FLA6 (73.41)FLA7 (102.53)FLA3 (130.15)
OS01G0594300 (16.42)OS04G0670100 (18.23)OS02G0138000 (18.46)OS01G0180000 (21.72)OS07G0176500 (24.16)OS05G0180300 (27.48)OS02G0616100 (37.23)OS04G0505200 (90.09)
-2 0 2 4
C9285A
B C
D E1
cm
newlyelongated internode
non-elongated internode
2nd node
3rd node
basal nodebasal node
2nd node
3rd node
1 cm
DW 0 d DW 2 d
Tota
l lig
nin
cont
ent
(% d
ry w
eigh
t)
012345678
basalnode
2nd+3rdnode
non-elongatedinternode
Tota
l lig
nin
cont
ent
(% d
ry w
eigh
t)
0
1
2
3
4
5
6
7
basalnode
2ndnode
non-elongatedinternode
3rdnode
newlyelongatedinternode
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 240
20
40
60
submergence time point (h)
expr
essi
on (c
pm)
CAD1
CAD2
CAD3
CAD4
CAD6
CAD7
CAD8A
CAD8B
CAD8C
CAD8D
CAD9
DW 0 d DW 2 d
log2 FCrelative to T65 0 h
0 1 3 6 12 24
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 24
XTH
β-ex
pans
inα-
expa
nsin
fasc
iclin
-like
AG
Pex
tens
in-li
ke
submergence time point (h)
submergence time point (h)
C9285 6LS T65 6LSC9285
max cpm
α-expansinβ-expansin
XTH
PM
EA
GP
-likeextensin-like
0 1 3 6 12 24 0 1 3 6 12 24
EXPA6 (23.26)EXPLA3 (25.47)EXPLA2 (28.02)EXPA5 (29.65)EXPLA1 (41.01)EXPA3 (47.24)EXPA2 (66.36)EXPA4 (91)EXPA7 (95)
EXPB17 (17.14)EXPB16 (18.51)EXPB7 (20.68)EXPB12 (32.76)EXPB6 (42.4)EXPB3 (205.69)EXPB4 (518.98)
XTH12 (7.76)XTH28 (11.53)XTH19 (29.16)XTH2 (31.35)XTH24 (36.15)XTH21 (37.16)XTH1 (45.29)XTH27 (64.75)XTH17 (101.83)XTH3 (140.51)XTH23 (162.11)XTH11 (226.32)XTH10 (460.38)
PME3 (21.62)PME29 (24.53)PME7 (83.85)
FLA4 (20.24)FLA5 (26.73)FLA24 (36.75)FLA11 (41.68)FLA16 (41.91)FLA1 (48.26)FLA2 (51.13)FLA6 (73.41)FLA7 (102.53)FLA3 (130.15)
OS01G0594300 (16.42)OS04G0670100 (18.23)OS02G0138000 (18.46)OS01G0180000 (21.72)OS07G0176500 (24.16)OS05G0180300 (27.48)OS02G0616100 (37.23)OS04G0505200 (90.09)
-2 0 2 4
C9285A
B C
D E
1 cm
newlyelongated internode
non-elongated internode
2nd node
3rd node
basal nodebasal node
2nd node
3rd node
1 cm
DW 0 d DW 2 d
Tota
l lig
nin
cont
ent
(% d
ry w
eigh
t)
012345678
basalnode
2nd+3rdnode
non-elongatedinternode
Tota
l lig
nin
cont
ent
(% d
ry w
eigh
t)
0
1
2
3
4
5
6
7
basalnode
2ndnode
non-elongatedinternode
3rdnode
newlyelongatedinternode
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 240
20
40
60
submergence time point (h)
expr
essi
on (c
pm)
CAD1
CAD2
CAD3
CAD4
CAD6
CAD7
CAD8A
CAD8B
CAD8C
CAD8D
CAD9
DW 0 d DW 2 d
log2 FCrelative to T65 0 h
0 1 3 6 12 24
C9285 6LS T65 6LS
0 1 3 6 12 24 0 1 3 6 12 24
PM
E
a a aa
aa
bb
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Figure 8. Submergence-induced transcripts from C9285-unique loci.Expression from selected loci which are presumably absent in the IRGSP1.0 reference genome is shown. Each row represents one locus, columns represent samples from different time points after submergence and colors represent gene expression levels as log2 transformed counts per million values (cpm) normalized to the average expression in all samples of different time points. Genes that have an at least two-fold increase in expression after submergence in C9285 6 LS plants are shown. Complete expression data from C9285-unique transcripts can be found in Supplemental Dataset 10 and sequence data is provided in Supplemental Datasets 12 to 14.
contig_31:434-1084contig_22:1359-2511contig_23:2082-5157contig_14:1058-2399contig_12:7770-10275contig_3:7545-12614contig_7:4617-9033contig_22:2607-4832contig_13:2616-6249contig_24:803-5067contig_8:9243-11357contig_20:2230-5386contig_28:769-3481contig_2:4464-6707contig_17:810-6158contig_21:785-1970contig_29:1648-2639
0 1 3 6 12 24submergence time point (h)
-2 -1 0 1
average log2 FC
relative to row mean
con�glength pep�delength(bp) (AA)2921 272 OsI_30077NB-ARCdomainprotein5576 257 SK1ethyleneresponsefactor6299 974 XP_006663590RPM1-likediseaseresistanceprotein16325 681 OsJ_13717DUFprotein3549 306 XP_004952393thauma�n-likeprotein1b5788 378 XP_006660338RGA4-likediseaseresistanceprotein12025 259 SK2ethyleneresponsefactor5091 104 OSJNBa0019J05.12RT-LTRrelatedprotein9804 611 OsI_14912puta�veSAM-dependentmethyltransferase5753 512 EMT18893DiseaseresistanceproteinRPM12074 1042 XP_006657081LRRreceptorkinase,EFR-like15513 810 NBS-LRRtypeprotein10276 835 puta�veRNAhelicase9621 140 puta�veTy1-copiaretrotransposonprotein5223 239 Cysteine-richreceptor-likeproteinkinase85753 147 DiseaseresistanceproteinRPM12453 172 OsI_30538,hypothe�calprotein
descrip�on
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