Improving crop models in the face of

climate change (Viewpoint)

doi:10.1093/aob/mct016 and 10.1093/aob/mct130

Crop models need improving for an accurate assessment ofthe impacts of climate change on crop productivity. Yin(pp. 465–475) considers that most existing models are unableto accommodate photosynthetic acclimation to CO2

concentrations, and therefore tend to overpredict crop responsesto elevated CO2. Strong evidence is provided for the need toquantify carbon–nitrogen interactions in order to simulate thisacclimation mechanism. This would provide a basis for amechanistic framework that models critical physiologicalprocesses and traits in response to other climatic factors andextreme weather events. In an accompanying article, Kimball(pp. 477–478) comments on a methodological error in apreviously published report of a free-air CO2 enrichment(FACE) study that is cited by Yin.

Plant biodiversity conservation in

montane ecosystems (Invited

Review)

doi:10.1093/aob/mct125

Mountain ecosystems are hot spots for plant conservationefforts because they have high plant diversity as communitiesreplace each other along altitudinal and climatic gradients, andthey have a high proportion of endemic species. Khan et al.(pp. 479–501) review the need to integrate differentconservation criteria and methodologies and suggest newmeans of assessing anthropogenic pressure on plantbiodiversity at both species and community levels. Theyconsider plant diversity in mountain ecosystems with specialreference to the western Himalayas, ethnobotanical andecosystem service values of mountain vegetation within thecontext of anthropogenic impacts, and local and regional plantconservation strategies and priorities.

Pectin and AGP mapping in

germinating olive pollen

doi:10.1093/aob/mct118

Cell wall pectins and arabinogalactan proteins (AGPs) areimportant for pollen tube growth. Castro et al. (pp. 503–513)study AGPs in olive (Olea europaea) pollen and find that theyare newly synthesized during germination, with production andsecretion being spatially and temporally regulated. Theysuggest that galactans may provide mechanical stability to thepollen tube, reinforcing those regions that are sensitive totension stress and mechanical damage, and arabinans and AGPsmay be important in recognition and adhesion properties of thepollen tube and the stylar transmitting cells, as well as the eggand sperm cells.

Species coherence in a

cytogenetically diverse sedge

doi:10.1093/aob/mct119

The sedge genus Carex, the most diversified angiosperm genusof the northern temperate zone, is known for its holocentricchromosomes and karyotype variability. Escudero et al.(pp. 515–526) provide the first comprehensive study ofpopulation-level patterns of molecular and cytogeneticdifferentiation in the genus. They demonstrate dispersal andgenetic connectivity among populations of the North AmericanCarex scoparia that differ in chromosome numbers, demonstratingthat cytogenetically variable sedge species can still coheregenetically. This finding is important to our understanding of whatconstitutes a species in one of the world’s largest angiospermgenera.

Highly conserved B chromosomes in

rye

doi:10.1093/aob/mct121

Supernumerary B chromosomes (Bs) represent a specific type of‘selfish’ genetic element. As they are dispensable for normalgrowth, they generally show polymorphisms among populations.Marques et al. (pp. 527–534) analyse the distribution andactivity of B-located repeats in cultivated rye, Secale cerealesubsp. cereale, and weedy relatives from seven countries rangingfrom Turkey to Japan and find that Bs maintain a similarmolecular structure at the subspecies level. The high degree ofconservation of the non-disjunction control region underlines itsfunctional importance for the maintenance of B chromosomes.The conserved structure suggests that although rye Bsexperienced rapid evolution including multiple rearrangements atthe early evolutionary stages, this process has slowedsignificantly and may have even ceased during its recentevolution.

Gymnosperm B-sister genes and

ovule/seed development

doi:10.1093/aob/mct124

Seeds are produced by gymnosperms and angiosperms but only thelatter have an ovary to be transformed into a fruit. Lovsisetto et al.(pp. 535–544) study B-sister genes from two gymnosperms,Ginkgo biloba and Taxus baccata, and find that in Ginkgo the geneis involved in the growth of ovular-derived fleshy fruit. Theyfunctionally characterize the gene by ectopically expressing it intobacco. In contrast, the fleshy structure in Taxus derives from anoutgrowth of the ovule peduncle, and the B-sister gene is notinvolved in its growth. They suggest that B-sister genes have aprimary function in ovule/seed development and a subsidiary rolein the formation of fleshy fruit-like structures when the latter havean ovular origin, as observed in Ginkgo.

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Repetitive component of the peanut

A genome

doi:10.1093/aob/mct128

Peanut (Arachis hypogaea) is an allotetraploid (AABB-typegenome) of recent origin. Bertioli et al. (pp. 545–559) study theevolution of the A genome, focusing on its highly repetitivecomponent. They find that a substantial proportion of the repetitivecontent appears to be accounted for by relatively few longterminal repeat (LTR) retrotransposons and their truncated copiesor solo LTRs, mostly non-autonomous. The retrotransposonsdescribed are all transcribed, although levels are low. Theyconclude that the activity of these retrotransposons has been a verysignificant driver of genome evolution since the divergence of thepeanut A and B genomes.

Individual mating patterns in mixed

oak stands

doi:10.1093/aob/mct131

Individual variation in mating patterns may have significantimplications for persistence and adaptation of plant populations,but field data generally focus on population averages. Using aBayesian approach, Chybicki and Burczyk (pp. 561–574)examine the extent of individual variation of several componentsof mating patterns in a mixed stand of Quercus robur andQ. petraea. They find that there is a great variation in intra- andinter-specific individual mating preferences, individual pollenimmigration rates and heterogeneity of immigrating pollen. Theyshow that trees can mate assortatively, with little respect to spatialproximity. Such selective mating may be a result of variablecompatibility among trees due to genetic and/or environmentalfactors.

Carbohydrate storage and

allometric partitioning in juvenile

trees

doi:10.1093/aob/mct132

Biomass partitioning for resource conservation might affect plantallometry, accounting for a substantial amount of unexplainedvariation in existing plant allometry models. Tomlinson et al. (pp.575–587) compare root carbohydrate storage and organ biomassallometries for juveniles of 20 savanna tree species of different leafhabit – nine evergreen and 11 deciduous – and find that deciduousspecies have greater root non-structural carbohydrate thanevergreens, and lower scaling exponents for leaf-to-root andstem-to-root partitioning. The data provide strong support for thehypothesis that deciduous and evergreen trees differ in juvenilebiomass allometries because of differences in allocation to rootstorage. Substantial unexplained variation in biomass allometry ofwoody species may be related to selection for resourceconservation against environmental stresses, such as resourceseasonality.

Molecular analyses help resolve the

evolution of Platanus

doi:10.1093/aob/mct134

Recent research on the history of Platanus has shown that complexhybridization phenomena occurred in the central Americanspecies, and its evolutionary history remains unresolved. DeCastro et al. (pp. 589–602) employ sequencing of a uniparentalcpDNA marker ( psbA-trnH(GUG) intergenic spacer) andqualitative and quantitative SNP genotyping of biparental nrDNAmarkers (LFY-i2 and ITS2) to confirm that hybridization andintrogression events between lineages ancestral to modern centraland eastern North American Platanus species occurred.Chloroplast haplotypes and qualitative and quantitative SNPgenotyping provide information critical for understanding thecomplex history of Mexican Platanus. Compared with the usualmolecular techniques of sub-cloning, sequencing and genotyping,the real-time PCR assay employed provides a quick and sensitivetechnique for analysing complex evolutionary patterns.

HvAACT1 increases Al31-tolerance

in wheat and barley

doi:10.1093/aob/mct135

Al3+-activated release of citrate from the root apices ofaluminium-tolerant genotypes of barley is controlled by a MATEgene named HvAACT1 that encodes a citrate transporter. Zhouet al. (pp. 603–612) over-express HvAACT1 in wheat (Triticumaestivum) and barley (Hordeum vulgare) using the maize ubiquitinpromoter, and find that increased expression in both species isassociated with increased citrate efflux from root apices, and thatthis enhances Al3+ tolerance in both hydroponic solution and inacid soil. Genetically modifying barley and wheat to express thebarley gene HvAACT1 gene therefore has potential in helping toalleviate the effects of aluminium toxicity in acid soils.

Maternal sex effects and inbreeding

depression in Fragaria

doi:10.1093/aob/mct120

Gynodioecy (coexistence of females and hermaphrodites) is asexual system that occurs in numerous flowering plant lineages. Inorder to understand the maintenance of gynodioecy, Dalton et al.(pp. 613–621) examine the effect of maternal sex type andinbreeding depression (IBD) on plant performance across severalresource conditions and life stages in woodland strawberry,Fragaria vesca subsp. bracteata. They find that maternal genotypeand resources influence the magnitude of both maternal sex effectsand IBD, with progeny of females being more likely to germinateunder benign conditions and survive under stress. Cumulative IBDis low but increases with life stage. Assuming the results arerepresentative for this long-lived perennial, then neither femalematernal advantage nor IBD are strong enough to maintaingynodioecy under nuclear models of sex inheritance.

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Carbon budgets in deciduous and

evergreen treeline species

doi:10.1093/aob/mct127

The growth limitation hypothesis proposes that treelines formbecause carbonsinksare more restrictedby low temperaturesthanbycarbon sources, but most supporting evidence comes fromevergreenspecies. Fajardo et al. (pp. 623–631) examine tree growth andconcentrations of non-structural carbohydrates (NSCs) at fourelevations in six deciduous–evergreen mixed-species forests in thesouthern Andes and the Swiss Alps, and find that both foliartypes are sink-limited when faced with decreasing temperatures.Despite the deciduous tree species having significantly higher NSCsthan evergreens, no indication is found of carbon limitation indeciduous species in the alpine treeline ecotone.

miRNAs responsive to low nitrate

doi:10.1093/aob/mct133

MicroRNAs (miRNAs) play an important role in adaptation ofplants to many stresses including low nitrogen availability.Zhao et al. (pp. 633–642) identify miRNAs and their targetsin maize (Zea mays) subjected to low-nitrogen stress bycombined analysis of deep sequencing of small RNA anddegradome libraries. Of 85 potentially new miRNAs, 25 show amore than two-fold relative change in response to low-nitrogencompared to optimal conditions, and two novel putativemiR169 species are identified. The results will help increaseunderstanding of the physiological basis for low-nitrogentolerance and adaptation in maize.

Plant Cuttings Annals of Botany 112: iii–v, 2013

Available online at www.aob.oxfordjournals.org

News in Botany: Nigel Chaffey presents a round-up of plant-based items from the world’s media

Plant Cuttings has changed . . .

We’re experimenting with a newformat for the Plant Cuttings thismonth. Whilst applauding theeclectic mix of content each issue,some readers of this column haveexpressed concern that inclusion ofthe full citationswithin the text spoilstheir enjoyment of the news itemsbecause this hinders the narrativeflow. So, balancing the need to

provide evidence-based science communication and readability,for this issue, in-text references are replaced with numbers, andfullercitation(s)appear below the news item.What do you think?Is this better? Do let me know – either on Twitter: @NChaffey,or via e-mail: n.chaffey@bathspa.ac.uk. Thank you.

Image: Wikimedia Commons.

Brachypodium is NOT Arabidopsis(!)

Yes, arabidopsis is a modelorganism[1–3], but for what exactly?Many would like us to believe that itis a model for all things botanical,i.e. plants. However, with thoseorganisms newly defined as‘photosynthetic eukaryoticorganisms, including algae andpossibly cyanobacteria’[4], that is atruly tall order for such a slightspecimen! And arguably an extremepoint of view (although entirelyunderstandable if one’s past, present

and future employment is tied to research grants using thisbeast). And, at the other end of the spectrum, there are thosewho espouse the view that arabidopsis is truly only a model forother arabidopses. Well, adding to the debate, David

Pacheco-Villalobos et al. reveal that interactions between theplant hormones[5,6] ethylene and auxin in roots of themonocot Brachypodium distachyon (‘another’ modelplant[7,8]) differ to those in roots of the dicot Arabidopsis[9].Wheras lowered levels of auxin in Arabidopsis, which can becaused by increases in another hormone – ethylene – result inshorter roots, in Brachypodium increases in ethylene lead toelevated levels of auxin and longer roots(!). The latter’s‘inverted regulatory relation between the two hormones’ pointsto ‘a complex homeostatic crosstalk between auxin andethylene in Brachypodium roots, which is fundamentallydifferent from Arabidopsis and might be conserved in othermonocotyledons’. So, and as those scientists sagely state,‘Observations gained from model organisms are essential, yet itremains unclear to which degree they are applicable to distantrelatives’. And, further complicating the ethylene story – ifsuch was needed at this stage – ‘Scientists identify thousands ofplant genes activated by ethylene gas’[10]. Examiningtranscriptional response to ethylene, Katherine Chang et al.have shown that this gaseous plant hormone is involved in anextensive network of cross-regulation with many other planthormones centred around EIN3, a transcription factor thatacts as the ‘master regulator’ of the ethylene signallingpathway[11]. Although this work was performed in arabidopsis,EIN3 orthologs[12,13] exist in many other plants, so thisstudy is anticipated to have broader relevance to . . . poplar,soybean, rice, maize, moss and multicellular algae.

Image: Neil Harris, University of Alberta/Wikimedia Commons.

[1] http://bit.ly/12QsSbE; [2] http://bit.ly/182JpPt; [3] http://bit.ly/10IwGzf;[4] http://aobblog.com/2013/07/seb2013-science-with-impact/;[5] http://en.wikipedia.org/wiki/Plant_hormone;[6] http://www.plant-hormones.info/Index.htm; [7] John Draper et al.,

Plant Physiology 127: 1539–1555, 2001; [8] http://1.usa.gov/12lOxIW;[9] Pacheco-Villalobos et al., PloS Genetics 9: e1003564, 2013;[10] http://bit.ly/14CJRT9; [11] Chang et al., eLIFE, 2: e00675, 2013;[12] http://bit.ly/13w5U0W; [13] http://bit.ly/12lPhh2.

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