Strigolactones: a new hormone with a past
-
Upload
yuichiro-tsuchiya -
Category
Documents
-
view
212 -
download
0
Transcript of Strigolactones: a new hormone with a past
Available online at www.sciencedirect.com
Strigolactones: a new hormone with a pastYuichiro Tsuchiya and Peter McCourt
The recent discovery of an endogenous hormonal activity for
strigolactones in shoot branching was surprising since these
molecules were thought to mostly play roles as signaling
molecules between organisms. Even in the context of plant
hormones, strigolactones appear to be different in that their
role in plant development is quite restricted. This most probably
reflects early days and new hormonal functions will most
probably be found for these compounds in the future. In this
respect, the exogenous role of strigolactones in parasitic plant
seed germination may hint to functions of this compound in
seed development. However, showing new roles for
strigolactones in the seed or any other aspect of plant
development for that matter will require developing assays in
model genetic systems such as Arabidopsis and rice where we
can take full advantage of the experimental tools that are
available.
Address
Department of Cell & Systems Biology, University of Toronto, 25
Willcocks Street, Toronto ON M5S 3B2, Canada
Corresponding author: McCourt, Peter ([email protected])
Current Opinion in Plant Biology 2009, 12:556–561
This review comes from a themed issue on
Cell signalling and gene regulation
Edited by Jan U. Lohmann and Jennifer L. Nemhauser
Available online 31st August 2009
1369-5266/$ – see front matter
# 2009 Elsevier Ltd. All rights reserved.
DOI 10.1016/j.pbi.2009.07.018
IntroductionUsually plant biologists are interested in five plant hor-
mones – auxins, cytokinins, ethylene, gibberellins and
abscisic acid – which is enough since this gang of five
seems to be involved in modulating everything. To make
matters worse, the list of hormones appears to be growing
with new molecules such as bassinosteroids and jasmo-
nates been added to the list. To keep this list manageable,
developmental biologists have come up with some simple
rules of what is a hormone. First, a compound of interest
must be made in small quantities and work at nanomolar
to micromolar ranges. Second, mutants defective in the
synthesis of an interesting molecule must have specific
developmental defects before it can be classified as a
hormone. These rules have meant most developmental
biologists did not have to worry about the myriad of
secondary products produced by plants. With this said,
Current Opinion in Plant Biology 2009, 12:556–561
the recent discovery that a collection of organically
related compounds, generically called strigolactones,
are also hormones was still surprising. Strigolactones have
long been of interest because they act as germination
stimulants for seeds of parasitic weeds of the genera Strigaand Orobanche and this parasitism is the scourge of agri-
culture in the developing world [1,2��,3]. In Africa alone
Striga species have infested up to two-thirds of the arable
land and are thought to cause 10 of billions of dollars in
lost crop yields. Striga species parasitize mostly tropical
monocotyledonous cereal crops whereas Orobanchespecies are limited to dicotyledonous crops found in
semi-temperate regions.
Although separated geographically and by host range, the
lifecycles of both Striga and Orobanche ssp. are similar.
Their seeds remain dormant in the soil until they sense
the growing roots of a potential host (Figure 1). Following
this event, the seeds germinate and grow toward a host
until their roots attach. After the successful establishment
of root vascular connections, the parasitic plant begins to
withdraw both nutrients and water resulting in dramatic
decreases in crop growth. Parasitic plant seeds are rela-
tively small and contain little nutrient reserve. Hence, the
germinating seeds must find a host root within a few days
of germination or it will die. Parasitic seeds will only
germinate when they are within 20 mm of a host root
(Figure 1). This small activation zone between a parasitic
seed and its host root suggested the host was producing a
germination stimulant. Subsequent analysis of root exu-
dates that could induce parasitic seed germination led to
the identification strigolactones [4��]. The basic structural
unit of a strigolactone is a tricyclic lactone that is con-
nected to a butyrolactone by an enol ester bridge
(Figure 2). On the basis of this core structure and on
the reduced efficiency at which various maize carotenoid
biosynthetic mutants could stimulate Striga germination
had led to the suggestion that strigolactones are derived
from a carotenoid-based pathway that has shared steps
with the hormone abscisic acid (ABA) [5].
However, it is clear that host plants do not make strigo-
lactones for the benefit of the parasite. This was further
supported by the fact that the first identified strigolactone
was purified from cotton plants, which are not normally
infected by Striga species [6]. The ability of non-host
plants to germinate parasitic plant seeds suggested stri-
golactones may exist ubiquitously in higher plants and
may have role(s) that are independent of host–parasite
interactions. Evidence for new roles of strigolactones
came from an unusual source when it was discovered
that the strigolactone, 5-deoxy-strigol, was required as a
www.sciencedirect.com
Strigolactones: a new hormone with a past Tsuchiya and McCourt 557
Figure 1
Strigolactones influence the germination of parasitic seeds and branching patterns of mycorryzial fungi. On the left a host plant exudes strigolactone
into the soil, which activates dormant parasitic plant seed to germinate. If the seed radicle reaches the host root it will establish a parasitic interaction.
On the right a host plant exudes strigolactone into the soil, which is sensed by the hyphe of an arbuscular mycorrhizal fungus. In responding to
strigolactone the hyphal growth is directed toward the plant root. Once an interaction is established the two organisms mutually exchange sugar from
the plant and nitrogen from the fungi.
branching factor to help arbuscular mycorrhizal fungi to
interact with plant roots (Figure 1) [7]. Mycorrhizal fungi
cannot develop in the absence of their plant partner
because the plant supplies carbon in the form of glucose
to the fungi. In return, the fungus improves the transfer of
nutrients to the plant root that is used for the synthesis of
amino acids [8]. This mutualistic relationship does
explain why some plants not involved in plant parasitic
interaction may exude strigolactones. However, this sym-
biotic communication could not be the whole story.
Although eighty percent of land plants form a mycorrhizal
interaction, many plants that produce strigolactones, do
not require any fungal partners for good growth [9,10�].
Branching out is hard to doThe absence of a natural plant parasite or a mycorrhizal
interaction for some plants suggested strigolactones have
other functions. But what were these role(s)? An insight
came with the finding that a collection of shoot branching
defective mutants in a variety of species were phenoty-
pically rescued by strigolactone addition [11��,12��]. This
story began with a collection of loss-of-function mutants
of pea, petunia, rice, and Arabidopsis that were originally
identified by their enhanced shoot branching [13].
Because of its sophisticated molecular genetics Arabidop-
sis researchers were able to show that two of these genes,
MAX3 and MAX4, encoded carotene-deoxygenases
(CCDs) that were most probably involved in carotene
degradation (Figure 2) [14,15]. Subsequent studies
showed that some of the branching defective mutants
in the other species were also defective in these CCD
genes [15]. Although the products of the MAX3 and
www.sciencedirect.com
MAX4 CCDs in planta are sketchy, some knowledge of
their potential cleavage products has been predicted from
expression of these genes in E. coli [16]. This finding
paired with the belief that strigolactones were carotenoid
derivatives was bought together when analytical analysis
demonstrated that various branching mutants in pea and
rice showed reduced levels of strigolactones [11��,12��].Finally, a synthetic strigolactone analogue, GR24, was
able to phenotypically rescue a variety of branching
mutants in different species including Arabidopsis clearly
showed strigolactones were necessary for normal plant
shoot development.
The carotenoid-based origins of strigolactones and ABA
have interesting biosynthesis and developmental implica-
tions since ABA is a germination inhibitor whereas stri-
golactones appear to stimulate germination at least in
parasitic plants. Actually of the nine CCDs that exist in
the Arabidopsis genome five are involved in ABA syn-
thesis. This raises questions about the interactions be-
tween these two biosynthetic pathways and the role of
ABA itself on strigolactone production. We know that null
mutations in CCDs involved in ABA synthesis in tomato
or maize do reduce the ability of these plants to germinate
parasitic seeds and this has been correlated with a
reduction in strigolactone levels [17]. This could mean
a CCD involved in ABA synthesis is also involved in
strigolactone biosynthesis. Alternatively, the reduced stri-
golactone levels may indirectly reflect a regulatory role of
ABA on the synthesis of this hormone. These possibilities
could be resolved by measuring strigolactone levels in
ABA biosynthesis mutants versus signaling mutants.
Current Opinion in Plant Biology 2009, 12:556–561
558 Cell signalling and gene regulation
Figure 2
A partially predicted pathway of strigolactone biosynthesis based on branching biosynthetic mutants from a variety of plant species. The products of
CC7 and CCD8 enzymes are based on heterologous enzymatic analysis in E. coli. The gene names on the right are based on mutants identified from
various plant species. The D27 mutant has only been identified in rice and the P450/MAX1 mutant has only been identified in Arabidopsis. At the
bottom are structures of a small number of natural and synthetic strigolactones. Strigol stimulates Striga germination whereas Orobanchol stimulates
Orobanche species seed germination. Strigol and 5-deoxystrigol have been identified in monocotyledonous plants and Orobanchol is usually found in
dicotyledonous species.
A third gene, MAX1, which encodes a Cytochrome P450,
also appears to be involved in strigolactone synthesis at
least in Arabidopsis [18]. At this stage it is difficult to
know where MAX1 fits into the biosynthetic pathway but
it is assumed this cytochrome acts downstream of the two
CCDs [11��,12��]. Interestingly, the equivalent loss-of-
function max1 mutations have not been identified in any
other plant species, which may mean the ‘MAX pathway’
in Arabidopsis, is not completely conserved across plant
species. Perhaps this just reflects genetic redundancy
issues between species or maybe there is a more provo-
cative reason that reflects selective differences between
non-mycorrhizal species such as Arabidopsis with species
that have evolved a mycorrhizal symbiosis. Finally, a new
gene involved in strigolactone biosynthesis has recently
been identified in rice [19�]. Originally identified as the
recessive dwarf27 (d27) mutation that conferred an
increased branching phenotype, this mutant was later
shown to have low strigolactone levels and its mutant
phenotypes could be rescued by strigolactone addition.
Current Opinion in Plant Biology 2009, 12:556–561
Molecular characterization of the D27 gene shows it
encodes a novel iron containing protein [19�]. The role
of this gene in strigolactone synthesis is unclear and this
finding does demonstrate how much we still have to learn
about the strigolactone biosynthesis.
Although it is now obvious that strigolactones are
involved in shoot branching, how does this molecule
contribute to this developmental response? This will of
course require the identification of its receptor and the
genes that it regulates. However, we do know that part of
the answer involves how strigolactones interact with other
hormones and in particular auxin and cytokinin. Auxin is
actively transported downward from the top of a plant and
this action inhibits axillary bud outgrowth and hence
branching [20�]. Conversely, cytokinin is transported
upwards from the root to activate bud outgrowth. In
strigolactone deficient mutants there is a higher transport
capacity in the stem owing to upregulation of auxin
transporters [21]. These observations have led to a clever
www.sciencedirect.com
Strigolactones: a new hormone with a past Tsuchiya and McCourt 559
model that is akin to traffic congestion. In wild-type
plants, strigolactones or a downstream product, acts like
a flashing orange light slowing the flow of auxin down the
main artery of the stem. As a consequence, auxin made in
axillary buds, which would be analogous to cars trying to
enter onto the main road cannot go in and this backlog
leads to increased auxin levels in the bud, which inhibits
outgrowth. However, recent reports also suggest strigo-
lactones act downstream of auxins and are dependent on
auxin for their synthesis [22�]. Undoubtedly these nuan-
ces will be resolved but these conflicting results still show
that strigolactones, like all plant hormones, have complex
relationships with other hormones. With this said, it is
surprising that strigolactone deficient mutants have phe-
notypes that are limited to shoot branching and a slightly
reduced stature. This is in contrast to most hormone
mutants, which often show a dizzying array of pheno-
types. Perhaps this apparent developmental specificity
will fall away when more detailed phenotypic analysis is
done on these branching mutants.
More mutants, more phenotypingThe lack of more strigolactone-dependent phenotypes on
the basis of genetic analysis does appear to set this
hormone apart from others traditional plant hormones.
This has led to suggestions that strigolactones may
represent more specialized signaling molecules [11��].Some hints that this may not be the case comes from
mutations that appear to influence strigolactone signaling.
Loss-of-function mutations in the MAX2 gene have the
same branching defects of strigolactone deficient
mutants. However, unlike the biosynthetic mutants,
the increased branching in a max2 plant is not rescued
by exogenous strigolactone [23]. Molecular identification
of the MAX2 gene showed it encoded an F-box protein
indicating protein turnover is most probably an integral
part of strigolactone signal transduction [23]. Interest-
ingly, F-box proteins have turned out to be key regulators
of a number of hormone signaling pathways that target
specific transcription factors [24]. What is interesting
about max2 mutants is that they have added phenotypes
beyond increased branching such as altered light respon-
siveness and senescence [25,26]. A simple explanation is
the biosynthetic mutants are leaky, which may be true
since CCD mutants still showed strigolactone activity in
parasitic plant seed germination assays [11��,12��]. This
remaining activity may reflect the genetic redundancy of
the CCD gene family or may mean strigolactones have
alternative biosynthetic pathways [27]. It is also possible
that unlike strigolactone biosynthesis mutants the MAX2
F-box is used in strigolactone-independent processes.
This would be unusual since the F-box proteins involved
in other hormone signaling pathways appear to be specific
to that particular hormone [24].
To clearly define the roles of strigolactones in plant growth
and development will first require more strigolactone
www.sciencedirect.com
mutants and second, better developmental and molecular
phenotyping. In these respects rice may actually lead the
way. Defects in shoot branching can be easily identified at
early stages of rice growth and this has led to the identi-
fication of many varieties with altered branching patterns.
For example, the DWARF14 (D14) mutant of rice looks like
a strigolactone deficient mutant, however, it is not rescued
by strigolactone addition [28��]. Positional cloning of the
D14 locus shows it encodes a protein related to a hydrolase
superfamily that has previously included proteins with
roles in hormone metabolism and signaling. Intriguingly,
the rice GA receptor GID1 is a member of this family. This
molecular relatedness, coupled with the role of F-box
proteins in strigolactone signaling, could mean many of
the core components of strigolactone signaling may be
similar to those found in GA signaling.
With respect to finding new phenotypes, perhaps seed
development is first place to start. Because strigolactones
are important regulators in parasitic plant germination is it
possible that this hormone has a general developmental
role in this process? Early work on lettuce and wild oats
seed germination did suggest strigolactones have a
positive influence on germination [29,30]. Thus, the
response of parasitic plants to strigolactones may reflect
an evolved response that sensitizes germination responses
of these plants to strigolactones. A widespread role for
strigolactones in seed germination, however, is not sup-
ported by the observation that strigolactone mutants do
not show obvious seed germination defects. Although the
genetics argues against a general role for strigolactones in
germination it is also possible that the model plants in
which strigolactone mutants have been identified are
themselves biased. For example, the commonly used
Arabidopsis laboratory accessions such as Col and Ler
have relatively weak seed dormancy under normal growth
and storage conditions. Therefore, these ecotypic back-
grounds may not be well suited for addressing relation-
ships between strigolactones and seed development [31].
Possibly strigolactone studies involving Arabidopsis
should be carried out using accessions such as Cvi, which
has deep seed dormancy compared with most laboratory
accessions. Weather strigolactones are specialized or have
broader roles in plant development will have to be seen
but certainly they have joined the ‘plant hormone club’.
However, although it is generally thought that plant
hormones are integrators of environmental inputs with
plant development, strigolactones have the added role of
also shaping the environmental signals themselves
through the organisms with which they interact. This
means the evolution of strigolactones may be different
than other endogenous plant hormones. Unlike ABA, for
example, which has a conserved structure across plant
species, a wide array of natural strigolactones has been
isolated. What this means about the evolutionary history
and current roles of this new hormone class remains to be
discovered.
Current Opinion in Plant Biology 2009, 12:556–561
560 Cell signalling and gene regulation
References and recommended readingPapers of particular interest, published within the period of review,have been highlighted as:
� of special interest
�� of outstanding interest
1. Joel DM, Hershenhom Y, Ejeta G, Rich JP: Biology andmanagement of weedy root parasites. Hort Rev 2007,33:267-349.
2.��
Lopez-Raez JA, Matusova R, Cardoso C, Jamil M, Charnikhova T,Kohlen W, Ruyter-Spira C, Verstappen F, Bouwmeester H:Strigolactones: ecological significance and use as a target forparasitic plant control. Pest Manag Sci 2009, 65:471-477.
This is an excellent up to date overview of parasitic plants in the context ofstrigolactones. It integrates much of the literature from both an ecologicaland molecular perspective. It also talks about how this work may beimplemented to control Striga infestations in the future.
3. Scholes JD, Press MC: Striga infestation of cereal crops—anunsolved problem in resource limited agriculture. Curr OpinPlant Biol 2008, 11:180-186.
4.��
Zwanenburg B, Mwakaboko AS, Reizelman A, Anilkumar G,Sethumadhavan D: Structure and function of natural andsynthetic signalling molecules in parasitic weed germination.Pest Manag Sci 2009, 65:478-491.
As a biologist, this review tells you more than you will ever need to knowabout the chemistry of strigolactones. However, this review demon-strates how understanding the chemistry of a molecule and its chemicalanalogues can be used at both a basic level to predicting the nature of thestrigolactone receptor. This review also demonstrates how powerfulchemical biology will be in the field of strigolactones and parasitic weeds.
5. Matusova R, Rani K, Verstappen FW, Franssen MC, Beale MH,Bouwmeester HJ: The strigolactone germination stimulants ofthe plant-parasitic Striga and Orobanche spp. are derivedfrom the carotenoid pathway. Plant Physiol 2005, 139:920-934.
6. Cook CE, Whichard LP, Turner B, Wall ME, Egley GH:Germination of witchweed (Striga lutea Lour.): isolation andproperties of a potent stimulant. Science 1966, 154:1189-1190.
7. Akiyama K, Matsuzaki K, Hayashi H: Plant sesquiterpenesinduce hyphal branching in arbuscular mycorrhizal fungi.Nature 2005, 435:824-827.
8. Govindarajulu M, Pfeffer PE, Jin H, Abubaker J, Douds DD,Allen JW, Bucking H, Lammers PJ, Shachar-Hill Y: Nitrogentransfer in the arbuscular mycorrhizal symbiosis. Nature 2005,435:819-823.
9. Goldwasser Y, Yoder JI: Differential induction of Orobancheseed germination by Arabidopsis thaliana. Plant Sci 2001,160:951-959.
10.�
Goldwasser Y, Yoneyama K, Xie X, Yoneyama K: Production ofstrigolactones in Arabidopsis thaliana responsible forOrobanche aegyptiaca seed germination. Plant Growth Reg2008, 55:21-28.
This study is the first to clearly show that Arabidopsis does makestrigolactone like molecules. It also shows that because of its small sizeand lack of characterized internal standards it is not yet possible to doquantitative analysis. For these reasons although max mutants in Arabi-dopsis have been instrumental in understanding the strigolactonebranching connection all analytical measurements have to be done inlarger species like pea [11��] and rice [12��]. This shows the advantage ofhaving related mutants in multiple species so as to take advantage ofeach ones attributes.
11.��
Gomez-Roldan V, Fermas S, Brewer PB, Puech-Pages V, Dun EA,Pillot JP, Letisse F, Matusova R, Danoun S, Portais JC et al.:Strigolactone inhibition of shoot branching. Nature 2008,455:189-194.
This study along with reference [12��] shows that a number of branchingmutants in were actually deficient in strigolatone. In this case, the authorsfocussed on pea. What is interesting is that although the structure ofstrigolactones has been known for forty years and it was predicted thesemutants were deficient in a carotenoid-based hormone it was onlyrecently that these two leads were put together. By contrast, theapproach to use metabolomics to find the signal does not appear tobe sensitive enough to find new growth regulators.
Current Opinion in Plant Biology 2009, 12:556–561
12.��
Umehara M, Hanada A, Yoshida S, Akiyama K, Arite T, Takeda-Kamiya N, Magome H, Kamiya Y, Shirasu K, Yoneyama K et al.:Inhibition of shoot branching by new terpenoid planthormones. Nature 2008, 455:195-200.
This study, like the previous one [11��], clearly showed that a number ofbranching mutants were actually deficient in strigolatone. These authorsfocussed on rice. Again this study linked the carotenoid pathway infor-mation to strigolactone structure by using mutants. It again shows howgenetics linked to good biochemistry can be so powerful in dissectinghormone synthesis and action.
13. McSteen P, Leyser O: Shoot branching. Annu Rev Plant Biol2005, 56:353-374.
14. Booker J, Auldridge M, Wills S, McCarty D, Klee H, Leyser O:MAX3/CCD7 is a carotenoid cleavage dioxygenase requiredfor the synthesis of a novel plant signaling molecule. Curr Biol2004, 14:1232-1238.
15. Sorefan K, Booker J, Haurogne K, Goussot M, Bainbridge K,Foo E, Chatfield S, Ward S, Beveridge C, Rameau C et al.: MAX4and RMS1 are orthologous dioxygenase-like genes thatregulate shoot branching in Arabidopsis and pea. Genes Dev2003, 17:1469-1474.
16. Alder A, Holdermann I, Beyer P, Al-Babili S: Carotenoidoxygenases involved in plant branching catalyse a highlyspecific conserved apocarotenoid cleavage reaction. BiochemJ 2008, 416:289-296.
17. Booker J, Sieberer T, Wright W, Williamson L, Willett B,Stirnberg P, Turnbull C, Srinivasan M, Goddard P, Leyser O:MAX1 encodes a cytochrome P450 family member that actsdownstream of MAX3/4 to produce a carotenoid-derivedbranch-inhibiting hormone. Dev Cell 2005, 8:443-449.
18. Lopez-Raez JA, Charnikhova T, Gomez-Roldan V, Matusova R,Kohlen W, De Vos R, Verstappen F, Puech-Pages V,Becard G, Mulder P et al.: Tomato strigolactones arederived from carotenoids and their biosynthesis ispromoted by phosphate starvation. New Phytol 2008,178:863-874.
19.�
Lin H, Wang R, Qian Q, Yan M, Meng X, Fu Z, Yan C, Jiang B, Su Z,Li J et al.: DWARF27, an iron-containing protein required for thebiosynthesis of strigolactones, regulates rice tiller budoutgrowth. Plant Cell 2009. [Epub ahead of print].
The discovery that the dwarf mutant d27 is defective in strigolactonesynthesis shows the advantage of using rice as a model system forstudying this hormone. This appears to be because defects in ricebranching can be identified quite early in development. With the wealthof dwarfed mutants that exist in rice it is possible rice will out competeother model systems such as Arabidopsis with regard to understandingstrigolactone synthesis and signaling at a molecular level.
20.�
Leyser O: The control of shoot branching: an example of plantinformation processing. Plant Cell Environ 2009 doi: 10.1111/1365-3040.2009.01930.x.
This is a very up to date review of axillary shoot branching both at adevelopmental and signaling perspective. The review also touches on therole of the environment in branching patterns with a very interestingsection on the light signaling and how it may play into various hormonepathways.
21. Bennett T, Sieberer T, Willett B, Booker J, Luschnig C, Leyser O:The Arabidopsis MAX pathway controls shoot branching byregulating auxin transport. Curr Biol 2006, 16:553-563.
22.�
Brewer PB, Dun EA, Ferguson BJ, Rameau C, Beveridge CA:Strigolactone acts downstream of auxin to regulate budoutgrowth in pea and Arabidopsis. Plant Physiol 2009,150:482-493.
This study shows the complexity of strigolactone signaling in the axillarybud and how the interplay of hormones will be essential to understandingthis developmental response. This study also marks the new era ofstudying branching in plants in the context of knowing that the branchingsignal is strigolactones.
23. Stirnberg P, van De Sande K, Leyser HM: MAX1 and MAX2control shoot lateral branching in Arabidopsis. Development2002, 129:1131-1141.
24. Santer A, Estelle M: Recent advances and emerging trends inplant hormone signalling. Nature 2009, 459:1071-1078.
www.sciencedirect.com
Strigolactones: a new hormone with a past Tsuchiya and McCourt 561
25. Shen H, Luong P, Huq E: The F-box protein MAX2 functions as apositive regulator of photomorphogenesis in Arabidopsis.Plant Physiol 2007, 145:1471-1483.
26. Woo HR, Chung KM, Park JH, Oh SA, Ahn T, Hong SH, Jang SK,Nam HG: ORE9, an F-box protein that regulates leafsenescence in Arabidopsis. Plant Cell 2001, 13:1779-1790.
27. Simons JL, Napoli CA, Janssen BJ, Plummer KM, Snowden KC:Analysis of the decreased apical dominance genes of petuniain the control of axillary branching. Plant Physiol 2007,143:697-706.
28.��
Arite T, Umehara M, Ishikawa S, Hanada A, Maekawa M,Yamaguchi S, Kyozuka J: d14, A strigolactone insensitivemutant of rice shows an accelerated outgrowth of tillers.Plant Cell Physiol 2009. [Epub ahead of print].
www.sciencedirect.com
This study again shows the power of the rice dwarf system to identify newmutants in strigolactone biosynthesis and signaling. Possibly like GAsignaling studies, rice will have advantages of other systems such asArabidopsis with respect to dissecting the molecular basis of this newhormone.
29. Bradow J, Connick WJ, Pepperman AB: Comparison of the seedgermination effects of synthetic analogs of strigol, gibberellicacid, cytokinins, and other plant growth regulators.J Plant Growth Regul 1988, 7:227-239.
30. Bradow J, Connick WJ, Pepperman AB, Wartelle LH: Gernminationstimulation in wild oats (Avena fatua L.) by strigol analogs andgibberellic acid. J Plant Growth Regul 1990, 9:35-41.
31. Koornneef M, Bentsink L, Hilhorst H: Seed dormancy andgermination. Curr Opin Plant Biol 2002, 5:33-36.
Current Opinion in Plant Biology 2009, 12:556–561