Time to stop: flower meristem termination - PubMed (original) (raw)
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Time to stop: flower meristem termination
Nathanaël Prunet et al. Plant Physiol. 2009 Aug.
No abstract available
Figures
Figure 1.
Diagrams of wild-type and mutant Arabidopsis flowers displaying supernumerary organs. A, Wild-type flowers consist of four whorls bearing four sepals, four petals, six stamens, and two fused carpels, respectively. B, Weak clv and ult1 mutant flowers exhibit supernumerary organs contained within the four primary whorls. C, Strong _ag_-1 mutant flowers are indeterminate, with numerous supernumerary whorls of organs and homeotic transformations of reproductive organs into perianth ones. D, Weak _ag_-4 mutant flowers are also indeterminate, with numerous supernumerary whorls of stamens and sepals. E, sup mutant flowers display a limited number of supernumerary whorls of stamens and sometimes staminoid carpels in the center. F, Strong clv and some ult1 mutant flowers display supernumerary organs in each primary whorl but also exhibit a weak loss of FM termination, with a limited number of supernumerary whorls within the gynoecium. G, _sup ag_-1 double mutant flowers display an indefinite number of petals inside the first whorl of sepals. H, _sup ag_-4 double mutants have fully indeterminate male flowers, with the two inner whorls replaced by an indeterminate number of stamens borne on a spiral. Red asterisks indicate totally indeterminate FMs.
Figure 2.
Siliques of wild-type and indeterminate flowers. A, Silique of a wild-type, determinate flower: Placenta develops between the fused carpels and bears ovules, and no floral organs are found within the gynoecium. B, Silique of an indeterminate flower, exhibiting supernumerary floral organs within the gynoecium, due to maintenance of the FM after stage 6; placenta usually develops (not shown), but at a much lesser extent than in wild type, and the seed set is greatly reduced due to the development of these supernumerary organs.
Figure 3.
Main genetic pathways promoting FM termination. FM termination is due to the extinction of WUS expression at stage 6 of flower development, due to its repression by the MADS-box transcription factor AG. To perform this function, AG is required in a subdomain of whorl 4, marked off by gray dots. FM termination also requires the previous exclusion of AP3 and PI, which appear to oppose WUS repression by AG, from whorl 4. This exclusion is mediated by SUP. This may explain why AG, while expressed from stage 3 onwards, fails to shut WUS expression down before stage 6, when carpel primordia emerge. However, this delay was also proposed to be due to a progressive increase in AG expression level during flower development, a high dose of AG being specifically required for FM termination. This sketch represents a stage 6 flower bud, but it is worth noting that SUP's functions occur during earlier developmental stages, but condition the subsequent disruption of stem cell maintenance by AG. Asterisks indicate interactions that are still debated.
Figure 4.
Control of flower determinacy by SUP and class B proteins. A and B, Effects of the sup-1 mutation on class B genes expression pattern. Green staining marks simultaneous expression of AP3 and PI; yellow staining marks that of PI alone. Red arrowheads mark the boundary between whorls 3 and 4. A, mRNA distribution pattern of class B genes AP3 and PI in a wild-type flower at stage 5. At that stage, AP3 and PI are coexpressed in the third whorl, but are excluded from the fourth whorl. B, mRNA distribution pattern of class B genes AP3 and PI in a _sup_-1 mutant flower at stage 5. Compared to wild type, expression of AP3 and PI is expanded in the fourth whorl, toward the FM center. PI mRNA expansion appears wider than that of AP3. C to E, Two models of production of supernumerary stamens in sup-1 mutant flowers. The sketches represent _sup_-1 mutant flowers at stage 5 (C) and 7 (D and E). Different colors are used to follow the evolution of two cell populations, which correspond to two distinct domains of the flower at stage 5, during flower development. Red asterisks mark stamen primordia. C, Blue staining marks the center of the flower, which at this stage corresponds to the FM. Orange staining marks the inner part of whorl 3, which corresponds to SUP expression domain. D, First model: supernumerary stamens are produced from the FM whose termination is delayed. The identity of these supernumerary organs results from the ectopic expression of class B genes in the fourth whorl. E, Second model: supernumerary stamens are produced from the inner part of whorl 3 that overproliferates. Conversely, proliferation within the FM is strongly reduced. The broadening of AP3 and PI mRNA distribution results from an overproliferation of class B-expressing cells rather than from an ectopic expression of these genes. F, Model of competition between B and C proteins to form MADS-box transcription factors complexes. The balance between class B and C proteins directs which MADS-box protein complexes are formed, and which developmental program subsequently takes place. MADS-box proteins are symbolized by colored circles; red, AG; green, AP3; yellow, PI; gray, SEP. For practical reasons, protein complexes are represented as heterotetramers, according to the quartet model (Theissen and Saedler, 2001), though their exact stoichiometry remains unknown. Quartet size indicates their relative amounts.
References
- Alvarez J, Smyth DR (1999) CRABS CLAW and SPATULA, two Arabidopsis genes that control carpel development in parallel with AGAMOUS. Development 126 2377–2386 -PubMed
- Angenent GC, Franken J, Busscher M, Weiss D, van Tunen AJ (1994) Co-suppression of the petunia homeotic gene fbp2 affects the identity of the generative meristem. Plant J 5 33–44 -PubMed
- Bereterbide A, Hernould M, Castera S, Mouras A (2001) Inhibition of cell proliferation, cell expansion and differentiation by the Arabidopsis SUPERMAN gene in transgenic tobacco plants. Planta 214 22–29 -PubMed
- Bowman JL, Sakai H, Jack T, Weigel D, Mayer U, Meyerowitz EM (1992) SUPERMAN, a regulator of floral homeotic genes in Arabidopsis. Development 114 599–615 -PubMed
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