Flower Meristem Identity

Flower Meristem Identity

Meristem Identity Genes can be divided into two distinct classes. The first class promotes flower meristem identity, and includes LEAFY, APETALA1 and CAULIFLOWER together with UNUSUAL FLORAL ORGANS (UFO), and others. The second class has the opposite effect, and maintains the identity of inflorescence shoot meristems, and includes TERMINAL FLOWER.	Related Links UFO LEAFY APETALA1 CAULIFLOWER APETALA2
In general, mutations in meristem identity genes such as LFY and AP1 lead to a partial conversion of flowers into shoots, whereas mutations in TFL cause both early flowering and premature conversion of the normally indeterminate shoot meristem into a flower meristem, with the resulting formation of a terminal flower. TFL can be considered a negative spatial regulator of both LFY and AP1, since mutations in TFL lead to ectopic activity of both LFY and AP1 and the tfl phenotype can be largely suppressed if both the LFY and AP1 genes are inactivated. Although lfy and ap1 mutants display partial conversion of flowers into shoots, this phenotype is dramatically enhanced in lfy ap1 double mutants such that a nearly complete conversion of flowers into shoots occurs.
	Meristem Identity mutants A. lfy flower B. lfy inflorescence C. ap1 flower D. lfy ap1 inflorescence E. tfl flower & whole plant
Additionally, LFY and AP1 are each sufficient to promote flower initiation, since ectopic expression of either gene from the CaMV35S promoter largely replaces shoots with individual flowers.
The role of the CAL gene largely overlaps with that of AP1, such that cal single mutants are not significantly different from wild-type, whereas mutations in the CAL gene dramatically enhance the phenotype of ap1 mutants causing a massive proliferation of "inflorescence-like' meristems in place of flowers.	ap1cal double mutant
The phenotypes conferred by mutations in meristem identity genes are sensitive to environmental factors such as temperature and day length. For example, short days or low temperatures, which attenuate floral induction, enhance the phenotype of flower meristem identity mutants but suppress the phenotype of tfl mutants. Thanks to Detlef Weigel for the lfy and ap1 lfy mutant photos.
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