Homeotic Genes Directing Flower Development in Antirrhinum
Homeotic mutants have been used to define the genetic interactions controlling flowering in Antirrhinum. Three categories of homeotic genes were identified by transposon mutagenesis. The first includes floricaula (flo), which is required to switch inflorescence meristems to floral. This gene has been isolated and shown to be expressed transiently in bract, sepal, petal and carpel primordia. The second group of genes controls the identity (and sometimes the number) of organs in a whorl. These genes affect overlapping whorls and their mutant phenotypes suggest a combinatorial model for gene action in determining the fate of floral primordia. Genes of the third category determine the identity of organs within one whorl and thus affect the symmetry of the flower. We propose that the interactions of these homeotic genes not only control the basic patterns of inflorescence and flower development in Antirrhinum, but possibly in a diverse range of plant species.
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