FLOWERING-TIME GENES MODULATE THE RESPONSE TO LEAFY ACTIVITY

Among the genes that control the transition to flowering in Arabidopsi s is a large group whose inactivation causes a delay in flowering. It has been difficult to establish different pathways in which the flower ing-time genes might act, because mutants with lesions in these genes have very similar phenotypes. Among the putative targets of the flower ing-time genes is another group of genes, which control the identity o f individual meristems. Overexpression of one of the meristem-identity genes, LEAFY, can cause the precocious generation of flowers and thus early flowering. We have exploited the opposite phenotypes seen in la te-flowering mutants and LEAFY overexpressers to clarify the genetic i nteractions between flowering-time genes and LEAFY. According to epist atic relationships, we can define one class of flowering-time genes th at affects primarily the response to LEAFY activity, and another class of genes that affects primarily the transcriptional induction of LEAF Y. These observations allow us to expand previously proposed models fo r the genetic control of flowering time.