Redundant regulation of meristem identity and plant architecture by FRUITFULL, APETALA1 and CAULIFLOWER

The transition from vegetative to reproductive phases during Arabidopsis de velopment is the result of a complex interaction of environmental and endog enous factors. One of the key regulators of this transition is LEAFY (LFY), whose threshold levels of activity are proposed to mediate the initiation of flowers. The closely related APETALA1 (AP1) and CAULIFLOWER (CAL) merist em identity genes are also important for flower initiation, in part because of their roles in upregulating LFY expression. We have found that mutation s in the FRUITFULL (FUL) MADS-box gene, when combined with mutations in AP1 and GAL, lead to a dramatic non-flowering phenotype in which plants contin uously elaborate leafy shoots in place of flowers. We demonstrate that this phenotype is caused both by the lack of LFY upregulation and by the ectopi c expression of the TERMINAL FLOWER1 (TFL1) gene. Our results suggest that the FUL, AP1 and CAL genes act redundantly to control inflorescence archite cture by affecting the domains of LFY and TFL1 expression as well as the re lative levels of their activities.