REGULATION OF THE ARABIDOPSIS FLORAL HOMEOTIC GENE APETALA1

The Arabidopsis floral homeotic gene APETALA1 (AP1) encodes a putative transcription factor that acts locally to specify the identity of the floral meristem and to determine sepal and petal development. RNA tis sue in situ hybridization studies show that AP1 RNA accumulates unifor mly throughout young floral primordia, but is absent from the inflores cence meristem. Later in development, AP1 RNA is excluded from cells t hat will give rise to the two inner whorls of organs. Here we show tha t AP1 expression is under the control of two negative regulators: the meristem identity gene TERMINAL FLOWER represses AP1 RNA accumulation in the inflorescence meristem, and the organ identity gene AGAMOUS pre vents AP1 RNA accumulation in the two inner whorls of wild-type flower s. These and other data presented here lead to a revised model for the regulatory interactions among the genes specifying floral organ ident ity in Arabidopsis.