CONTROL OF FLOWER DEVELOPMENT IN ARABIDOPSIS-THALIANA BY APETALA1 ANDINTERACTING GENES

Mutations in the APETALA1 gene disturb two phases of flower developmen t, flower meristem specification and floral organ specification. These effects become manifest as a partial conversion of flowers into inflo rescence shoots and a disruption of sepal and petal development. We de scribe the changes in an allelic series of nine apetala1 mutants and s how that the two functions of APETALA1 are separable. We have also stu died the interaction between APETALA1 and other floral genes by examin ing the phenotypes of multiply mutant plants and by in situ hybridizat ion using probes for several floral control genes. The results suggest that the products of APETALA1 and another gene, LEAFY, are required t o ensure that primordia arising on the flanks of the inflorescence ape x adopt a floral fate, as opposed to becoming an inflorescence shoot. APETALA1 and LEAFY have distinct as well as overlapping functions and they appear to reinforce each other's action. CAULIFLOWER is a newly d iscovered gene which positively regulates both APETALA1 and LEAFY expr ession. All functions of CAULIFLOWER are redundant with those of APETA LA1. APETALA2 also has an early function in reinforcing the action of APETALA1 and LEAFY, especially if the activity of either is compromise d by mutation. After the identity of a flower primordium is specified, APETALA1 interacts with APETALA2 in controlling the development of th e outer two whorls of floral organs.