Uncovering genetic and molecular interactions among floral meristem identity genes in Arabidopsis thaliana.

The inflorescence meristem produces floral primordia that remain undifferentiated during the first stages of flower development. Genes controlling floral meristem identity include LEAFY (LFY), APETALA1 (AP1), CAULIFLOWER (CAL), LATE MERISTEM IDENTITY 1 (LMI1), SHORT VEGETATIVE PHASE (SVP) and AGAMOUS-LIKE24 (AGL24). The lfy mutant shows partial reversions of flowers into inflorescence shoot-like structures and this phenotype is enhanced in the lfy ap1 double mutant. Here we show that combining the lfy mutant with agl24 and svp single mutants or with the agl24 svp double mutant enhances the lfy phenotype and that the lfy agl24 svp triple mutant phenocopies the lfy ap1 double mutant. Analysis of the molecular interactions between LFY, AGL24 and SVP showed that LFY is a repressor of AGL24 and SVP, whereas LMI1 is a positive regulator of these genes. Moreover, AGL24 and SVP positively regulate AP1 and LFY by direct binding to their regulatory regions. Since all these genes are important for establishing floral meristem identity, regulatory loops are probably important to maintain the correct relative expression levels of these genes.