Analysis of interaction between mutations abruptus and leafy and previous data on interactions of abruptus with homeotic mutations apetalal, apetala2, and apetala3 showed that the functions of the ABRUPTUS/PINOID (ABR/PID) gene are as follows: (1) it determines position of lateral organs on the inflorescence without specifying their identity [floral meristem (FM) or cauline leaves]; (2) in concert with the LEAFY(LFY) gene, it participates in the formation of FM; (3) it is involved in the determination and the formation of floral organ primordia in the first, second, and third whorls. Auxin accumulation in the abr mutant cells in callus culture was shown indicating the involvement of the ABR/PID gene in regulation of auxin efflux from cells. It is suggested that the ABR/PID expression in the sites of formation of FM and floral organs leads to local reduction in auxin level and/or activation of the lateral auxin flow, which in turn, enhance expression of the LFY and homeotic genes responsible for FM formation and differentiation.