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The identity of floral organs in Arabidopsis thaliana is determined by homeotic genes, which are expressed in specific regions of the developing flower. The initial activation of homeotic genes is accomplished at least in part by the products of two earlier acting genes with overlapping functions. These are the floral meristem-identity genes LEAFY and APETALA1. The requirements of LEAFY and APETALA1 activity vary for different homeotic genes.
Weigel et al. (1993) studied this question.