Conservation of floral homeotic gene function between Arabidopsis and antirrhinum

Several homeotic genes controlling floral development have been isolated in both Antirrhinum and Arabidopsis. Based on the similarities in sequence and in the phenotypes elicited by mutations in some of these genes, it has been proposed that the regulatory hierarchy controlling floral development is comparable in these two species. We have performed a direct experimental test of this hypothesis by introducing a chimeric Antirrhinum Deficiens (DefA)/Arabidopsis APETALA3 (AP3) gene, under the control of the Arabidopsis AP3 promoter, into Arabidopsis. We demonstrated that this transgene is sufficient to partially complement severe mutations at the AP3 locus. In combination with a weak ap3 mutation, this transgene is capable of completely rescuing the mutant phenotype to a fully functional wild-type flower. These observations indicate that despite differences in DNA sequence and expression, DefA coding sequences can compensate for the loss of AP3 gene function. We discuss the implications of these results for the evolution of homeotic gene function in flowering plants.