Molecular Evolution of Genes Controlling Petal and Stamen Development: Duplication and Divergence Within the APETALA3 and PISTILLATA MADS-Box Gene Lineages

Abstract

The specification of floral organ identity in the higher dicots depends on the function of a limited set of homeotic genes, many of them members of the MADS-box gene family. Two such genes, <i>APETALA3</i> (<i>AP3</i>) and <i>PISTILLATA</i> (<i>PI</i>), are required for petal and stamen identity in Arabidopsis; their orthologs in Antirrhinum exhibit similar functions. To understand how changes in these genes may have influenced the morphological evolution of petals and stamens, we have cloned twenty-six homologs of the <i>AP3</i> and <i>PI</i> genes from two higher eudicot and eleven lower eudicot and magnolid dicot species. The sequences of these genes reveal the presence of characteristic <i>PI</i>- and <i>AP3</i>-specific motifs. While the <i>PI</i>-specific motif is found in all of the <i>PI</i> genes characterized to date, the lower eudicot and magnolid dicot <i>AP3</i> homologs contain distinctly different motifs from those seen in the higher eudicots. An analysis of all the available <i>AP3</i> and <i>PI</i> sequences uncovers multiple duplication events within each of the two gene lineages. A major duplication event in the <i>AP3</i> lineage coincides with the base of the higher eudicot radiation and may reflect the evolution of a petal-specific <i>AP3</i> function in the higher eudicot lineage.