Developmental genetics of floral symmetry evolution.

The relative importance of convergence and parallelism in the independent evolution of similar traits remains an important question in evolutionary biology. Floral zygomorphy has evolved multiple times independently in different plant lineages through alterations in size, shape and/or number of spatially defined organs. In Antirrhinum majus (snapdragon) floral zygomorphy is controlled by CYCLOIDEA and DICHOTOMA, two recently duplicated TCP transcription factors that determine dorsal identity through their interaction with MYB and cell-cycle genes. Early on it was speculated that independent evolutionary transitions from floral actinomorphy to zygomorphy would probably result from unique developmental genetic mechanisms. Here, we review recent evidence supporting the parallel recruitment of CYCLOIDEA homologs in independent evolutionary transitions to zygomorphy in distantly related core eudicot lineages.