Rapid molecular evolution of CYCLOIDEA-like genes in Antirrhinum and its relatives.

The CYCLOIDEA (CYC) and DICHOTOMA (DICH) genes encode related TCP transcription factors that control floral asymmetry in Antirrhinum majus. Analysis of sequences from relatives of Antirrhinum suggested that CYC and DICH arose from a gene duplication in an ancestor of the tribe Antirrhineae and have subsequently evolved at similar rates. Coding regions outside the conserved functional TCP and R domains differed by numerous indels, suggesting rapid evolution and low constraint on amino acid sequence. An analysis of variability within the genus Antirrhinum revealed very similar CYC alleles in 17 representative species, consistent with most of the species having diverged within the last 1 myr. Whereas substitution mutations appear to have accumulated constantly, one Antirrhinum CYC allele provided evidence for sporadic and rapid accumulation of insertion mutations.