Anthocyanins are pigment molecules commonly found in red, blue, and purple flowers. Columbine flowers are imbued with anthocyanins, and this plant is known to have undergone a recent and rapid divergence, most likely as a result of strong selection by pollinators for floral traits such as color.
Using a phylogenetic framework, Whittall et al. have investigated the convergent loss--that is, the loss of the same trait across multiple evolutionary lineages--of anthocyanin biosynthesis in columbines, which has resulted in flowers that are yellow or white. They found six independent losses (four fixed and two polymorphic) and no gains of floral anthocyanins. Quantitating the anthocyanin precursors in three species without anthocyanin loss and eight species with loss demonstrated that the loss of anthocyanin correlated with a broad convergence in the reduced expression of genes that occur in the later stages of the biosynthetic pathway. Additionally, two of these genes are regulated by a single gene and demonstrated a correlated reduction of expression in five lineages, suggesting that the mutation causing anthocyanin loss is a regulatory component and not a structural one (enzyme). These data show that there is an evolutionary constraint on some of the genes in anthocyanin biosynthesis, most likely because upstream intermediates are also useful in protecting plants against UV damage, insects, and pathogens. -- LMZ
Mol. Ecol. 15, 4645 (2006).
