Molecular evolution of the transcription factor LEAFY in Brassicaceae

LEAFY (LFY) is a DNA-binding transcription factor that regulates floral meristem identity. LFY is unusual among angiosperm developmental regulators because it is not part of an extended gene family. Recent expression studies and transgenic experiments have suggested that changes at the LFY locus might have played a role in the evolution of rosette flowering, a modified plant architecture that has evolved at least three times in Brassicaceae. Here we examined the sequences of LFY genes from 16 species of Brassicaceae to evaluate whether gene duplication and/or the shift to rosette flowering correlate with changes in the molecular evolution of LFY. We found evidence of gene duplication in four taxa, but phylogenetic analysis suggested that duplicate genes have generally not persisted through multiple speciation events. This result can be explained if LFY is prone to be lost by drift due to a low probability of subfunctionalization or neofunctionalization. Despite great heterogeneity in dN/dS ratios, duplicate genes show a significant tendency to have elevated dN/dS ratios. Rosette-flowering lineages also show elevated dN/dS ratios and two of the rosette-flowering taxa, Idahoa and Leavenworthia, have some radical amino acid substitutions that are candidates for having played a causal role in the evolution of rosette flowering.