Conservation and diversification of the symmetry developmental program among close relatives of snapdragon with divergent floral morphologies

Multiple evolutionary shifts in floral symmetry and stamen number have occurred in the snapdragon (Antirrhinum majus) family Veronicaceae. In Mohavea, Veronica and Gratiola there have been independent evolutionary reductions in stamen number and modifications to corolla shape. It is hypothesized that changes in the regulation of homologs of snapdragon dorsal flower identity genes CYCLOIDEA (CYC) and RADIALIS (RAD) underlie these floral transitions. CYC-like and RAD-like genes from Veronica montana and Gratiola officinalis were cloned and sequenced, compared with homologs from other Veronicaceae species using phylogenetic analysis, and their expression was investigated by reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization. VmCYC1, GoCYC1, GoCYC2 and RAD-like genes are expressed exclusively in the dorsal region of floral meristems and developing flowers. Their expression patterns do not correlate with patterns of stamen arrest. VmCYC2 and GoCYC3 are expressed in both vegetative and floral tissues, with VmCYC2 being most abundant in all regions of the floral meristem and all petals. These results support conservation of the floral symmetry gene network for Veronicaceae RAD-like and some CYC-like paralogs, suggest regulatory evolution of other CYC-like genes following gene duplication and implicate different genetic mechanisms underlying dorsal versus ventral stamen abortion within Veronica and Gratiola. New Phytologist (2009) 182: 751-762doi: 10.1111/j.1469-8137.2009.02794.x.