Figure 1

Independent recruitment of CYC-like genes for the evolution of floral zygomorphy and stamen reduction. (a) Images and diagrams of flowers of several Lamiales lineages, illustrating the diversity in stamen reduction. Antirrhinum, Mohavea, Veronica and Gratiola are members of the Plantaginaceae; Opithandra is a member of the Gesneriaceae. Shading indicates the approximate expression of at least one CYC-like TCP homolog in each of these lineages; X indicates the presence of a staminode. In Veronica, Gratiola and Opithandra, at least one other close paralog of the CYC-like gene whose expression is illustrated has a highly divergent pattern of expression [2, 11]. In Mohavea and Opithandra, expression correlates with additional stamen reduction compared with Antirrhinum. In Veronica and Gratiola, there is no correlation between CYC-like gene expression and additional stamen reduction. In Veronica, staminodes are absent in the dorsal and ventral flower regions where stamen loss is inferred. (b) Three of many independent transitions from radial floral symmetry to bilateral symmetry across the core eudicot lineage are indicated in bold. Functional studies of A. majus [4], L. japonicus [7], P. sativum [8] and I. amara [9] have demonstrated that developmental genetic pathways using CYC-like TCP genes have been independently recruited to establish bilateral flower symmetry. The photograph of Opithandra in (a) isreproduced with permission from [2].