Evolutionary diversification of CYC/TB1 -like TCP homologs and their recruitment for the control of branching and floral morphology in Papaveraceae (basal eudicots)

Angiosperms possess enormous morphological variation in plant architectures and floral forms. Previous studies in Pentapetalae and monocots have demonstrated the involvement of TCP domain CYCLOIDEA/TEOSINTE BRANCHED1-like (CYC/TB1) genes in the control of floral symmetry and shoot branching. However, how TCP/CYC-like (CYL) genes originated, evolved and functionally diversified remain unclear. We conducted a comparative functional study in Ranunculales, the sister lineage to all other eudicots, between Eschscholzia californica and Cysticapnos vesicaria, two species of Papaveraceae with actinomorphic and zygomorphic flowers, respectively. Phylogenetic analysis indicates that CYL genes in Papaveraceae form two paralogous lineages, PapaCYL1 and PapaCYL2. Papaveraceae CYL genes show highly diversified expression patterns as well as functions. Enhanced branching by silencing of EscaCYL1 suggests that the role of CYC/TB1-like genes in branching control is conserved in Papaveraceae. In contrast to the arrest of stamen development in Pentapetalae, PapaCYL genes promote stamen initiation and growth. In addition, we demonstrate that CyveCYLs are involved in perianth development, specifying sepal and petal identity in Cysticapnos by regulating the B-class floral organ identity genes. Our data also suggest the involvement of CyveCYL genes in the regulation of flower symmetry in Cysticapnos. Our work provides evidence of the importance of TCP/CYC-like genes in the promotion of morphological diversity across angiosperms.