Abstract
BACKGROUND: The attractive inflorescence of Chrysanthemum morifolium, its capitulum, is always composed of ray (female, zygomorphy) and disc (bisexual, actinomorphy) florets, but the formation mechanism remains elusive. The gene diversification pattern of the ECE (CYC/TB1) clade has been speculated to correlate with the capitulum. Within the three subclades of ECE, the involvement of CYC2 in defining floret identity and regulating flower symmetry has been demonstrated in many species of Asteraceae, including C. morifolium. Differential expression of the other two subclade genes, CYC1 and CYC3, in different florets has been reported in other Asteraceae groups, yet their functions in flower development have not been investigated. METHODS: Here, a CYC1 gene, CmCYC1a, was isolated and its expression pattern was studied in C. morifolium. The function of CmCYC1a was identified with gene transformation in Arabidopsis thaliana and yeast two-hybrid (Y2H) assays were performed to explore the interaction between CmCYC1 and CmCYC2. RESULTS: CmCYC1a was expressed at higher levels in disc florets than in ray florets and the expression of CmCYC1a was increased in both florets during the flowering process. Overexpression of CmCYC1a in A. thaliana changed flower symmetry from actinomorphic to zygomorphic, with fewer stamens. Furthermore, CmCYC1a could interact with CmCYC2b, CmCYC2d, and CmCYC2f in Y2H assays. CONCLUSIONS: The results provide evidence for the involvement of CmCYC1a in regulating flower symmetry and stamen development in C. morifolium and deepen our comprehension of the contributions of ECE genes in capitulum formation.