Abstract: Floral zygomorphy is thought of as an essential adaptation to specific pollinators. The CYCLOIDEA (CYC)-like genes belonging to the plant-specific TCP transcription factor family are the key regulators of floral zygomorphy. Their expression differentiations bring about diverse forms of floral zygomorphy. However, the regulatory mechanism underlying their expression differentiation remains unknown. In this study, we selected Chirita pumila D. Don, a zygomorphic member of Gesneriaceae, as a model to address this question. Mutant analysis shows that the CYC gene in C. pumila (CpCYC) plays an important role in controlling floral zygomorphy. Further functional investigation of CpCYC intron and 5′ regulatory regions indicates that an 899 bp promoter region is a key determinant of the dorsal-specific expression of CpCYC. In this region, using electrophoretic mobility shift assay and transient expression system, we identified three kinds of cis-regulatory elements with putative binding factors, that is, auxin responsive element, WRKY binding site, LEAFY binding site, and an element with an unknown binding factor. We undertook functional analyses of the two putative LEAFY binding sites, and found that LEAFY could directly activate and regulate CpCYC for its dorsal-specific expression in patterning floral zygomorphy. This research would shed significant light on the regulatory and evolutionary pathways underlying the spatial-specific expression of CYC-like genes for the development of zygomorphic flowers.

Key words: Chirita pumila, CpCYC, floral zygomorphy, regulatory pathways, transgenic line