Abstract: CYC-like genesarewidely conserved in controlling floral dorsoventral asymmetry (zygomorphy) through persistent expressions in corresponding domains in core eudicots.To understand how CYC-like gene expressionsare maintained during flower development, we selected Chirita heterotrichaas materials andisolatedthe promoter sequences of ChCYC1C and ChCYC1D genes, homologs of CYC, by inverse PCR. Further promoter analyses led to the identification of a putative cis-regulatory element in each promoter matching the consensus DNA binding site for Antirrhinum CYC protein: GGCCCCTC at –165 for ChCYC1C, and GGCCCCCC at –163 for ChCYC1D. This result indicates that both ChCYC1C and ChCYC1D genes probably have evolved autoregulatory loops to sustain their expressions in developing flowers. We also isolated the coding and promoter sequences of ChRAD gene, a homolog of Antirrhinum RAD. Promoter analysis showed that ChRAD gene promoter also contained a putative CYC-binding site (GGCCCAC at –134). Therefore, ChRAD is likely a direct target of ChCYC1 genes, which is similar to Antirrhinum RAD. The above results imply that the establishment of floral zygomorphy in Chirita might have been achieved by the evolution of autoregulatory loop of CYC-like genes, which was probably accompanied by simultaneous co-option of RAD-like gene into their regulatory network.

Key words: autoregulatory loop, Chirita heterotricha, CYC-binding sites, CYCLOIDEA, RADIALIS.