Conserved CO-FT Module Regulating Flowering Time in Chrysanthemum indicum L.

Chrysanthemum indicum L. is widely used in China for significant medicinal value. However, its pharmacological activities were unstable as a result of unreliable flowering time. To study the regulation of flowering time in C. indicum, we cloned the two FT-like genes from C. indicum, which were localized in the cytoplasm and nucleus of tobacco epidermal cells. Phylogenetic relationship analysis showed they were highly conserved and the CiFTL1 gene was strongly induced by short-days. Dual-luciferase assays found that CiCO could specifically bind to the promoter of CiFTL1, but could not directly interact with CiFTL2. Moreover, a CO-responsive element (CORE), localizing between -630 and -430 nucleotides from the ATG, was essential for the CiFT1 gene expression in the flowering process. Therefore, the TGTG(N2-N3)ATG was crucial for CiCO recruitment rather than the CCAAT box, which suggested the CO/FT regulatory module might be conserved in C. indicum. The research will provide sufficient information for revealing regulatory mechanisms of flowering time in C. indicum.