Genome-Wide Identification, Expression Analysis and Functional Study of CCT Gene Family in Medicago truncatula

The control of flowering time has an important impact on biomass and the environmental adaption of legumes. The CCT (CO, COL and TOC1) gene family was elucidated to participate in the molecular regulation of flowering in plants. We identified 36 CCT genes in the M. truncatula genome and they were classified into three distinct subfamilies, PRR (7), COL (11) and CMF (18). Synteny and phylogenetic analyses revealed that CCT genes occurred before the differentiation of monocot and dicot, and CCT orthologous genes might have diversified among plants. The diverse spatial-temporal expression profiles indicated that MtCCT genes could be key regulators in flowering time, as well as in the development of seeds and nodules in M. truncatula. Notably, 22 MtCCT genes with typical circadian rhythmic variations suggested their different responses to light. The response to various hormones of MtCCT genes demonstrated that they participate in plant growth and development via varied hormones dependent pathways. Moreover, six MtCCT genes were dramatically induced by salinity and dehydration treatments, illustrating their vital roles in the prevention of abiotic injury. Collectively, our study provides valuable information for the in-depth investigation of the molecular mechanism of flowering time in M. truncatula, and it also provides candidate genes for alfalfa molecular breeding with ideal flowering time.