Tomato CONSTANS-Like1 promotes anthocyanin biosynthesis under short day and suboptimal low temperature

Plant growth and development are precisely controlled by light and temperature during their life span. However, the mechanism by which photoperiod and seasonal changes influence the physiological response of day-neutral plants, such as tomato (Solanum lycopersicum), remains unclear. Here, we found that the tomato CONSTANS (CO) close homolog, CONSTANS-Like1 (SlCOL1), does not affect the flowering of tomato under either long-day or short-day conditions. However, CRISPR/Cas9-mediated editing of SlCOL1 showed a much lower anthocyanin accumulation in mutant than in wild-type plants, especially under SD at suboptimal low-temperature conditions. SlCOL1 directly activated the Hoffman's Anthocyanin 1 (SlAN1) promoter and interacted with SlAN1 to promote anthocyanin biosynthesis under SD. The cold-induced upregulation of SlCOL1 further promoted anthocyanin accumulation and enhanced reactive oxygen species scavenging under SD at low-temperature conditions. These results reveal that the SlCOL1-SlAN1 module collaboratively regulates anthocyanin accumulation under SD and cold conditions, which could help tomato counteract the cold autumn/winter season in nature.