Plant growth and development are precisely regulated by light and temperature throughout their life cycles. Based on their requirements for daylight length to flower, plants can be classified into three categories: long-day plants (e.g., Arabidopsis), short-day plants (e.g., rice), and day-neutral plants (e.g., tomato). However, the mechanisms by which photoperiod and seasonal changes influence the physiological responses of day-neutral plants, such as tomatoes (Solanum lycopersicum), remain unclear.

Previous studies have shown that CONSTANS (CO) is a vital regulatory factor in the photoperiod response of plants and plays a central role in regulating flowering. Nevertheless, comprehensive research on the molecular functions of CO and its close homolog, CONSTANS-Like1 (SlCOL1), in photoperiod-insensitive plants is still lacking.

To address this gap, a research team led by Prof. DENG Shulin from the South China Botanical Garden of the Chinese Academy of Sciences discovered that SlCOL1 does not influence the flowering time of tomatoes under long-day (LD) and short-day (SD) conditions. The results indicated that anthocyanin accumulation in tomato leaves was significantly increased under short-day conditions, while the anthocyanin content in the leaves of the SlCOL1 mutant was considerably lower than that of the wild type.

Using dual-luciferase reporter assays (Dual-LUC), yeast one-hybrid assays (Y1H), electrophoretic mobility shift assays (EMSA), and chromatin immunoprecipitation quantitative PCR (ChIP-qPCR), the study showed that SlCOL1 can directly bind to the G-box1 element of the Hoffman's Anthocyanin 1 (SlAN1) promoter, which is a key gene in anthocyanin biosynthesis within the MBW complex, thereby activating its expression.

Additionally, it was confirmed that SlCOL1 interacts with SlAN1, enhancing anthocyanin biosynthesis by promoting the expression of structural genes involved in anthocyanin production.

Short-day conditions are often accompanied by lower temperatures, particularly in autumn in the northern hemisphere. The expression level of SlCOL1 can be significantly up-regulated under these short-day and suboptimal low-temperature conditions (15°C). The increased accumulation of SlCOL1 further promotes anthocyanin accumulation, which helps to scavenge reactive oxygen species (ROS) in tomatoes, aiding their adaptation to autumn environmental conditions.

This study was published in Plant Physiology and received support from grants from the National Natural Science Foundation of China, the Natural Science Foundation of Guangdong Province, and the Guangdong Science and Technology Plan Project.