SlWRKY6-dependent melatonin signaling regulates photosynthesis to confer cold tolerance in tomato.

key messageRNA-seq and virus-induced gene silencing experiments have demonstrated that the transcription factor SlWRKY6 affects tomato cold tolerance by responding to melatonin signaling and influencing photosynthesis. Cold stress severely impairs photosynthesis, limiting tomato growth during off-season cultivation. Melatonin (MT) has been shown to enhance plant cold tolerance, yet its regulatory mechanism for maintaining photosynthetic performance remains unclear. In this study, we demonstrated that MT treatment improved the photochemical efficiency of photosystem II (PSII) and stabilized the Calvin cycle under cold stress, thereby enhancing electron transfer, CO₂ fixation, and overall photosynthetic capacity. Notably, transcriptome analysis identified SlWRKY6 as a melatonin-responsive transcription factor that positively regulates photosynthesis under cold conditions. Functional validation using virus-induced gene silencing (VIGS) revealed that silencing SlWRKY6 significantly suppressed photosynthesis-related gene expression, impaired photochemical reactions, and reduced carbon assimilation, ultimately decreasing cold tolerance. Importantly, exogenous MT application was able to partially restore these photosynthetic processes, even under SlWRKY6 silencing. These findings highlight that MT may enhance cold tolerance in tomato via SlWRKY6 as a key regulatory node through modulating the photosynthetic pathway, providing new insights into MT-mediated cold stress adaptation mechanisms in crops.