Methylation histology reveals the molecular mechanism by which red light-mediated DNA methylation delays leaf senescence in Pak Choi (Brassica rapa subsp. chinensis)

Leaf senescence is a key factor affecting the post-harvest quality and shelf life of vegetables. The specific mechanisms by which light environment and DNA methylation mediate leaf senescence remain unclear. This study explored the molecular mechanism by which red LED light (RL) delays leaf senescence through DNA methylation in Pak Choi (Brassica rapa subsp. chinensis). In this study, RL treatment significantly suppressed leaf senescence in Pak Choi during postharvest storage and downregulated the expression of senescence-associated genes (SAGs). Experiments with methylation inhibitors confirmed its association with DNA methylation. Furthermore, whole-genome bisulfite sequencing (WGBS) revealed that during storage-induced senescence, Pak Choi exhibited significantly reduced methylation levels across its genome, particularly in promoter regions, and RL treatment reversed this effect. Furthermore, virus-induced gene silencing (VIGS) and overexpression (OE) experiments confirmed the central role of the demethylase BrDML3 (BraA01g004250.3.5C) in this process. Subsequently, a transcription factor under its regulation, BrNAC55 (BraA05g032630.3.5C), was identified and shown to promote leaf senescence by activating downstream SAGs (BrSGR1, BrPPH, BrSAUR36) to promote leaf senescence. In addition, this study found that BrNAC55 can also form a feedback loop with BrDML3, continuously amplifying leaf senescence. This study elucidates the mechanism by which RL-mediated DNA methylation delays leaf senescence, providing a foundation for postharvest preservation technologies.