Abstract
Leaf senescence significantly impacts both the yield and quality of non-heading Chinese cabbage (NHCC). Despite its importance, the molecular mechanisms underlying the initiation and progression of leaf senescence in NHCC remain poorly understood. Here, transcriptome changes are first profiled, and found that ethylene (ET) and salicylic acid (SA) signaling pathways are activated during leaf senescence. Further mining of ET, SA, and DNA methylation pathway genes identified that EIN3A and CMT2 are induced and repressed, respectively, during leaf senescence. A whole-genome bisulfite sequencing (WGBS) analysis revealed a global reduction of DNA methylation during leaf senescence, with the most dramatic decline occurring in the 1 kb regions upstream of transcription start sites (TSS) and downstream of transcription end sites (TES). Knocking down of EIN3A and CMT2 via virus-induced gene silencing (VIGS) demonstrated that EIN3A is crucial for ET- and age-triggered leaf senescence, while CMT2 plays an inhibitory role. It further showed that EIN3A directly represses the expression of CMT2 to release its "braking" role on senescence-associated genes (SAGs) expression. Thus, the study uncovers a pivotal antagonistic interaction between ET signaling and DNA methylation, which may be involved in setting the pace for the progression of leaf senescence in NHCC.