Exogenous Methylation Inhibitor 5-Azacytidine Accelerates Postharvest Leaf Senescence in Pak Choi by Modulating Transcriptomic and Metabolomic Profiles

Abstract

The senescence of leafy vegetables is inherent and general after harvest. DNA methylation affects the senescence process of plant leaves. Limited studies have explored the impact of exogenous methylation inhibitors on postharvest vegetables and the mechanisms of their effects on the transcriptome and metabolome during storage. In this study, pak choi was immersed in 100 mg L⁻¹ of 5-azacytidine (AZ) (an inhibitor of methyltransferase) solutions, indicated that AZ yielded significant acceleration in leaf senescence. Compared to the control group, the AZ-treated pak choi exhibited faster weight loss, higher malondialdehyde content, greater color change, and higher chlorophyllase activity. Transcriptomic and widely targeted metabolomic analyses were then performed on pak choi samples. Transcriptomic investigation disclosed that the chlorophyll degradation genes BraSGR2 and BraPPH were upregulated by AZ, leading to the degradation of more chlorophyll content. AZ effectively stimulated upregulation of the senescence-associated genes (BraSAG20, BraSAG21, BraSRG1, and BraSRG2), thereby accelerating the pace of the senescence process. The widely targeted metabolomic analyses demonstrated that AZ downregulated the flavonoid synthase genes BraFLS1 and BraF3H, causing a relative decline in flavonoid levels. The study also unveiled a diminution in carbohydrate content during storage, further exacerbated by AZ. To encapsulate, our preliminary findings suggest that the application of AZ effectively accelerates the process of leaf senescence in stored pak choi, which helps us understand the relationship between DNA demethylation and vegetable senescence.