Melatonin retards leaf senescence by modulating phytohormones metabolism in stored Chinese flowering cabbage

Abstract This paper was conducted to explore the effects of melatonin (MT) on the senescence of stored Chinese flowering cabbage and the potential modulatory mechanisms involved. The physiological findings demonstrated that MT successfully reduced chlorophyll loss and improved the photochemical effectiveness of cabbage leaves. In addition, MT decreased the transcription of senescence-associated genes (BrSAG12) and genes responsible for chlorophyll breakdown. Transcriptome analysis showed that MT-regulated genes were enriched in oxidative phosphorylation, hormone metabolism and signal transduction, and MT treatment reduced the high expression of genes linked to generation of reactive oxygen species (ROS), energy metabolism, phytohormone (abscisic acid (ABA), ethylene (ET), and jasmonic acid (JA)) biological synthesis and signal transduction while promoting the activation of genes related to scavenging ROS, energy biosynthesis and plant–pathogen interactions. We emphasized the examination of the potential interaction between phytohormone metabolism and MT. The results showed that the application of MT decreased ABA, ET, and JA levels as well as the expression of their biosynthesis genes, concurrently maintaining higher expression of cytokinin, auxin and gibberellin biosynthetic genes and lower expression of degradation genes. Regulatory networks of transcription factors (TFs) and genes related to ABA, ET and JA metabolism showed that TFs such as DNA-binding One Zinc Finger 5.7 (DOF5.7), WRKY40, and homeobox-leucine zipper protein-16 (ATHB-16) might play important transcriptional regulatory roles in mediating MT postponed leaf senescence. Taken together, these findings suggested that the postponed senescence of cabbage treated with MT might be ascribed to the regulated oxidative phosphorylation, energy, phytohormone metabolism, and transcription factors.