Methyl jasmonate facilitates wound healing of Chinese yam tubers via positively regulating the biosynthesis and polymerization of suberin polyphenolics

Suberin is a cell wall-associated heteropolymer composed of suberin polyaliphatics (SPA) and suberin polyphenolics (SPP), which confers a hydrophobic barrier to plants against dehydration and pathogen invasion. Jasmonic acid (JA) plays a positive role in wound-induced SPP deposition in kiwifruit and potato tubers, but the mechanism underlying the regulation of JA on wound healing of Chinese yam tubers remains unknown. In this study, the biochemical and physiological responses to methyl jasmonate (MeJA) and diethyldithiocarbamic acid (DIECA, an inhibitor of JA biosynthesis) treatments in wound yam tubers were investigated. The results showed that exogenous MeJA promoted the production of endogenous JA with increased gene expressions of lipoxygenase (LOX) and 12-oxo-phytodienoic acid reductase (OPR) in wound tubers. The activities and gene expressions of phenylalanine ammonialyase (PAL), cinnamic acid 4-hydroxylase (C4H) and 4-coumarate-CoA ligase (4CL) in wound tubers were pronouncedly enhanced by MeJA, along with increase of SPP monomers, especially, hydroxycinnamic acids (HAs). Meanwhile, MeJA increased the activities and gene expressions of peroxidase (POD), NADPH oxidase (NOX), polyamine oxidase (PAO), and the generation of hydrogen peroxide (H2O2), which were likely to be involved in the polymerization of SPP monomers resulting in SPP deposition. Conversely, inhibition of JA biosynthesis by DIECA reversed the positive impact of MeJA on wound healing process. The results indicate that rapid wound healing in Chinese yam tubers could be induced by MeJA via stimulating phenylpropanoid metabolism, POD activity and H2O2 generation involved in SPP deposition.