Exogenous methyl jasmonate promotes the biosynthesis of endogenous melatonin in mustard sprouts

The present study investigated the effects regulating melatonin (MT) biosynthesis under methyl jasmonate (MeJA) treatment in mustard sprouts. The results revealed that MeJA significantly increased the MT content in the sprouts to 11.43 times that of the control. However, MeJA treatment had an inhibitory effect on growth. Tryptophan decarboxylase and tryptamine 5-hydroxylase gene expression were significantly induced by MeJA. Moreover, 156 differential abundance proteins (DAPs) were detected in 4-day-old sprouts using quantitative proteomic methods. These DAPs were divided into 13 functional groups, and the vast majority of DAPs involved in defense/stress, energy, signal transduction, and secondary metabolism increased. MeJA treatment significantly enriched 15 pathways, including glutathione metabolism, biosynthesis of secondary metabolites, and tryptophan metabolism. In particular, the abundance of three DAPs (myrosinase 1, cytosolic sulfotransferase 16, and glutamate-glyoxylate aminotransferase 2) in the tryptophan metabolism pathway, a substrate for MT biosynthesis, increased significantly. In summary, MeJA induces endogenous MT biosynthesis in mustard sprouts by promoting the genes expression of MT synthetase and increasing the abundance of tryptophan-related proteins.