Integration of the Metabolome and Transcriptome Reveals Diurnal Variability in the Effects of Melatonin on Salt Tolerance in Maize Seedlings

Salt hazard is one of the major environmental stresses that seriously threaten world food security. Although melatonin has been proven to improve stress tolerance in plants, the metabolic changes and gene transcription affected by melatonin (MT) under salt stress remain uncertain, especially in maize. In the present study, we investigated the differences in the diurnal metabolism and transcription of maize seedlings to reveal the MT-mediated changes in diurnal metabolism in response to salt stress. Transcriptome analysis identified melatonin crosstalk with other hormones affecting their signal transduction pathways. The transcriptome and metabolome co-analysis revealed that MT maintained osmotic potential and regulated energy supply by regulating sucrose and starch metabolism. In addition, the regulatory network showed that MT and its metabolites were significantly correlated with a series of stress and hormone-related transcription factor (TF) genes, such as JAZ3-1, JAZ9, WRKY28, and ERF020. Taken together, our results indicated that MT alleviated salt stress-induced damage, influenced diurnal metabolic changes in maize under salt stress, and crosstalk with other endogenous hormones to improve salt tolerance in maize.