Exogenous melatonin promotes rice seed germination under salinity through regulating antioxidants and metabolic homeostasis

Abstract Background Melatonin plays important roles in multiple plant developmental processes and stress responses. However, little is known about the role and putative mechanism of exogenous melatonin in regulating rice seed germination under salt stress. Main Body Here, we revealed that the exogenous application of melatonin can significantly promote rice seed germination under salinity. Its putative molecular mechanisms are further investigated through metabolomic and transcriptomic analyses. The results revealed that the phytohormone concentrations in germinating seeds are reprogrammed, the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) are enhanced, and the total antioxidant capacity under salinity is activated by exogenous melatonin. In addition, rice seeds pre-treated with melatonin exhibit higher concentrations of glycosides than non-treated seeds under salinity. Furthermore, exogenous melatonin alleviates the accumulation of fatty acids under salinity. Genome-wide transcriptomic profiling is used to identify 7160 transcripts which are differentially expressed under salt (NaCl), salt + melatonin (MT100), and control treatments. Pathway and GO enrichment analyses reveal that the genes involved in the response to oxidative stress, hormone metabolism, heme building, mitochondrion, and tricarboxylic acid transformation are altered after melatonin pre-treatment under salinity. Conclusion This study provides evidence for exogenous melatonin increasing rice seed germination under salt stress, mainly through the activation of antioxidants and modulation of metabolic homeostasis.