The Molecular Mechanism Of Exogenous Melatonin In Promoting The Germination Of Maize(Zea Mays L.)Seeds Under Salt Stress

Salt stress is one of the important limiting factors that reduce crop yield.So it is an important way to improve crop yield by spraying exogenous substances to alleviate the salt stress of crops.Melatonin,also known as pineal gland,is a small molecule of indole that is widely found in organisms.It has been reported that the exogenous melatonin plays a vital role in improving the abiotic resistance of plants to drought,heat,cold and salt.However,the molecular mechanism of exogenous melatonin in promoting the germination of maize seeds under salt stress has never reported.In this study,maize inbred line B73 seeds were used as materials.The 100mmol/L NaCl and lO?mol/L melatonin were selected as salt stress condition and melatonin pretreatment codition.We set up three experimental treatments including control,salt stress and salt stress with melatonin pretreatment,respectively.The results showed that under the condition of melatonin pretreatment can significantly increase maize seed germination rate under salt stress.To further elucidate the molecular mechanism of exogenous melatonin in promoting maize seed germination under salt stress,the secondary metabolites and physiological and biochemical indexes related to seed germination were measured in three treatments.The primary metabolites of maize germinated seeds were determined based on metabolomics and transcriptome and miRNA were determined based on RNA-seq.The results showed that:(1)under salt stress,by melatonin pretreatment,the content of peroxidase(POD),hydrogen peroxide(CAT),superoxide dismutase(SOD),hydroxyl free radical clearance,a-amylase activity,p-amylase activity,gibberellic acid(GA3)and Indole Acetic Acid(IAA)content in germinated seeds were enhanced significantly;whereas the hydrogen peroxide(H2O2),starch content,plant soluble sugar content and isocitrate lyase(ICL)were reduced significantly.(2)By metabolitics analysis,142 primary metabolites were found difference between three treatments,where 102 differential metabolities were found between salt stress with melatonin pretreatment and salt stress.And the primary metabolites associated with the content of POD,antioxidant capacity and salicylic acid synthesis were significantly improved through the treatment of melatonin.(3)Based on the analysis of transcriptome,1061 differentially expressed genes were found between salt stress with melatonin pretreatment and salt stress,where 568 genes were up-regulated expression and 493 genes were down-regulated expression.These genes associated with metabolites-regulated pathway,transcription regulation and energy metabolism regulations,which were mainly involved in plant immune system,stress resistance and oxidation-reduction reactions.(4)By the miRNA analysis,83 miRNA were found difference among three treatments,where 69 miRNA were annotated 1027 target genes.And 15 target genes were found as differential expression gene between melatonin pretreatment and salt stress.Based on the multiomics methods,we found the pretreatment of exogenous melatonin could mediate transcription regulation and miRNA transcription regulation to improve seed antioxidant capacity under salt stress conditions,thus to increase the maize seeds germination under salt stress.The results of this study are of great theoretical significance to elucidate the molecular mechanism of exogenous melaton in promoting seed germination under salt stress,and will be helpful to alleviate the effects of maize on salt stress.