Functional Analysis Of Arabidopsis Melatonin Synthesis Gene SNAT In Salt Response

Soil salinization is a major problem that needs to be solved urgently,which affects crop growth,restricts agricultural development and threatens global food security.Exploring the mechanisms of plant responses to salt stress and mining salt tolerance genes is the focus of current research.Although great progress has been made in the exploration of the regulatory pathways and molecular mechanisms of plant salt tolerance response,it still needs to be further improved and supplemented.The mechanism of plant hormones and their synthesis in response to salt stress has not been thoroughly studied.As a trace hormone,melatonin has been paid more attention due to its efficient ability in reactive oxygen species scavenging.At present,the research on the improvement of plant salt tolerance by melatonin mainly focuses on the growth and physiological observation after exogenous melatonin treatment.There is a lack of relevant research on the effect of endogenous melatonin synthesis in plants salt tolerance.5-hydroxytryptamine-N-acetyltransferase(SNAT)is an important synthetic enzyme in the melatonin biosynthesis pathway.However,little is known about the mechanism of SNAT in regulating plant salt tolerance.In this study,we used the knockout mutant of melatonin synthesis gene SNAT as material,performing melatonin content,phenotype,physiological monitoring and transcriptome sequencing analysis to explore the function of endogenous melatonin and its synthesis gene SNAT in salt response.The main results are as follows:(1)The analysis of endogenous melatonin showed that melatonin synthesis was increased in Arabidopsis plants under salt stress,and the expression of genes encoding melatonin synthesis enzymes was significantly up-regulated,indicating that trace hormone melatonin was involved in salt stress response.Based on this,loss-of-function mutants of melatonin synthesis genes SNAT1 and SNAT2 were obtained and the melatonin content was measured.The results showed that the endogenous melatonin of SNAT1 and SNAT2 double mutants was significantly reduced,which significantly affected the endogenous synthesis of melatonin.(2)Compared with the wild type,the snat1snat2 double mutant showed slightly yellow leaves,shorter root length,reduced biomass,and significantly decreased germination rate,greening rate,and survival rate.Physiological monitoring results showed that relative water content,Na~+/K~+ratio,ROS accumulation,and leaf photoprotection of snat1snat2 double mutant all were disturbed under salt stress,demonstrating that the melatonin synthesis gene SNAT plays an important role in plant response to salt stress.(3)In order to explore the possible physiological and metabolic pathways of salt tolerance affected by endogenous melatonin,transcriptome sequencing analysis was performed for the wild type and snat1snat2 double mutant under salt treatment for 72 h,and it was found that the expression of related genes involved in multiple biological pathways changed significantly after SNAT defect.Functional enrichment analysis of salt-responsive genes affected by SNAT showed that most of the genes were closely related to the synthesis of auxin and several signaling pathways.The possible regulation of auxin pathway by SNAT and melatonin was demonstrated by the measurement of auxin content in snat1snat2 and by the recovery of the salt-sensitive growth phenotype of snat1snat2 after exogenous NAA,IAA treatment.In summary,this study explored the biological function of melatonin synthesis gene SNAT in salt response,and elucidated the physiological function and potential mechanism of endogenous melatonin in plant response to salt stress,which provided theoretical basis for further understanding the molecular mechanism of trace hormones in regulating plant salt tolerance.