Changes Of DNA Methvlation Pattern And Its Regulation On Gene Expression During Arabidopsis Leaf Senescence

Leaf senescence is the last stage of leaf growth and development,and was important to crop yield and quality.Leaf senescence is controlled by internal and external factors,forming a complex genetic and epigenetic control network.In this study,the whole genome methylation sequencing(WGBS)technique was used to analyze the methylation level and pattern of Arabidopsis leaves in four stages,and the candidate genes of DNA methylation involved in leaf senescence were screened out by combining the data of DNA methylation and gene expression.In order to find the enzyme that might involved in leaf senescence,The expression patterns of DNA methyltransferase and demethylase during Arabidopsis leaf senescence were analyzed,and the phenotypic of related mutants was observed.Elucidating the role of DNA methylation in leaf senescence.The main results of this study are as follows:(1)In this study,whole-genome bisulfite sequencing(WGBS)was used to profile the methylomes of Arabidopsis leaf senescence.Leaves at four developmental and senescence stages,namely YL(young leaf),NS(fully expanded young leaf),ES(early senescing leaf)and LS(late senescing leaf)were selected.The methylation level of CG sequence was found to be much higher than that of CHG and CHH.The number of sites of mCG was also higher than that of CHG and CHH,and the number of CG sites in hypermethylation was significantly decreased during leaf senescence.In addition,a total of 2714 differential methylation regions(DMRs)were detected through comparative methylome analysis,which were associated with 1383 differential methylation genes(DMGs).The number of genes in the CG contexts was much higher than that of the CHG and CHH,and the DMGs of the CG contexts tend to be demethylated during the senescence,while the CHG contexts tend to be hypermethylated.The results indicate that demethylation occurring in the CG sequence may play an important role in leaf senescence.(2)Correlation analysis between the data of DNA methylation and the gene expression,and found 116 genes showed correlation between DNA methylation and gene expression.Among them,75(64.7%)genes were negative correlation,41(35.3%)genes were positive correlation,and 40(34.5%)genes have DMR in their promoter regions,while 76(65.5%)genes have DMR in their gene body regions.Indicating that DNA methylation may negatively regulate the gene expression during leaf senescence,and DNA methylation in gene bodies might affect gene expression more effectively.In addition,most of these genes(58)showed methylation levels decreased and gene expression up-regulated,functional analysis analysis found that they participate in a number of biological processes,the candidate genes such as WRKY26,SAG24,MKK4,RD20 may play an important role during leaf senescence,these results suggest that DNA methylation is associated with the occurrence of leaf senescence..(3)The expression patterns of methyltransferase and demethylase in the process of leaf senescence were analyzed.It was found that the methyltransferase genes MET1 and CMT3 were down-regulated,while DML2 and DML3 were up-regulated.DML3 was significantly up-regulated in ES,and its mutants delayed leaf senescence,suggesting that demethylase DML3 may regulate leaf senescence by demethylating senescence-related genes.