Effect Of Powdery Mildew On DNA Methylation And Transcriptome For Leaves Of Melon Seedlings

Melon(Cucumis melo L.)is a Cucurbitaceae Cucumis plant,and it is enjoyed by consumers because of its special aroma,sweet taste and rich nutrition.Powdery mildew is serious diseases that affect the production and economic benefits of melon.The genes response of plants was usually changed significantly with the interaction of plant and pathogen,and plants can form a series of defense through regulating enzyme expression and physiological metabolism.At present,the study of powdery mildew affecting DNA methylation and gene expression network is short of systematic investigation.In this study,'yangjiaomi' melon was used as plant material,the effect of powdery mildew on DNA methylation and gene expression were investigated using whole genome methylome and transcriptome sequencing approach,which provides a basic for understanding the molecular mechanism of melon responsive to powdery mildew.The main results are shown as follows:1.The results of genome DNA methylation was estimated by the requirements and quality of sequencing.The number of DMRs was identified by the three forms of CpG,CHG and CHH,which were respectively 8,047,4,872 and 6,686.The DNA methylation level of melon in the leaves was significantly increased by powdery mildew infection.The degree of different hypermethylated region was higher than that of different hypomethylated region.Under different modification,the distribution of DMR in the genomic functional region is different.2.Transcriptome sequencing has qualified quality,comprehensive data and high coverage.We identified 4,808 differentially expressed genes,of which 2,315 was up-regulated,and 2,493 was down-regulated.The differential analysis showed that the down-regulated genes induced by powdery mildew were mostly concentrated on the plant growth process,while the up-regulated genes focused on the disease resistance process.3.Combined analysis of whole genome DNA methylation sequencing and transcriptome sequencing showed that 1,520 different expressed genes with differentiated hypermethylated regions and 1,057 different expressed genes with differentiated hypomethylated regions were identified in this study.And 2,134 unique genes were identified among them.These different genes are mainly involved in the basic processes of plant metabolism,cell growth and catalysis according to the GO enrichment analysis.Hypermethylated different expressed genes are more than hypomethylated different expressed genes.The relationship between DNA methylation and gene expression is complex.In these results,we analyzed 70 differentially expressed genes with DMR.We found that most of the genes' methylation levels were elevated,and gene expression levels were reduced;or their methylation levels were reduced,and gene expression levels were elevated.This is consistent with the biological relationship between DNA methylation and gene expression.4.When melon seedlings was infected with powdery mildew,the expression levels of two ribulose-1,5-diphosphate carboxylase / oxygenase gene were down-regulated;and the expression levels of 22 genes in chlorophyll metabolism were significantly changed,among which 18 genes were down-regulated.Additionally the expression levels of 51 genes in photosynthesis were significantly changed,of which 50 genes were down-regulated.These results suggest that the photosynthesis and chlorophyll synthesis are inhibited by powdery mildew,affecting the supply of nutrients,resulting in plant growth inhibition.When melon was infected by powdery mildew,chitinase,phenylalanine ammonia lyase,4-coumaric acid-coenzyme A ligase,polyphenol oxidase,peroxidase,ethylene response transcription factor and WRKY transcription factor,were significantly increased.These results indicate that,after infected with powdery mildew,the expression levels of photosynthetic genes in melon seedlings were down-regulated and the expression levels of resistance-related genes were up-regulated.Down-regulated different expressed genes were more than up-regulated by different expressed genes,and this is consistent with the degree of different hypermethylated region was much higher than that of different hypomethylated region.