Effects On DNA Methylation In Cucumber Seedling Under Heat Stress

High temperature had become one of stress factors during its stage of plant growth and development. The loss caused by High temperature has become the main hamper factor of cucumber production in summer cultivation or protected cultivation. Under the heat stress,the yield and resistance of cucumber were frequently decreasing, and quantities of malformation fruit was aising.At present, screening methods and criterion of heat resistence had been mainly carried out in cucumber. Studies of molecular markers and heredity to heat resistence had been made progresses. With the development of epigenetics, the molecular regulation mechanism of plant resistence to heat stress had a broader perspective. Under biotic or abiotic stress, genomic DNA methylation possess the gene expression ability of the plant response to stress. DNA methylation could be passed on to offsprings, and the stability and plasticity of the genome would be increased. DNA methylation is very important in genetic expression. the flowering process of plants and the formation and germination of seeds. Genomic DNA methylation was found to be associated with the heat resistance of plants. In order to reveal the molecular mechanism of cucumber resistant to heat stress, guide the practice of cucumber breeding, cucumber heat resistant cultivar 631 and heat sensitive cultivar L18 were used in this experiment. When two leaves of seedlings were appeared, the seedlings were treated under 38℃ for two hours. The DNA methylation of cucumber seedling were detected using MSAP(methylation sensitive amplification polymorphism) technique. The experimental results were as follows:(1)The methylation level of heat sensitive variety L18 genomic is lower than that of heat resistant varietiey 631 after heat treatment.(2)Twelve kinds of methylation polymorphisms were detected, and Twelve kinds were classified two types that were methylation and demethylation.The rate of total methylation was 26.90% and rate of total demethylation 22.58%.(3)The change rate of genomic DNA methylation polymorphisms in heat resistant material 631 was 30.26% and 19.22% in heat-sensitive material L18.(4)Fifty four fragments of specific methylation were cloned and sequenced. The position of forty seven fragments were located in cucumber chromosome, and the sequences of most specific fragments belong to part of coding domain sequence.(5)Changes of thirteen methylation sites in heat resistance cucumber 631 were demethy lation after heat stress, and opposite in heat-sensitive cucumber L18.( 6) Four specific fragments were candidates in studies of cucumber heat stress in future,they are UDP- glycosyl- transferase 85A3、pentatricopeptide repeat-containing protein、CBL-interacting protein kinase,CIPK6 and E3 ubiquitin ligase.