Different Alternation In DNA Methylation In Different Rice (Oryza Sativa L.) Genotypes Following Electrostatic Treatments

McClintock proposed the idea of large-scale genomic changes in response to unusual external stress. Recent studies have indicated that changes of gene expression can be couple with alteration in DNA methylation, which might play a role in help coping with the specific stress. Electrostatic field represents a"positive"stress to plants, whereby the treated plant opften show enhanced groth and development. It is unknown whether this physiological response by plants to electrostatic treatments are associated with alteration in cytosine methylation. In this study, five different genotypes of rice (Oryza sativa L.) were used to investigate the possible effects of electrostatic treatments on changes in DNA methylation. Various approaches, including MSAP (Methylation-sensitive fragment length polymorphism),Southern blotting, semi-quantitative and real-time RT-PCR were used to investigate possible changes in DNAmethylation and their association with alteration in gene expression.The MSAP results indicated that after electrostatic treatments, all five rice genotypes showed variation in DNA methylation patterns compared with their respective untreated controls , but with sharp difference in trend and extent of the changes. For example, Matsumae and Nipponbare showed contrast trends (hypo- and hyper-methlation respectively) in methylation changes after the electrostatic treatments, the three rice recombinant inbred lines showed—complicated methylation changes which did not accord with each other.Sequencing results of 35 isolated variant MSAP bands implicated that diverse functional sequences were involved which included those of various signaling pathways, stress-responsive genes and the mobile genetic elements (TEs). Further, we selected several stress-responsive cellular genes and TEs as probes and primers to perform Southern blot analysis and RT-PCR. The results showed that there were a general agrement between the treend of methylation alteration (hypomethylation) and changes in gene expression (upregulation) in Nipponbare. But incngrency between methylation alteration (largely hypermethylation) and changes in gene expression (mainly upregulation) was noted for Matsumae. These observations suggest that the electrostatic stress induced responces in DNA methylation alteration and changes in gene expression are genotype-dependent in rice. Finanly, we selected a subset of chromatin-related genes and analyzed their expression in the electrostatic field treated plants and their controls by real-time q-RT-PCR and found that significant changes in expression occurred fro several of the genes, implying that the DNA methylation alterations were likely related to chromatin alterartions.Taken together, this study has provided some novel information regarding the biological effects by electrostatic treatments in plants.