Study On The Relationship Between Tissue Culture Induced Rice Met1-2 Mutant Retrotransposon Tos17 Activity And Histone Modifications

Genetic and Epigenetic variation can be induced by plant tissue culture. Epigenetic variation showed DNA methylation and histone modification,etc. As an important way of epigenetic regulation, histone code greatly enriches the genetic information of genome in eukaryotes. Histone methylation and histone acetylation play important roles in maintaining genomic stability and regulation of gene expression. Epigenetic variation, such as DNA methylation, histone modification, chromatin remodeling does not happen alone, but work together to constitute the epigenetic regulation in the tissue culture process. In addition transposon can be induced to transpose by tissue culture, that has an important impact on the structure and function of plant genome. MET1-2 is the main methyltransferase responsible for maintenance of CG methylation in rice. Based on the current progress of the study in our laboratory, loss of function of MET1-2 will lead to genome-wide demethylation in CG locus. Usually most plant transposons stable silence.Tissue culture can induce transposon activation in calli of rice, including retrotransposon Tos17. In the case of loss of MET1-2 function in rice calli, retrotransposon Tos17 transposon more actively. However, in the plant genome, all kinds of epigenetic modification markers do not exist independently, but regulate the chromatin structure and gene expression together through interdependence and mutual recognition.In our study, we have five kinds of experimental materials, incuding the leaf of Japonica rice Nipponbare, the calli of Japonica rice Nipponbare, the calli of Os MET1-2+/+, the calli of Os MET1-2+/-,the calli of Os MET1-2-/-. By using whole genome sequencing technology to analysis the transposable elements(TEs) activation, we detected that 14 TE families were found in the calli of Os MET1-2-/-, including Tos17. The results from Southern blotting confirmed the results of whole genome sequencing. About 70% of the newly activated retrotransposon Tos17 insert into the body region of genome. By using chromatin immunoprecipitation technology to analysis the histone modification(H3K9me2、H3K27me3、H3K4me3 and H3K9ac2) on the retrotransposon Tos17, we detected that the modification level of H3K9me2 and H3K27me3 decreases in the calli of Os MET1-2-/-, but the modification level of H3K4me3 and H3K9ac2 increases in the calli of Os MET1-2-/-.This study demonstrated that there is some relationship between the activity of retrotransposon Tos17 and histone modification. Our results may lay the foundation for further studying on regulatory mechanism of epigenetic modification markers in the process of the transposon activation in rice.