Study On Interaction And Epigenetic Inheritance Of Histone And DNA Methylaton

In eukaryote, genomic DNA is packaged in chromatin by twining with histone octamer. Chromatin can be covalently modified, such as histone modifications and DNA methylation. Epigenome, which is the combination of all chromatin modifications over a given genome, defines the gene expression profile of a particular type of cell or a cell response to a given inner/outer stimuli. Epigenome can be inherited to daughter cell or offsprings through mitosis and meiosis. Here, a chromatin modifier (histone demethylase) and a epigenetic phenomena are studied for the purpose of understanding the interaction and inheritance of chromatin modifications and their roles in gene expression regulation.Rice JMJ703protein, belonging to JumonjiC domain containing protein family, demethylates mono-, di-and trimethylation on methylated H3K4(H3K4me1/2/3). Crystal structure of this protein was resolved to get further insight into the demethylation activity and substrate recognition. Loss-of-function mutation of jmj'703results in semi-dwarf phenotype in rice. No significant difference of cell length is observed between wild type and mutant, which leads to the proposition that the rate of cell division is affected in jmj703mutant. Further analysis showed increased expression of cytokinin oxidase (CKX) genes in the absence of JMJ703. Chromatin immunoprecipitation revealed increased H3K4me3over CKX genes, which is in consistent with the enhanced expression of the genes. Taken togenther, JMJ703may limit the expression of CKX genes by demethylating H3K4me3to balance the hormone level in order to ensure normal stem elongation in rice. To investigate the roles of JMJ703in chromatin modification interaction and inheritance, DNA methylation of repeated sequences and retrotransposons were studied in jmj703plants, little change was observed. Nevertheless, overexpression of JMJ703affects DNA methylation of a gene by abolishing H3K4me3in genic region.In order to investigate reprogram and inheritance of chromatin modifications, genes specifically expressed in callus, termed as plant stem cell, were studied by searching public database, which leads to the emergence of a DNA methylation repressed gene, CXS (constant exclusion of silence). Cell dedifferentiation results in activation of CXS, which shows enrichment of H3K4me3, decrease of H3K27me3and low nucleosome occupation around transcription start site (TSS) simultaneously. DNA methylation inhibitor treatment experiment suggests that DNA demthylation is sufficient for activating CXS expression and H3K4me3enrichment. Active CXS expression and its chromatin modifications are memorized through generations. Overexpression of an H3K4me demethylase JMJ703results in CXS repression and DNA remethylation. JMJ703protein is found bound to CXS locus, suggesting that H3K4me3may promote CXS expression and protect DNA from remethylation during redifferentiation. In consistent with that, CXS expression shows a little increase in seedling of jmj703mutant. CXS expression is also abolished in an H3K27methyltransferase gene OsCLF overexpression plants and a chromatin remodelling factor chr729mutant. All repressed CXS regains DNA methylation and shows normal H3K4me3and H3K27me3compared to wild type plants. However, active CXS is detected in jmj703/chr729double mutant, suggesting that JMJ703mediate demthylation is essential for CXS repression, which is excluded by CHR729. Furthermore, CXS expression can be detected in callus of oxJM/703, OsCLF overexpression and chr729mutant and is not affected in jmj'703callus compared to wild type. These results suggest that JMJ703, OsCLF and CHR729protein may not function at callus stage, but during redifferentiation. Taken all, it is concluded that CXS is activated in callus, stem cell like in rice, due to the open environment of chromatin. The active state, including enriched H3K4me3and decreased H3K27me3, is maintained with help of CHR729protein, which protects CXS from JMJ703and OsCLF.