Research Of DNA Methylation Variation Across Embryo And Endosperm In Maize And Wheat

Epigenetic modification plays important roles in plant and animal development. Epigenetic modification include DNA methylation, histone methylation, and so on. DNA methylation can affect the transposable element(TE) silencing, gene imprinting and regulation of gene expression.(1) Through a genome-wide analysis, distinct DNA methylation level across maize embryo and endosperm was observed. The DNA methylation level of maize embryo was higher than that in endosperm. However, the endosperm chloroplast(Pt) genome was more methylated to compare with the embryo chloroplast genome. DNA methylation regions were identified and mapped to the corresponding chromosome regions. CG island(CGI) shore contained more DNA methylation regions than CGI in maize suggested that DNA methylation level was not positively correlated with Cp G density. The DNA methylation occurred more frequently in the promoter sequence and transcriptional termination region(TTR) than other regions of the genes. The result showed that TEs were more methylated in maize embryo than in endosperm. Maize embryo and endosperm exhibit distinct pattern/level of methylation. The most differentially methylated two regions between embryo and endosperm were High Cp G content promoters(HCPs) and high Cp G content TTRs(HCTTRs). Methylation distinction of mitochondria and chloroplast DNA were less than the nucleus DNA. Our results indicated that DNA methylation was associated with gene silence or activity in maize endosperm and embryo. Many genes involved in embryogenesis and seed development were found differentially methylated across embryo and endosperm. Ninteen endosperm-specific expressed imprinting genes were found hypomethylated in endosperm and were hypermethylated in embryo. The DNA methylation level of many genes associated with material accumulation in maize embryo was very diffrenet from in endosperm. The distinct of these genes’ DNA methylation level between embryo and endosperm was associated with the distinct of their expression level. The expression of a maize DME-like gene and MBD101 gene(MBD4 homolog) which direct bulk genome DNA demethylation were higher in endosperm than in embryo. The expression level of these genes may be associated with the distinct methylation level of maize embryo and endosperm.(2) The methylation of wheat granule bound starch synthase 1(GBSS1)gene and starch branching enzyme IIa(Sbe IIa) gene was analysed. We found that the higher DNA methylated level of GBSS1 promoter in wheat embyo repressed the expression of GBSS1 in embryo. The embryo-specific expression of Sbe IIa gene was not associated with the DNA methylation, but with the tissue specific promoter cis-elements.We constructed the pSbeIIa::GUS and pGBSS1::GUS constructs and transfered into tobacco by Agrobacterial mediated method. GUS expression could be detected in embryo of transgenic tobacco containing p Sbe IIa::GUS, but not in other tissues. The result is consist with that the Sbe IIa gene expression with a embryo-specifc manner in wheat. In transgenic tobacco containing GBSS1::GUS, GUS accumulation could be detected in the early stage endosperm but not in late stage endosperm or other tissues. In wheat, the GBSS1 gene promoter is endosperm-specific.The differential activity of GBSS1 gene promoter between tobacco(dicotyledon) and wheat(monocotyledon) could be associated with the distinct development pattern of their endosperm. The starch synthesis and accumulation present in wheat both during the early developmental stage and late developmental stage, which was different in tobacco endosperm.Our research showed that DNA methylation can regulate the distinct of many genes expression between embryo with endosperm in maize and wheat. So the DNA methylation plays a very important role in seed development.