Decrease in DNA methylation 1(DDM1) is required for the establishement of CHH islands in maize. Decrease in DNA methylation 1(DDM1) is required for the establishement of CHH islands in maize

DNA methylation plays a crucial role in suppressing mobilization of transposable elements and regulation of gene expression. A number of studies have indicated that DNA methylation pathways and patterns exhibit distinct properties in different species, including Arabidopsis, rice, and maize. Here, we characterized the function of DDM1 in regulating genome-wide DNA methylation in maize. Two homologs of ZmDDM1 are abundantly expressed in the embryo and their simultaneous disruption caused embryo lethality with abnormalities in cell proliferation from the early stage of kernel development. We establish that ZmDDM1 is critical for DNA methylation, at CHG sites, and to a lesser extent at CG sites, in heterochromatic regions, and unexpectedly, it is required for the formation of m CHH islands. In addition, ZmDDM1 is indispensable for the presence of 24-nt siRNA, suggesting its involvement in the RdDM pathway. Our results provide novel insight into the role of ZmDDM1 in regulating the formation of m CHH islands, via the RdDM pathway maize, suggesting that, in comparison to Arabidopsis, maize may have adopted distinct mechanisms for regulating m CHH. Overall design: Characterize the function of chromatin remodeling factor DDM1 on DNA methylation in zea mays

DNA甲基化（DNA methylation）在抑制转座因子（transposable elements）的转座与调控基因表达（gene expression）过程中发挥关键作用。多项研究表明，DNA甲基化通路与模式在不同物种中表现出迥异的特性，涵盖拟南芥（Arabidopsis）、水稻（rice）与玉米（maize）。本研究针对玉米中DDM1调控全基因组DNA甲基化的功能展开系统表征。ZmDDM1（Zea mays DDM1）的两个同源基因在胚胎中大量表达，同时敲除这两个基因会导致胚胎致死，并在籽粒发育早期即出现细胞增殖异常。本研究证实，ZmDDM1对于异染色质区域的CHG位点DNA甲基化至关重要，对CG位点的甲基化也存在一定程度的调控作用；意外的是，ZmDDM1也是mCHH岛形成所必需的。此外，ZmDDM1对于24-nt小干扰RNA（24-nucleotide small interfering RNA, siRNA）的积累不可或缺，这提示其参与了RNA指导的DNA甲基化（RNA-directed DNA methylation, RdDM）通路。本研究结果揭示了ZmDDM1通过RdDM通路调控mCHH岛形成的全新机制，表明相较于拟南芥，玉米可能演化出了独特的mCHH甲基化调控机制。
实验设计：表征染色质重塑因子DDM1对玉米（Zea mays）DNA甲基化的调控功能。