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Assaf Zemach, M Yvonne Kim, Ping-Hung Hsieh, Devin Coleman-Derr, Leor Eshed-Williams, Ka Thao, Stacey L Harmer, Daniel Zilberman
Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
Cell. 2013 Mar 28;153(1):193-205. doi: 10.1016/j.cell.2013.02.033.
Nucleosome remodelers of the DDM1/Lsh family are required for DNA methylation of transposable elements, but the reason for this is unknown. How DDM1 interacts with other methylation pathways, such as small-RNA-directed DNA methylation (RdDM), which is thought to mediate plant asymmetric methylation through DRM enzymes, is also unclear. Here, we show that most asymmetric methylation is facilitated by DDM1 and mediated by the methyltransferase CMT2 separately from RdDM. We find that heterochromatic sequences preferentially require DDM1 for DNA methylation and that this preference depends on linker histone H1. RdDM is instead inhibited by heterochromatin and absolutely requires the nucleosome remodeler DRD1. Together, DDM1 and RdDM mediate nearly all transposon methylation and collaborate to repress transposition and regulate the methylation and expression of genes. Our results indicate that DDM1 provides DNA methyltransferases access to H1-containing heterochromatin to allow stable silencing of transposable elements in cooperation with the RdDM pathway.
DDM1/Lsh 家族的核小体重塑因子对于转座元件的 DNA 甲基化是必需的，但原因尚不清楚。DDM1 如何与其他甲基化途径相互作用，如小 RNA 指导的 DNA 甲基化 (RdDM)，后者被认为通过 DRM 酶介导植物不对称甲基化，目前也不清楚。在这里，我们表明，大多数不对称甲基化是由 DDM1 介导的，与 RdDM 途径分开，由甲基转移酶 CMT2 介导。我们发现，异染色质序列优先需要 DDM1 进行 DNA 甲基化，这种偏好取决于连接组蛋白 H1。RdDM 则被异染色质抑制，绝对需要核小体重塑因子 DRD1。总之，DDM1 和 RdDM 介导了几乎所有的转座子甲基化，并共同抑制转座和调节基因的甲基化和表达。我们的结果表明，DDM1 为 DNA 甲基转移酶提供了进入含有 H1 的异染色质的途径，以允许与 RdDM 途径合作，稳定沉默转座元件。
