Department of Genetics, University of Georgia, Athens, GA 30602, USA.
Department of Genetics, University of Georgia, Athens, GA 30602, USA.
Mol Plant. 2018 Mar 5;11(3):381-387. doi: 10.1016/j.molp.2017.10.002. Epub 2017 Oct 13.
Plants encode a diverse repertoire of DNA methyltransferases that have specialized to target cytosines for methylation in specific sequence contexts. These include the de novo methyltransferase, DOMAINS REARRANGED METHYLTRANSFERASE 2 (DRM2), which methylates cytosines in all sequence contexts through an RNA-guided process, the CHROMOMETHYLASES (CMTs), which methylate CHH and CHG cytosines (where H is A, T, or C), and METHYLTRANSFERASE 1 (MET1), which maintains methylation of symmetrical CG contexts. In this review, we discuss the sequence specificities and targeting of each of these pathways. In particular, we highlight recent studies that indicate CMTs preferentially target CWG or CWA/CAW motifs (where W is A or T), and discuss how self-reinforcing feedback loops between DNA methyltransferases and histone modifications characteristic of heterochromatin specify targeting. Finally, the initiating events that lead to gene body methylation are discussed as a model illustrating how interdependent targeting of different silencing pathways can potentiate the establishment of off-target epialleles.
植物编码了多种 DNA 甲基转移酶，这些酶具有特异性，能够在特定的序列背景下靶向胞嘧啶进行甲基化。其中包括从头甲基转移酶 DOMAINS REARRANGED METHYLTRANSFERASE 2（DRM2），它通过 RNA 指导的过程甲基化所有序列背景中的胞嘧啶，以及 CHROMOMETHYLASES（CMTs），它甲基化 CHH 和 CHG 胞嘧啶（其中 H 是 A、T 或 C），以及 METHYLTRANSFERASE 1（MET1），它维持 CG 对称序列的甲基化。在这篇综述中，我们讨论了这些途径的每个途径的序列特异性和靶向性。特别是，我们强调了最近的研究表明 CMTs 优先靶向 CWG 或 CWA/CAW 基序（其中 W 是 A 或 T），并讨论了 DNA 甲基转移酶和组蛋白修饰之间的自我强化反馈环如何特征性地指定异染色质的靶向。最后，讨论了导致基因体甲基化的起始事件，作为一个模型说明了不同沉默途径的相互依赖的靶向如何增强非靶标表观等位基因的建立。
