Zheng Qi, Rowley M Jordan, Böhmdorfer Gudrun, Sandhu Davinder, Gregory Brian D, Wierzbicki Andrzej T
Department of Biology, Penn Genomes Frontier Institute, University of Pennsylvania, Philadelphia, PA 19104, USA.
Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI 48109 , USA.
Plant J. 2013 Jan;73(2):179-89. doi: 10.1111/tpj.12034. Epub 2012 Nov 9.
Transcriptional gene silencing controls transposons and other repetitive elements through RNA-directed DNA methylation (RdDM) and heterochromatin formation. A key component of the Arabidopsis RdDM pathway is ARGONAUTE4 (AGO4), which associates with siRNAs to mediate DNA methylation. Here, we show that AGO4 preferentially targets transposable elements embedded within promoters of protein-coding genes. This pattern of AGO4 binding cannot be simply explained by the sequences of AGO4-bound siRNAs; instead, AGO4 binding to specific gene promoters is also mediated by long non-coding RNAs (lncRNAs) produced by RNA polymerase V. lncRNA-mediated AGO4 binding to gene promoters directs asymmetric DNA methylation to these genomic regions and is involved in regulating the expression of targeted genes. Finally, AGO4 binding overlaps sites of DNA methylation affected by the biotic stress response. Based on these findings, we propose that the targets of AGO4-directed RdDM are regulatory units responsible for controlling gene expression under specific environmental conditions.
转录基因沉默通过RNA介导的DNA甲基化（RdDM）和异染色质形成来控制转座子和其他重复元件。拟南芥RdDM途径的一个关键组分是AGO4，它与小干扰RNA（siRNA）结合以介导DNA甲基化。在这里，我们表明AGO4优先靶向嵌入在蛋白质编码基因启动子内的转座元件。AGO4这种结合模式不能简单地由AGO4结合的siRNA的序列来解释；相反，AGO4与特定基因启动子的结合也由RNA聚合酶V产生的长链非编码RNA（lncRNA）介导。lncRNA介导的AGO4与基因启动子的结合将不对称DNA甲基化导向这些基因组区域，并参与调控靶向基因的表达。最后，AGO4的结合与受生物胁迫反应影响的DNA甲基化位点重叠。基于这些发现，我们提出AGO4介导的RdDM的靶标是负责在特定环境条件下控制基因表达的调控单元。
