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RNA-directed DNA methylation mediated by DRD1 and Pol IVb: A versatile pathway for transcriptional gene silencing in plants

机译:由DRD1和Pol IVb介导的RNA定向的DNA甲基化:植物转录基因沉默的通用途径

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摘要

RNA-directed DNA methylation, which is one of several RNAi-mediated pathways in the nucleus, has been highly elaborated in the plant kingdom. RNA-directed DNA methylation requires for the most part conventional DNA methyltransferases, histone modifying enzymes and RNAi proteins; however, several novel, plant-specific proteins that are essential for this process have been identified recently. DRD1 (defective in RNA-directed DNA methylation) is a putative SWI2/SNF2-like chromatin remodelling protein; DRD2 and DRD3 (renamed NRPD2a and NRPD1b, respectively) are subunits of Pol IVb, a putative RNA polymerase found only in plants. Interestingly, DRD1 and Pol IVb appear to be required not only for RNA-directed de novo methylation, but also for full erasure of methylation when the RNA trigger is withdrawn. These proteins thus have the potential to facilitate dynamic regulation of DNA methylation. Prominent targets of RNA-directed DNA methylation in the Arabidopsis thaliana genome include retrotransposon long terminal repeats (LTRs), which have bidirectional promoter/enhancer activities, and other types of intergenic transposons and repeats. Intergenic solitary LTRs that are targeted for reversible methylation by the DRD1/Pol IVb pathway can potentially act as switches or rheostats for neighboring plant genes. The resulting alterations in gene expression patterns may promote physiological flexibility and adaptation to the environment.
机译:RNA定向的DNA甲基化是细胞核中几种RNAi介导的途径之一,在植物界已被高度阐述。 RNA指导的DNA甲基化在大多数情况下需要常规的DNA甲基转移酶,组蛋白修饰酶和RNAi蛋白。然而,最近已鉴定出对该过程必不可少的几种新颖的植物特异性蛋白质。 DRD1(RNA定向DNA甲基化缺陷)是一种假定的SWI2 / SNF2样染色质重塑蛋白。 DRD2和DRD3(分别更名为NRPD2a和NRPD1b)是Pol IVb的亚基,Pol IVb是仅在植物中发现的推定RNA聚合酶。有趣的是,DRD1和Pol IVb似乎不仅需要进行RNA定向的从头甲基化,而且在撤消RNA触发物时也需要完全擦除甲基化。因此,这些蛋白质具有促进DNA甲基化动态调节的潜力。拟南芥基因组中RNA定向DNA甲基化的主要目标包括反转录转座子长末端重复序列(LTR),其具有双向启动子/增强子活性,以及​​其他类型的基因间转座子和重复序列。靶向DRD1 / Pol IVb途径可逆甲基化的基因间孤立LTRs可能充当邻近植物基因的开关或变阻器。基因表达模式的改变可能会促进生理适应性和对环境的适应。

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