Agricultural Biotechnology Center, Plant Biology Institute, PO Box 411, H-2101 Gödöllõ, Hungary.
Plant J. 2010 May;62(3):463-72. doi: 10.1111/j.1365-313X.2010.04163.x. Epub 2010 Feb 1.
RNA silencing plays an important role in plants in defence against viruses. To overcome this defence, plant viruses encode suppressors of RNA silencing. The most common mode of silencing suppression is sequestration of double-stranded RNAs involved in the antiviral silencing pathways. Viral suppressors can also overcome silencing responses through protein-protein interaction. The poleroviral P0 silencing suppressor protein targets ARGONAUTE (AGO) proteins for degradation. AGO proteins are the core component of the RNA-induced silencing complex (RISC). We found that P0 does not interfere with the slicer activity of pre-programmed siRNA/miRNA containing AGO1, but prevents de novo formation of siRNA/miRNA containing AGO1. We show that the AGO1 protein is part of a high-molecular-weight complex, suggesting the existence of a multi-protein RISC in plants. We propose that P0 prevents RISC assembly by interacting with one of its protein components, thus inhibiting formation of siRNA/miRNA-RISC, and ultimately leading to AGO1 degradation. Our findings also suggest that siRNAs enhance the stability of co-expressed AGO1 in both the presence and absence of P0.
RNA 沉默在植物抗病毒防御中起着重要作用。为了克服这种防御，植物病毒编码 RNA 沉默的抑制剂。沉默抑制最常见的模式是将参与抗病毒沉默途径的双链 RNA 隔离。病毒抑制剂还可以通过蛋白-蛋白相互作用来克服沉默反应。多粒病毒 P0 沉默抑制蛋白将 ARGONAUTE（AGO）蛋白靶向降解。AGO 蛋白是 RNA 诱导沉默复合物（RISC）的核心组成部分。我们发现 P0 不干扰含 AGO1 的预编程 siRNA/miRNA 的切割活性，但可防止含 AGO1 的 siRNA/miRNA 的从头形成。我们表明 AGO1 蛋白是高分子量复合物的一部分，这表明植物中存在多蛋白 RISC。我们提出，P0 通过与其蛋白成分之一相互作用来阻止 RISC 组装，从而抑制 siRNA/miRNA-RISC 的形成，并最终导致 AGO1 降解。我们的研究结果还表明，siRNA 增强了共表达 AGO1 在 P0 存在和不存在情况下的稳定性。
