Institut de Biologie Moléculaire des Plantes, Centre National de la Recherche Scientifique, Unité Propre de Recherche 2357, Conventionné avec l'Université de Strasbourg, 67084 Strasbourg, France.
Proc Natl Acad Sci U S A. 2012 Sep 25;109(39):15942-6. doi: 10.1073/pnas.1209487109. Epub 2012 Sep 10.
Posttranscriptional gene silencing (PTGS) mediated by siRNAs is an evolutionarily conserved antiviral defense mechanism in higher plants and invertebrates. In this mechanism, viral-derived siRNAs are incorporated into the RNA-induced silencing complex (RISC) to guide degradation of the corresponding viral RNAs. In Arabidopsis, a key component of RISC is ARGONAUTE1 (AGO1), which not only binds to siRNAs but also carries the RNA slicer activity. At present little is known about posttranslational mechanisms regulating AGO1 turnover. Here we report that the viral suppressor of RNA silencing protein P0 triggers AGO1 degradation by the autophagy pathway. Using a P0-inducible transgenic line, we observed that AGO1 degradation is blocked by inhibition of autophagy. The engineering of a functional AGO1 fluorescent reporter protein further indicated that AGO1 colocalizes with autophagy-related (ATG) protein 8a (ATG8a) positive bodies when degradation is impaired. Moreover, this pathway also degrades AGO1 in a nonviral context, especially when the production of miRNAs is impaired. Our results demonstrate that a selective process such as ubiquitylation can lead to the degradation of a key regulatory protein such as AGO1 by a degradation process generally believed to be unspecific. We anticipate that this mechanism will not only lead to degradation of AGO1 but also of its associated proteins and eventually small RNAs.
小 RNA 介导的转录后基因沉默 (PTGS) 是高等植物和无脊椎动物中一种保守的抗病毒防御机制。在这个机制中，病毒衍生的 siRNA 被整合到 RNA 诱导沉默复合物 (RISC) 中，以指导相应的病毒 RNA 的降解。在拟南芥中，RISC 的一个关键组成部分是 ARGONAUTE1 (AGO1)，它不仅与 siRNA 结合，还具有 RNA 切割活性。目前，关于调节 AGO1 周转的翻译后机制知之甚少。在这里，我们报道病毒沉默蛋白 P0 通过自噬途径触发 AGO1 的降解。利用 P0 诱导的转基因系，我们观察到自噬的抑制会阻断 AGO1 的降解。对功能性 AGO1 荧光报告蛋白的工程改造进一步表明，当降解受到干扰时，AGO1 与自噬相关 (ATG) 蛋白 8a (ATG8a) 阳性体共定位。此外，该途径还在非病毒环境中降解 AGO1，尤其是在 miRNA 产生受到损害时。我们的结果表明，泛素化等选择性过程可以导致关键调节蛋白如 AGO1 的降解，而这种降解过程通常被认为是非特异性的。我们预计，这种机制不仅会导致 AGO1 的降解，还会导致其相关蛋白和最终的小 RNA 的降解。
