The Arabidopsis chromatin-modifying nuclear siRNA pathway involves a nucleolar RNA processing center
The Arabidopsis chromatin-modifying nuclear siRNA pathway involves a nucleolar RNA processing center
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DOI：
10.1016/j.cell.2006.05.031
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发表时间：
2006-07-14
期刊：
影响因子：
64.5
通讯作者：
Pikaard, Craig S.
中科院分区：
文献类型：
--
作者：
Pontes, Olga;Li, Carey Fei;Pikaard, Craig S.
在拟南芥中，小干扰 RNA (siRNA) 在涉及两种形式的核 RNA 聚合酶 IV（Pol IVa 和 Pol IVb）、RNA 依赖性 RNA 聚合酶 2 (RDR2)、DICER-LIKE 3 (DCL3)、ARGONAUTE4 (AGO4)、染色质重塑剂 DRD1 和 de新胞嘧啶甲基转移酶 DRM2。我们发现 RDR2、DCL3、AG04 和 NRPD1b（Pol IVb 的最大亚基）与核仁内的 siRNA 共定位。相比之下，Pol IVa 和 DRD1 位于核仁外部，并与内源重复基因座共定位。突变引起的通路蛋白丢失会导致下游蛋白错误定位，从而揭示它们的作用顺序。 Pol IVa 首先发挥作用，其定位依赖于 RNA，表明存在 RNA 模板。我们假设异染色质状态的维持涉及位点特异性 Pol IVa 转录，然后是 siRNA 的产生以及核仁加工中心内含有 AGO4 和 NRPD1b 的沉默复合物的组装。
In Arabidopsis thaliana, small interfering RNAs (siRNAs) direct cytosine methylation at endogenous DNA repeats in a pathway involving two forms of nuclear RNA polymerase IV (Pol IVa and Pol IVb), RNA-DEPENDENT RNA POLYMERASE 2 (RDR2), DICER-LIKE 3 (DCL3), ARGONAUTE4 (AGO4), the chromatin remodeler DRD1, and the de novo cytosine methyltransferase DRM2. We show that RDR2, DCL3, AG04, and NRPD1b (the largest subunit of Pol IVb) colocalize, with siRNAs within the nucleolus. By contrast, Pol IVa and DRD1 are external to the nucleolus and colocalize with endogenous repeat loci. Mutation-induced loss of pathway proteins causes downstream proteins to mislocalize, revealing their order of action. Pol IVa acts first, and its localization is RNA dependent, suggesting an RNA template. We hypothesize that maintenance of the heterochromatic state involves locus-specific Pol IVa transcription followed by siRNA production and assembly of AGO4- and NRPD1b-containing silencing complexes within nucleolar processing centers.