Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
Graduate Program, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100730, China.
Plant Cell. 2018 Feb;30(2):466-480. doi: 10.1105/tpc.17.00380. Epub 2018 Jan 18.
RNA polymerases IV and V (Pol IV and Pol V) are required for the generation of noncoding RNAs in RNA-directed DNA methylation (RdDM). Their subunit compositions resemble that of Pol II. The mechanism and accessory factors involved in their assembly remain largely unknown. In this study, we identified mutant alleles of (), (), and () that cause defects in RdDM in We found that Pol IV-dependent small interfering RNAs and Pol V-dependent transcripts were greatly reduced in the mutants. NRPE1, the largest subunit of Pol V, failed to associate with other Pol V subunits in the and mutants, suggesting the involvement of IYO and QQT2 in Pol V assembly. In addition, we found that IYO and QQT2 were mutually dependent for their association with the NRPE3 subassembly prior to the assembly of Pol V holoenzyme. Finally, we show that IYO and QQT2 are similarly required for the assembly of Pol II and Pol IV. Our findings reveal IYO and QQT2 as cofactors for the assembly of Pol II, Pol IV, and Pol V and provide mechanistic insights into how RNA polymerases are assembled in plants.
RNA 聚合酶 IV 和 V（Pol IV 和 Pol V）是 RNA 指导的 DNA 甲基化（RdDM）中非编码 RNA 产生所必需的。它们的亚基组成类似于 Pol II。它们组装所涉及的机制和辅助因子在很大程度上仍然未知。在这项研究中，我们鉴定了突变等位基因（）、（）和（），这些等位基因在中导致 RdDM 缺陷。我们发现，突变体中 Pol IV 依赖的小干扰 RNA 和 Pol V 依赖的转录本大大减少。Pol V 的最大亚基 NRPE1 未能与和中的其他 Pol V 亚基结合，表明 IYO 和 QQT2 参与了 Pol V 的组装。此外，我们发现 IYO 和 QQT2 在 Pol V 全酶组装之前相互依赖与 NRPE3 亚基组装。最后，我们表明 IYO 和 QQT2 对于 Pol II 和 Pol IV 的组装同样是必需的。我们的发现揭示了 IYO 和 QQT2 作为 Pol II、Pol IV 和 Pol V 组装的辅助因子，并为 RNA 聚合酶在植物中如何组装提供了机制上的见解。
