Plant Cell∣清华大学戚益军教授发文揭示植物中RNA聚合酶的组装机理

2018年1月18日Plant Cell在线发表了题目为“A Role for MINIYO and QUATRE-QUART 2 in the Assembly of RNA Polymerases II, IV and V in Arabidopsis”的文章。

本文由清华大学生命科学学院植物生物学研究中心戚益军教授课题组完成。文章揭示了植物中RNA聚合酶的组装机理。

IYO和QQT2通过促进RNA聚合酶II，IV和V的装配，在RNA介导的DNA甲基化所需的24-nt siRNA和转录本的生物合成中起作用。

摘要：

RNA聚合酶IV和V（Pol IV和Pol V）是RNA介导的DNA甲基化（RdDM）产生非编码RNA所必需的。它们的亚基组成与Pol II类似。不过它们组装的机制和辅助因子在很大程度上还不清楚。在本研究中，我们鉴定了拟南芥中引起RdDM缺陷的IYO，QQT2和NRPB/D/E11等位基因的突变。我们发现Pol IV依赖的小干扰RNA（siRNA）和Pol V依赖的转录本在这些突变体中大大减少。在突变体iyo和qqt2中，Pol V的最大亚基NRPE1，不能与Pol V的其他亚基结合，暗示IYO和QQT2参与了Pol V的装配。此外，我们发现，在组装Pol V全酶之前，IYO和QQT2与NRPE3组件的结合是相互依赖的。最后，对于Pol II和Pol IV的组装，都是同样需要IYO和QQT2的。我们的研究结果揭示了IYO和QQT2是Pol II，Pol IV和Pol V组装的辅助因子，以及植物中RNA聚合酶的组装机理。

Abstract：

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 MINIYO (IYO), QUATRE-QUART 2 (QQT2) and NUCLEAR RNA POLYMERASE B11/D11/E11 (NRPB/D/E11) that cause defects in RdDM in Arabidopsis. We found that Pol IV-dependent small interfering RNAs (siRNAs) and Pol V-dependent trans were greatly reduced in the mutants. NRPE1, the largest subunit of Pol V, failed to associate with other Pol V subunits in the iyo and qqt2 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.