Department of Plant and Microbial Biology, University of California Berkeley, Berkeley, California, United States of America.
PLoS Genet. 2009 Nov;5(11):e1000706. doi: 10.1371/journal.pgen.1000706. Epub 2009 Nov 20.
Mutations affecting the heritable maintenance of epigenetic states in maize identify multiple small RNA biogenesis factors including NRPD1, the largest subunit of the presumed maize Pol IV holoenzyme. Here we show that mutations defining the required to maintain repression7 locus identify a second RNA polymerase subunit related to Arabidopsis NRPD2a, the sole second largest subunit shared between Arabidopsis Pol IV and Pol V. A phylogenetic analysis shows that, in contrast to representative eudicots, grasses have retained duplicate loci capable of producing functional NRPD2-like proteins, which is indicative of increased RNA polymerase diversity in grasses relative to eudicots. Together with comparisons of rmr7 mutant plant phenotypes and their effects on the maintenance of epigenetic states with parallel analyses of NRPD1 defects, our results imply that maize utilizes multiple functional NRPD2-like proteins. Despite the observation that RMR7/NRPD2, like NRPD1, is required for the accumulation of most siRNAs, our data indicate that different Pol IV isoforms play distinct roles in the maintenance of meiotically-heritable epigenetic information in the grasses.
影响玉米中表观遗传状态可遗传维持的突变鉴定了多个小 RNA 生物发生因子，包括假定的玉米 Pol IV 全酶的最大亚基 NRPD1。在这里，我们表明，定义维持抑制 7 座必需的突变鉴定了与拟南芥 NRPD2a 相关的第二个 RNA 聚合酶亚基，这是拟南芥 Pol IV 和 Pol V 之间唯一共享的第二个最大亚基。系统发育分析表明，与代表性的真双子叶植物相比，禾本科植物保留了能够产生功能性 NRPD2 样蛋白的重复基因座，这表明禾本科植物的 RNA 聚合酶多样性相对于真双子叶植物增加。与 rmr7 突变体植物表型及其对表观遗传状态维持的影响的比较，以及对 NRPD1 缺陷的平行分析表明，玉米利用多种功能性 NRPD2 样蛋白。尽管观察到 RMR7/NRPD2 与 NRPD1 一样，是大多数 siRNA 积累所必需的，但我们的数据表明，不同的 Pol IV 同工酶在禾本科植物中维持减数分裂可遗传的表观遗传信息方面发挥着不同的作用。
