Douet Julien, Tutois Sylvie, Tourmente Sylvette
CNRS, UMR 6247 GReD, Clermont Université, INSERM U931, Aubière, France.
PLoS Genet. 2009 Oct;5(10):e1000690. doi: 10.1371/journal.pgen.1000690. Epub 2009 Oct 16.
The plant-specific RNA polymerases Pol IV and Pol V are essential to RNA-directed DNA methylation (RdDM), which also requires activities from RDR2 (RNA-Dependent RNA Polymerase 2), DCL3 (Dicer-Like 3), AGO4 (Argonaute), and DRM2 (Domains Rearranged Methyltransferase 2). RdDM is dedicated to the methylation of target sequences which include transposable elements, regulatory regions of several protein-coding genes, and 5S rRNA-encoding DNA (rDNA) arrays. In this paper, we have studied the expression of the 5S-210 transcript, a marker of silencing release at 5S RNA genes, to show a differential impact of RNA polymerases IV and V on 5S rDNA arrays during early development of the plant. Using a combination of molecular and cytological assays, we show that Pol IV, RDR2, DRM2, and Pol V, actors of the RdDM, are required to maintain a transcriptional silencing of 5S RNA genes at chromosomes 4 and 5. Moreover, we have shown a derepression associated to chromatin decondensation specific to the 5S array from chromosome 4 and restricted to the Pol V-loss of function. In conclusion, our results highlight a new role for Pol V on 5S rDNA, which is RdDM-independent and comes specifically at chromosome 4, in addition to the RdDM pathway.
植物特有的RNA聚合酶Pol IV和Pol V对于RNA指导的DNA甲基化（RdDM）至关重要，而这一过程还需要RDR2（RNA依赖性RNA聚合酶2）、DCL3（类Dicer 3）、AGO4（AGO蛋白4）和DRM2（结构域重排甲基转移酶2）的参与。RdDM专门负责对包括转座元件、多个蛋白质编码基因的调控区域以及5S rRNA编码DNA（rDNA）阵列在内的靶序列进行甲基化。在本文中，我们研究了5S-210转录本的表达情况，它是5S RNA基因沉默释放的一个标志物，以显示在植物早期发育过程中RNA聚合酶IV和V对5S rDNA阵列的不同影响。通过结合分子和细胞学分析，我们表明RdDM的参与者Pol IV、RDR2、DRM2和Pol V是维持4号和5号染色体上5S RNA基因转录沉默所必需的。此外，我们还发现了与4号染色体5S阵列特异性染色质解聚相关的去抑制现象，且这种现象仅限于Pol V功能丧失的情况。总之，我们的结果突出了Pol V在5S rDNA上的一个新作用，除了RdDM途径外，它在4号染色体上具有独立于RdDM的特定作用。
