Clavel Marion, Pélissier Thierry, Descombin Julie, Jean Viviane, Picart Claire, Charbonel Cyril, Saez-Vásquez Julio, Bousquet-Antonelli Cécile, Deragon Jean-Marc
BMC Plant Biol. 2015 Mar 3;15:70. doi: 10.1186/s12870-015-0455-z.
In plants and animals, a large number of double-stranded RNA binding proteins (DRBs) have been shown to act as non-catalytic cofactors of DICERs and to participate in the biogenesis of small RNAs involved in RNA silencing. We have previously shown that the loss of Arabidopsis thaliana's DRB2 protein results in a significant increase in the population of RNA polymerase IV (p4) dependent siRNAs, which are involved in the RNA-directed DNA methylation (RdDM) process.
Surprisingly, despite this observation, we show in this work that DRB2 is part of a high molecular weight complex that does not involve RdDM actors but several chromatin regulator proteins, such as MSI4, PRMT4B and HDA19. We show that DRB2 can bind transposable element (TE) transcripts in vivo but that drb2 mutants do not have a significant variation in TE DNA methylation.
We propose that DRB2 is part of a repressive epigenetic regulator complex involved in a negative feedback loop, adjusting epigenetic state to transcription level at TE loci, in parallel of the RdDM pathway. Loss of DRB2 would mainly result in an increased production of TE transcripts, readily converted in p4-siRNAs by the RdDM machinery.
在植物和动物中，大量双链RNA结合蛋白（DRB）已被证明可作为Dicer酶的非催化辅助因子，并参与RNA沉默中涉及的小RNA的生物合成。我们之前已经表明，拟南芥DRB2蛋白的缺失会导致依赖RNA聚合酶IV（p4）的小干扰RNA（siRNA）群体显著增加，这些小干扰RNA参与RNA指导的DNA甲基化（RdDM）过程。
令人惊讶的是，尽管有此观察结果，但我们在这项研究中表明，DRB2是一种高分子量复合物的一部分，该复合物不涉及RdDM相关因子，而是包含几种染色质调节蛋白，如MSI4、PRMT4B和HDA19。我们表明，DRB2在体内可以结合转座元件（TE）转录本，但drb2突变体在TE DNA甲基化方面没有显著变化。
我们提出，DRB2是一种抑制性表观遗传调节复合物的一部分，该复合物参与一个负反馈环，在RdDM途径的平行过程中，将TE位点的表观遗传状态调整到转录水平。DRB2的缺失主要会导致TE转录本产量增加，这些转录本很容易被RdDM机制转化为p4-siRNA。
