DNA methylation is associated with transcriptional repression of eukaryotic genes and transposons, but the downstream mechanism of gene silencing is largely unknown. Here, we describe two Arabidopsis thaliana methyl-CpG–binding domain proteins, MBD5 and MBD6, that are recruited to chromatin by recognition of CG methylation, and redundantly repress a subset of genes and transposons without affecting DNA methylation levels. These methyl readers recruit a J-domain protein, SILENZIO, that acts as a transcriptional repressor in loss-of-function and gain-of-function experiments. J-domain proteins often serve as co-chaperones with HSP70s. Indeed, we found that SILENZIO’s conserved J-domain motif was required for its interaction with HSP70s and for its silencing function. These results uncover an unprecedented role of a molecular chaperone J-domain protein in gene silencing downstream of DNA methylation.

DNA甲基化与真核基因和转座子的转录抑制有关，但基因沉默的下游机制很大程度上未知。在这里，我们描述了两种拟南芥甲基CpG 结合域蛋白 MBD5 和 MBD6，它们通过识别 CG 甲基化而被招募到染色质，并冗余地抑制基因和转座子的子集，而不影响 DNA 甲基化水平。这些甲基读取器招募一种 J 结构域蛋白 SILENZIO，该蛋白在功能丧失和功能获得实验中充当转录抑制因子。 J 结构域蛋白通常充当 HSP70 的共伴侣。事实上，我们发现 SILENZIO 的保守 J 结构域基序是其与 HSP70 相互作用及其沉默功能所必需的。这些结果揭示了分子伴侣 J 结构域蛋白在 DNA 甲基化下游基因沉默中发挥的前所未有的作用。