The role of ATXR6 expression in modulating genome stability and transposable element repression in Arabidopsis [ChIP-seq_25]. The role of ATXR6 expression in modulating genome stability and transposable element repression in Arabidopsis [ChIP-seq_25]

ARABIDOPSIS THRITHORAX-RELATED PROTEINS 5 (ATXR5) AND ATXR6 are required for the deposition of H3K27me1 and for maintaining genomic stability in Arabidopsis. Reduction of ATXR5/6 activity results in activation of DNA damage response genes, along with tissue-specific derepression of transposable elements, chromocenter decompaction, and genomic instability characterized by accumulation of excess DNA from heterochromatin. How loss of ATXR5/6 and H3K27me1 leads to these phenotypes remains unclear. Here we provide extensive characterization of the atxr5/6 hypomorphic mutant by comprehensively examining gene expression and epigenetic changes in the mutant. We found that the tissue-specific phenotypes of TE derepression and excessive DNA in this atxr5/6 mutant correlated with residual ATXR6 expression from the hypomorphic ATXR6 allele. However, upregulation of DNA damage genes occurred regardless of ATXR6 levels and thus appears to be a separable process. We also isolated an atxr6 null allele which showed that ATXR5 and ATXR6 are required for female germline development. Finally, we characterize three previously reported suppressors of the hypomorphic atxr5/6 mutant and show that these rescue atxr5/6 via distinct mechanisms, two of which involve increasing H3K27me1 levels. Overall design: Examination of H3K27me1 profiles in 4-week-old rosette leaves in atxr5/6 (W) mutants.

拟南芥Trithorax相关蛋白5（ATXR5）与ATXR6是组蛋白H3赖氨酸27单甲基化（H3K27me1）沉积以及维持拟南芥基因组稳定性所必需的蛋白。ATXR5/6活性降低会激活DNA损伤响应基因，同时伴随转座因子（transposable elements, TE）的组织特异性去抑制、染色质中心解压缩，以及以异染色质来源过量DNA积累为特征的基因组不稳定现象。目前尚不明确ATXR5/6功能缺失与H3K27me1水平下降如何引发上述表型。本研究通过全面分析亚效atxr5/6突变体的基因表达与表观遗传变化，对其进行了系统表征。研究发现，该突变体中转座因子去抑制与过量DNA积累的组织特异性表型，与亚效ATXR6等位基因残留的ATXR6表达水平相关。然而，DNA损伤基因的上调并不依赖于ATXR6的表达水平，因此这一过程似乎与前述表型相互独立。本研究还分离得到了atxr6功能缺失等位基因（null allele），实验结果表明ATXR5与ATXR6对于雌性生殖系发育不可或缺。最后，本研究对此前报道的3种atxr5/6亚效突变体抑制子进行了表征，证实这些抑制子通过不同机制挽救atxr5/6突变表型，其中两种机制涉及提升H3K27me1水平。总体实验设计：检测atxr5/6（W）突变体4周龄莲座叶的H3K27me1修饰图谱。