Linker histones mediate sequence-specific regulation of chromosomal organization and H3K27me3 enrichment over genes and telomeric repeats (ATAC-Seq)

Chromatin architecture relies on histone H1 whose central globular domain (GH1) sits on the nucleosome dyad and carboxy-terminal domain associates with linker DNA. We report that Arabidopsis H1 positively influences H3K27me3 chromatin enrichment over protein-coding genes but oppositely prevents its accumulation on telomeres and heterochromatic Interstitial Telomeric Repeats (ITRs). Contrasting with their neighboring heterochromatic environment, pericentromeric ITR regions remain highly compacted and are more prone to long-distance interactions with telomeres in H1 mutant plants. The switch from H1-rich to H3K27me3-rich ITR chromatin is further accompanied by an invasion of GH1-Myb Telomeric Repeat Binding protein 1 (TRB1), a structural component of telomeres capable to trigger H3K27me3 deposition over protein-coding genes displaying short telomeric motifs. This dual effect led us to propose a competition mechanism between H1 and TRB that prevents massive H3K27me3 deposition over large blocks of repeated motifs, thereby contributing to regulate H3K27me3 homeostasis over the genome. Examination of chromatin accessibility in WT and 2h1 plants by ATAC-seq.

染色质结构的维持依赖于组蛋白H1：其中心球状结构域（GH1）结合于核小体二分体，羧基末端结构域则与连接DNA相互作用。本研究发现，拟南芥中的组蛋白H1对蛋白编码基因区域的组蛋白H3赖氨酸27三甲基化（H3K27me3）染色质富集具有正向调控作用，但却反向抑制该修饰在端粒与异染色质间质端粒重复序列（Interstitial Telomeric Repeats, ITRs）上的积累。与周边异染色质环境不同，H1突变体植物中的着丝粒旁ITR区域仍保持高度致密状态，且更易与端粒发生长距离相互作用。从富含H1的染色质向富含H3K27me3的ITR染色质发生转变的过程中，伴随有GH1-Myb型端粒重复结合蛋白1（Telomeric Repeat Binding protein 1, TRB1）的入侵——该蛋白作为端粒的结构组分，能够在携带短端粒基序的蛋白编码基因上诱导H3K27me3的沉积。基于这种双重效应，我们提出H1与TRB之间存在竞争调控机制，该机制可阻止大量重复基序组成的大片段区域发生H3K27me3沉积，从而有助于维持基因组范围内的H3K27me3稳态。本研究通过ATAC-seq技术检测了野生型（Wild Type, WT）与h1突变体植物的染色质可及性。