Histone H1 protects telomeric repeats from H3K27me3 invasion inArabidopsis

While the pivotal role of linker histone H1 in shaping nucleosome organization is well established, its functional interplays with chromatin factors along the epigenome are just starting to emerge. Here we first report that in Arabidopsis , as in mammals, H1 occupies Polycomb Repressive Complex 2 (PRC2) target genes where it favors chromatin condensation and H3K27me3 deposition. We further show that, contrasting with its conserved function in PRC2 activation at genes, H1 selectively prevents H3K27me3 accumulation at telomeres and large pericentromeric interstitial telomeric repeat (ITR) domains by restricting DNA accessibility to Telomere Repeat Binding (TRB) proteins, a group of H1-related Myb factors mediating PRC2 cis recruitment. This study unveils a mechanistic framework by which H1 avoids the formation of gigantic H3K27me3-rich domains at telomeric sequences and contributes to safeguard nucleus architecture. Abstract Figure Teano et al. report that that linker histone H1 and a group of H1-related telomeric proteins interplay to selectively influence the Polycomb repressive landscape at genes and telomeric repeats in Arabidopsis . These findings provide a mechanistic framework by which H1 influences the epigenome and nuclear organization in a sequence-specific manner. Highlights H1 promotes PRC2 activity and limits accessibility at a majority of genes H1 prevents PRC2 activity at telomeric DNA sequences PRC2 repression is achieved by restricting accessibility to TRB proteins H1 orchestrates the spatial organization of telomeres and interstitial telomeres (ITRs)