TONSOKU is required for the maintenance of repressive chromatin modifications in Arabidopsis

The stability of eukaryotic genomes relies on the faithful transmission of DNA sequences and the mainte-nance of chromatin states through DNA replication. Plant TONSOKU (TSK) and its animal ortholog TON-SOKU-like (TONSL) act as readers for newly synthesized histones and preserve DNA integrity via facilitating DNA repair at post-replicative chromatin. However, whether TSK/TONSL regulate the maintenance of chro-matin states remains elusive. Here, we show that TSK is dispensable for global histone and nucleosome accumulation but necessary for maintaining repressive chromatin modifications, including H3K9me2, H2A.W, H3K27me3, and DNA methylation. TSK physically interacts with H3K9 methyltransferases and Poly -comb proteins. Moreover, TSK mutation strongly enhances defects in Polycomb pathway mutants. TSK is intended to only associate with nascent chromatin until it starts to mature. We propose that TSK ensures the preservation of chromatin states by supporting the recruitment of chromatin modifiers to post-replicative chromatin in a critical short window of time following DNA replication.

Automated summary

Plant TONSOKU (TSK) and its animal ortholog TON-SOKU-like (TONSL) play a crucial role in maintaining chromatin stability during DNA replication. TSK interacts with histone modifiers and Polycomb proteins to preserve repressive chromatin modifications. TSK is specifically involved in a critical period of time following DNA replication to ensure the preservation of chromatin states.