PRC1‐Mediated H2Aub Loop Formation and Function in <i>Arabidopsis</i>

Polycomb group (PcG) complexes play a crucial role in the regulation of gene repression and in organizing the 3D conformation of chromatin. However, while Polycomb Repressive Complex (PRC) 2 mediated H3K27me3 clearly contributes to the formation of repressive chromatin loops in Arabidopsis, the role of PRC1 mediated H2Aub remains unclear. Notably, in the Arabidopsis genome, H2Aub and H3K27me3 marks do not always co-localize, and some regions are marked exclusively by H2Aub, but the contribution of these only-H2Aub regions to chromatin looping remains largely unexplored. By using Capture-High-throughput Chromosome Conformation Capture (C-Hi-C) to specifically enrich interactions associated with H2Aub regions, it is find that H2Aub loops are preferentially established between two H2Aub enriched regions. Although pure only-H2Aub-loops can be detected, H2Aub regions tend to interact with regions marked by both H2Aub and H3K27me3, contributing to the formation of PcG hubs. Furthermore, it is find that maintaining appropriate level of H2Aub and H3K27me3 is essential for the stability of H2Aub loops and that the formation of these loops reinforce gene repression. This findings unveil the existence of H2Aub loops in Arabidopsis and their impact on transcriptional regulation.