H2A ubiquitination is essential for Polycomb Repressive Complex 1-mediated gene regulation in Marchantia polymorpha

Polycomb repressive complex 1 (PRC1) and PRC2 are chromatin regulators maintaining transcriptional repression by depositing H2A mono-ubiquitination (H2Aub) or H3 lysine 27 tri-methylation (H3K27me3), respectively. While PRC1 is known to be required for transcriptional repression, the contribution of H2Aub in the Polycomb repressive system remains unclear in plants. Here, we directly test the requirement of H2Aub for gene repression in Marchantia polymorpha by generating point mutants in H2A that fail to be ubiquitinated by PRC1. These mutants show reduced H3K27me3 levels on the same target sites as mutants in PRC1 subunits MpBMI1 and the homolog MpBMI1L, revealing that PRC1-catalyzed H2Aub is essential for Polycomb system function. Furthermore, we demonstrate that H2Aub contributes to the PRC1-mediated silencing of genes and transposable elements. Together, our data provide evidence that H2Aub plays indispensable roles in the PRC1-initiated repressive system in Marchantia. ChIP-seq and RNA-seq