Removal of H2Aub1 by ubiquitin-specific proteases 12 and 13 is required for stable Polycomb-mediated gene repression in Arabidopsis

Background: Stable gene repression is essential for normal growth and development. Polycomb Repressive Complexes 1 and 2 (PRC1 & PRC2) are involved in this process by establishing monoubiquitinated histone 2A (H2Aub1) and subsequent trimethylation of lysine 27 of histone 3 (H3K27me3). Previous work proposed that H2Aub1 removal by the ubiquitin-specific proteases 12 and 13 (UBP12 & UBP13) is part of the repressive PRC1&2 system, but its functional role remains elusive. Results: We show that UBP12 and UBP13 work together with PRC1, PRC2, and EMF1 to repress genes involved in stimulus response. We found that H2Aub1 is associated with responsiveness, and that it’s only indirectly repressive via PRC2 recruitment. Our analyses also revealed that PR2 targets that do not require PRC1 are pre-repressed. Lastly, we have found that removal of H2Aub1 by UBP12/13 prevents loss of H3K27me3, consistent with our finding that the H3K27me3 demethylase REF6 is enriched at H2Aub1 marked genes. Conclusions: Our data allow us to propose a model in which deposition of H2Aub1 permits recruitment of PRC2 and provides a state that allows for a rapid switch between gene activation and repression. Removal of H2Aub1 by UBP12/13 is required to achieve stable repression. RNAseq of single and double mutants for the UBP12/13 genes, plus wild-type control, three biological replicates of each genotype. Three ChIP-seq experiments on the double mutant and wild-type; the first including H2Aub1, H2A.Z, H3, and input. The second including H3K27me3, and H3. The third including REF6 (GFP), and input. Two biological replicates were included for each genotype * IP combination.