H2A monoubiquitination targeting by cohesin subunits in Arabidopsis

Histone H2A monoubiquitination (H2Aub1) function as a conserved post-translational modification in eukaryotes to maintain gene repression and ensure cellular identity. Arabidopsis H2Aub1 is catalyzed by polycomb repressive complex 1 (PRC1) contributed by AtRING1s and AtBMI1s. Because PRC1 components lack known DNA binding domains, how H2Aub1 is established at the specific genomic sites remains a topic of debate. Here we show that the cohesin subunits AtSYN4 and AtSCC3 interact with each other and AtSCC3 binds to AtBMI1s. We find that H2Aub1 levels are significantly reduced in the atsyn4 mutant or AtSCC3 RNAi knockdown plants. ChIP-seq analysis indicated that AtSYN4 and AtSCC3 tend to associate with H2Aub1 in the genome regions of transcription activation independent on H3K27me3. Finally, we show that AtSYN4 binds directly to the G-box element and targets H2Aub1to these sites. Our study thus revealed a mechanism for cohesin-mediated recruitment of AtBMI1s to specific loci to mediate H2Aub1. Detecting the genome-wide occupancy of AtSYN4 and AtSCC3.