Phase-separated TRB-PRC2 aggregates contribute to Polycomb silencing in plants

Local accumulation of Polycomb Repressive Complex 2 (PRC2) is essential to gene silencing. Liquid-liquid phase separation (LLPS) mechanism is emerging as a paradigm to concentrate transcriptional machinery for effective gene regulation. Here, we elucidate that a rice single Myb transcription factor TRBF2 forms phase-separated droplets, which aggregate with PRC2 through direct protein interaction. Furthermore, TRB1, the closest homolog of TRBF2 in Arabidopsis, also forms phase-separated aggregates with PRC2. Mutants of TRBF2 and PRC2 component CLF display similar developmental defects, share common differentially expressed genes, and reduced H3K27me3 chromatin regions. Chromatin immunoprecipitation analysis supports that TRBF2 concentrates PRC2 at target loci to promote H3K27me3 deposition. Therefore, we propose that the aggregation of the plant-specific TRBs with PRC2 by the LLPS mechanism contributes to Polycomb silencing. ### Competing Interest Statement The authors have declared no competing interest.