A coiled-coil protein associates Polycomb Repressive Complex2 (PRC2) to KNOX/BELL transcription factors for maintaining H3K27me3 and gene repression in shoot apex

PRC2 that mediates H3K27me3 deposition is important for developmental decisions in animals and plants. In plant shoot apical meristem, the Three Amino acid Loop Extension (TALE) family KNOX/BELL transcription factors are key regulators of meristem cell pluripotency maintenance and differentiation. In this work, we identify a PRC2-associated coiled-coil protein (PACP) that interacts with KNOX/BELL transcription factors in rice shoot apex cells. Loss-of-function mutation of PACP results in differential gene expression similar to that observed in knockdown plants of PRC2 genes and decreases genome-wide levels of H3K27me3 and the binding of the PRC2 core component EMF2b. We show that PACP binds to 6117 genes in shoot apex cells which are highly enriched for H3K27me3 and significantly overlap with genes bound by EMF2b and the rice KNOX1 protein Oryza sativa Homoebox1 (OSH1). In addition, we provide evidence that PACP is required for the repression of cell differentiation-promoting genes targeted by OSH1 in the shoot meristem. These data indicate that PACP is involved in the recruitment or stabilization of PRC2 to genes targeted by KNOX/BELL transcription factors to maintain H3K27me3 and gene repression in dividing cells of the shoot apex. The results provide insight into the chromatin mechanism by which KNOX/BELL proteins regulate shoot meristem development.