In a study led by Wen-Hui Shen at IBMP, an important advance has been made in understanding the epigenetic mechanisms that control plant development. Published in The Plant Journal, this work focuses on the Polycomb Repressive Complex 1 (PRC1), a major regulator of transcriptional gene silencing. While the function of PRC2 and its role in depositing the repressive histone mark H3K27me3 are now well established, the molecular mechanisms underlying PRC1 activity in plants have remained largely elusive.
The researchers investigated AtRING1, a core component of PRC1 that contains two distinct domains: an N-terminal RING domain associated with enzymatic activity and a C-terminal RAWUL domain. Using CRISPR/Cas9 genome editing, they generated a series of mutants that allowed them to dissect the specific contributions of these domains. Their results show that complete loss of AtRING1 leads to severe defects in cell differentiation, with the formation of embryonic callus-like structures, highlighting the essential role of PRC1 in maintaining cellular identity. In contrast, mutants lacking only the RAWUL domain display milder developmental phenotypes, indicating that the RING domain retains partial activity. A key finding of the study is the specific role of the RAWUL domain in ensuring efficient monoubiquitination of histone H2A (H2Aub1), a hallmark of PRC1 function. The authors show that this domain is required for proper H2Aub1 accumulation at target genes and also influences, in a locus-dependent manner, the deposition of H3K27me3. These results provide new insights into the functional relationship between PRC1 and PRC2. Contrary to the classical model in which PRC2 acts upstream of PRC1, the study suggests that PRC1 activity, through H2Aub1 deposition, can precede and facilitate PRC2 recruitment at specific loci. Finally, the study reveals that the RAWUL domain contributes to the regulation of key developmental processes such as germination, vegetative phase transition and flowering time, underscoring its role in fine-tuning gene expression.
By uncovering the critical function of the RAWUL domain in PRC1 activity and its interplay with PRC2, this work provides a major advance in our understanding of epigenetic regulation in plants.
