BMI1s interact with condensin complexes to regulate chromatin 3D structure and gene expression in Arabidopsis

The accurate chromatin states are essential for maintaining genome integrity and ensuring the normal transcription of genes. Polycomb group (PcG) proteins regulate chromatin states not only by modifying the chromatin, but also by influencing the chromatin three-dimensional (3D) structure. The core components of Polycomb repressive complex 1 (PRC1), B LYMPHOMA MOLONEY MURINE LEUKEMIA VIRUS INSERTION REGION 1 HOMOLOG 1A/B/C (BMI1s), have been reported to maintain the compartment domains (CDs) generally, but the mechanism by which they function remains elusive. Here, we reveal that condensin complexes, whose function are related to chromatin or chromosome, can interact with BMI1s. Removal of condensin I or II also leads to global impairment of CDs. The significantly impaired CDs in bmi1a/b/c and condensin mutants are basically the same and the CDs co-regulated by BMI1s and condensin complexes have higher strength in the wild-type (WT, Col-0) plant, indicating that BMI1s and condensin complexes cooperate to maintain CDs. This regulatory function is parallel to the function of histone modifications deposited by PcG in maintaining CDs, since removal of either condensin I or II does not obviously disrupt the genome-wide level of H3K27me3 and H2AK121ub. Moreover, we discovered that BMI1s and condensin complexes jointly influence the expression of a portion of genes to enable normal plant growth and may maintain the genome integrity under stress conditions. Thus, our work proides a perspective for the gene expression and epigenetic regulatory mechanism of PRC1, in Arabidopsis, in addition to histone modifications.