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

This study  is  led  by  Dr.  Yue  Zhou  (State  Key  Laboratory  of  Gene  Function  and  Modulation Research, School of Advanced Agricultural Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China).

The accurate chromatin states are essential for maintaining the 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), are the E3 ligase to deposit H2AK121ub in Arabidopsis. As for chromatin 3D structure, BMI1s have been reported to maintain the compartment domains (CDs) generally, but the mechanism by which they function remains elusive.

The  authors  first  identified  a  BMI1A  interactor  CAP-H,  which  is  the  subunit  of  condensin complexes, through yeast two-hybrid screening. Condensin complexes belong to SMC (Structural Maintenance of Chromosome) complexes that have the ability to organize the chromatin especially in cell division, while how they participate in chromatin 3D regulation in interphase is less known. Therefore, the authors speculated that the BMI1s and condensin complexes may co-regulate CD structure through interaction.

After confirming the interactions between condensin I/II and BMI1s, the authors compared the molecular phenotypes in bmi1a/b/c and condensin mutants, and found that removal of either condensin I or condensin II does not lead to the disruption of histone modifications deposited by PcG, indicating that BMI1s and condensin complexes may cooperatively regulate other aspects. Through Hi-C experiments, the authors discovered that both BMI1s and condensin complexes maintain the interactions within CD, and most of CDs are coregulated by them. Moreover, the

maintenance of the CDs that have strong interaction strength needs the cooperative roles of the three complexes.  Finally, analyzing the expression changes, the authors discovered that the BMI1s and condensin complexes also co-regulate the expression of a portion of genes to enable normal plant growth and may maintain the stability of 3D genome under stress conditions.

See the article:

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

https://link.springer.com/article/10.1007/s42994-025-00202-x