Arabidopsis RAD23B regulates pollen development by mediating KRP1 degradation.

The ubiquitin (Ub)/26S proteasome system (UPS) plays a key role in plant growth, development, and survival by directing the turnover of numerous regulatory proteins. In UPS, ubiquitin-like (UBL) and ubiquitin-associated (UBA) domains function as hubs for ubiquitin-mediated protein degradation. RADIATION SENSITIVE23 (RAD23), which was identified as a UBL/UBA protein, contributed to cell cycle progression, stress response, ER proteolysis, and DNA repair. Here, we report pollen is arrested at the microspore stage in a null rad23b mutant. We demonstrated that RAD23B can directly interact with KIP-RELATED PROTEIN 1 (KRP1) through its UBL-UBA domains. In addition, overexpression plants of KRP1 resulted in pollen development defects, a phenotype similar to the rad23b mutant. Finally, RAD23B was found to promote the degradation of KRP1 in vivo, which was accumulated following treatment with MG132. In summary, these results indicate the important role of RAD23B in pollen development by controlling turnover of a key cell cycle protein, KRP1.