OsCBL5-CIPK1-PP23 module enhances rice grain size and weight through the gibberellin pathway.

Grain size is a key factor in determining rice yield and exploring new pathways to regulate grain size has immense potential to improve yield. In this study, we report that OsCBL5 encodes a calcineurin B subunit protein that significantly promotes grain size and weight. oscbl5 plants produced obviously smaller and lighter seeds. We further revealed that OsCBL5 promotes grain size by affecting cell expansion in the spikelet hull. Biochemical analyses demonstrated that CBL5 interacts with CIPK1 and PP23. Furthermore, double and triple mutations were induced using CRISPR -Cas9 (cr) to analyze the genetic relationship. It was found that the cr-cbl5/cipk1 phenotype was similar to cr-cipk1, and that the cr-cbl5/pp23, cr-cipk1/pp23, and cr-cbl5/cipk1/pp23 phenotype was similar to cr-pp23, indicating that OsCBL5, CIPK1 and PP23 act as a molecular module in influencing seed size. In addition, the results show that both CBL5 and CIPK1 are involved in the GA pathway and significantly affect the accumulation of endogenous active GA4. PP23 participates in GA signal transduction. In brief, this study identified a novel rice grain size regulation module OsCBL5-CIPK1-PP23, which could potentially be targeted for improving rice yield.