Synergistic role of Rubisco inhibitor release and degradation in photosynthesis

Summary Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) exhibits catalytic promiscuity, resulting in error‐prone reactions and the formation of inhibitory sugar phosphates. Specifically, Xylulose‐1,5‐bisphosphate (XuBP) acts as an inhibitor by binding to the active site of Rubisco, thereby impairing its catalytic function. Thermolabile Rubisco activase (Rca) facilitates the release of such inhibitors, including XuBP, by remodelling Rubisco. In Arabidopsis thaliana , the phosphatase pair CbbYA and CbbYB subsequently hydrolyses XuBP to prevent its rebinding to Rubisco. To explore the functional interplay between these components in maintaining photosynthesis, cbbya , cbbyb and cbbyab mutants were crossed with RCA knockdown ( rca‐2 ) lines. Additionally, both RCA and CBBYA were overexpressed in wild‐type (WT) Arabidopsis thaliana . Phenotypic analyses revealed an exacerbation in decreased growth and photosynthetic efficiency in the cbbyab rca‐2 double mutants compared with the control mutants ( cbbyab and rca‐2 ), indicating a negative genetic interaction. Furthermore, the co‐overexpression of RCA and CBBYA did not improve photosynthesis under short‐term heat stress, and light reactions were adversely affected relative to the WT. These findings illustrate the synergistic roles of Rca, CbbYA and CbbYB in maintaining carbon fixation and promoting plant growth in Arabidopsis thaliana . Thus, the coordinated regulation of Rca and CbbY enzymes is crucial for optimizing photosynthetic efficiency.