OsαCA1 Affects Photosynthesis, Yield Potential, and Water Use Efficiency in Rice

Plant growth and crop yield are essentially determined by photosynthesis when considering carbon dioxide (CO₂) availability. CO₂ diffusion inside a leaf is one of the factors that dictate the CO₂ concentrations in chloroplasts. Carbonic anhydrases (CAs) are zinc-containing enzymes that interconvert CO₂ and bicarbonate ions (HCO₃^-), which, consequently, affect CO₂ diffusion and thus play a fundamental role in all photosynthetic organisms. Recently, the great progress in the research in this field has immensely contributed to our understanding of the function of the β-type CAs; however, the analysis of α-type CAs in plants is still in its infancy. In this study, we identified and characterized the OsαCA1 gene in rice via the analysis of OsαCAs expression in flag leaves and the subcellular localization of its encoding protein. OsαCA1 encodes an α-type CA, whose protein is located in chloroplasts with a high abundance in photosynthetic tissues, including flag leaves, mature leaves, and panicles. OsαCA1 deficiency caused a significant reduction in assimilation rate, biomass accumulation, and grain yield. The growth and photosynthetic defects of the OsαCA1 mutant were attributable to the restricted CO₂ supply at the chloroplast carboxylation sites, which could be partially rescued by the application of an elevated concentration of CO₂ but not that of HCO₃^-. Furthermore, we have provided evidence that OsαCA1 positively regulates water use efficiency (WUE) in rice. In summary, our results reveal that the function of OsαCA1 is integral to rice photosynthesis and yield potential, underscoring the importance of α-type CAs in determining plant physiology and crop yield and providing genetic resources and new ideas for breeding high-yielding rice varieties.