Functional redundancy and divergence of β-carbonic anhydrases in Physcomitrella patens

β-carbonic anhydrases, which function in regulating plant growth, C/N status, and stomata number, showed functional redundancy and divergence in Physcomitrella patens. Carbonic anhydrases (CAs) catalyze the interconversion of CO₂ and HCO₃^-. Plants have three evolutionarily unrelated CA families: α-, β-, and γ-CAs. βCAs are abundant in plants and are involved in CO₂ assimilation, stress responses, and stomata formation. Recent studies of βCAs have mainly examined C₃ or C₄ plants, whereas their functions in non-vascular plants are mostly unknown. In this study, phylogenetic analysis revealed that the evolution of βCAs were conserved between subaerial green algae and bryophytes after terrestrialization event, and βCAs from some cyanobacteria might begin evolving for the adaptation of terrestrial environment/habitat. In addition, we investigated the physiological roles of βCAs in the basal land plant Physcomitrella patens. High PpβCA expression levels in different tissues suggest that PpβCAs play important roles in development in P. patens. Plants treated with 1-10 mM NaHCO₃ had higher fresh and dry weight, PpβCA expression, total CA activity, and photosynthetic yield (Fv/Fm) compared with water-treated plants. However, treatment with 10 mM NaHCO₃ influenced the C/N status. Further study of six Ppβca single-gene mutants revealed that PpβCAs have functional redundancy and divergence in regulating the C/N ratio of plants and stomatal formation. This study provides new insight into the physiological roles of βCAs in basal land plants.