Enhanced salt stress tolerance in plants without growth penalty through increased photosynthesis activity by plastocyanin from Antarctic moss

SUMMARY Salinity poses a significant challenge to plant growth and crop productivity by adversely affecting crucial processes, including photosynthesis. Efforts to enhance abiotic stress tolerance in crops have been hindered by the trade‐off effect, where increased stress resistance is accompanied by growth reduction. In this study, we identified and characterized a plastocyanin gene ( PaPC ) from the Antarctic moss Polytrichastrum alpinum , which enhanced photosynthesis and salt stress tolerance in Arabidopsis thaliana without compromising growth. While there were no differences in growth and salt tolerance between the wild type and Arabidopsis plastocyanin genes ( AtPC1 and AtPC2 )‐overexpressing plants, PaPC ‐overexpressing plants demonstrated superior photosynthetic efficiency, increased biomass, and enhanced salt tolerance. Similarly, PaPC ‐overexpressing rice plants exhibited improved yield potential and photosynthetic efficiency under both normal and salt stress conditions. Key amino acid residues in PaPC responsible for this enhanced functionality were identified, and their substitution into AtPC2 conferred improved photosynthetic performance and stress tolerance in Arabidopsis, tobacco, and tomato. These findings not only highlight the potential of extremophiles as valuable genetic resources but also suggest a photosynthesis‐based strategy for developing stress‐resilient crops without a growth penalty.