A research group including Associate Professor Wataru Yamori, Specially Appointed Assistant Professor Issei Nakazato, and Professor Shin-ichi Arimura of the Graduate School of Agricultural and Life Sciences at the University of Tokyo, Professor Hiroyoshi Matsumura of the College of Life Sciences at Ritsumeikan University, Professor Hiroshi Fukayama of the Graduate School of Agricultural Science at Kobe University, and Specially Appointed Professor Keiichi Namba of the Graduate School of Frontier Biosciences at the University of Osaka has successfully improved photosynthetic capacity and productivity. They achieved this by enhancing Rubisco, the central enzyme responsible for carbon fixation, to improve its catalytic efficiency using a unique chloroplast genome editing technology. They also confirmed a further improvement in performance under future predicted high-CO2 conditions. This technology is expected to be applied as a next-generation breeding technique. The results were published in Nature Communications on June 19.
Image courtesy of Wataru Yamori, Graduate School of Agricultural and Life Sciences, The University of Tokyo.
Crops such as rice and wheat belong to C3 plants, and Rubisco in these plants is known to have a low catalytic rate. In contrast, Rubisco in C4 plants such as maize has a high catalytic rate and shows high photosynthetic capacity. Model analyses have reported that if Rubisco from C4 plants could be introduced into C3 plants, photosynthetic capacity could improve by 20% to 50%. However, the gene for the large subunit, which carries out most of Rubisco's functions, is encoded in the chloroplast genome, making modification and editing difficult, and enhancing its performance had not been realized.
Therefore, using their uniquely developed chloroplast genome editing technology, the research group introduced point mutations into the Rubisco large subunit gene encoded in the chloroplast genome of Arabidopsis thaliana, a model C3 plant. They generated seven types of single-amino-acid-modified lines.
When analyzing the enzyme characteristics of each mutant, they confirmed that the catalytic rate (kcat) improved by approximately 10% in the mutant where the 309th methionine was substituted with isoleucine (M309I), and in the mutant where the 397th aspartic acid was substituted with asparagine (D397N). These two mutants showed an improvement in photosynthetic capacity of approximately 15%. It was also found that these Rubisco characteristics are shared with C4 plants. No changes other than in Rubisco occurred in these mutants.
Furthermore, when they sowed and grew the plants for 48 days under current atmospheric CO2 concentration conditions and high-CO2 conditions (approximately 500 ppm, assumed for the end of this century), both showed promoted growth, and increases in total leaf area and shoot dry weight compared to the wild type. Under the high-CO2 conditions, the promotion was even more pronounced.
Through structural analysis of Rubisco, the group also clarified that the structure of the enzyme reaction center had changed. In the future, they plan to apply this technology to major crops while also investigating further enhancements.
Journal Information
Publication: Nature Communications
Title: Chloroplast genome editing of Rubisco boosts photosynthesis and plant growth
DOI: 10.1038/s41467-026-73783-w
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.