In view of the growing world population, researchers around the world are looking for new strategies to increase food security. One of these strategies is to improve photosynthesis and thus the growth of crops. A feasibility study now shows that it is in principle possible to transfer a bacterial system for CO2 enrichment into crops in order to increase the rate of photosynthesis. Although the technology is not yet ready for use, it provides a basis for further developments.
During photosynthesis, plants convert carbon dioxide and water into sugar and oxygen with the help of sunlight. However, the process is limited by the inefficiency of the Rubisco enzyme, which is responsible for fixing carbon dioxide. This is because the rate at which Rubisco converts the CO2 is low and, in addition, the enzyme does not distinguish sufficiently between CO2 and oxygen (O2), which further reduces efficiency. Certain bacteria circumvent this problem by developing so-called CO2 concentration mechanisms. In their so-called carboxysomes, Rubisco is surrounded by a protein shell within which CO2 is enriched. This way Rubisco works more efficiently.
Nine bacterial genes transferred
A team led by Taiyu Chen from the University of Liverpool in Great Britain has now successfully transferred this bacterial system to plants for the first time. The bacterium Halothiobacillus neapolitanus served as the basis. Nine genes code for the individual components of the carboxysomes. While scientists have only transferred individual components to plants in previous experiments, Chen and his colleagues transferred all nine genes to the chloroplasts of tobacco plants.
And indeed: “Our results show that carboxysomes from at least nine groups of building blocks and catalytically active Rubisco are formed in the chloroplasts of the tobacco plants,” the authors report. The components self-assembled in the tobacco plant to form functional carboxysomes. Structural analyzes revealed that the structure of the carboxysomes in the chloroplasts resembles the natural version in the bacteria.
No growth in ambient air yet
However, the transgenic plants produced in this way could not grow in normal ambient air with a CO2 content of around 440 parts per million (ppm). However, if the team increased the CO2 concentration in the air to one percent, the transgenic plants developed similarly to unmodified control plants – albeit somewhat more slowly. “Further optimization of the construct design is required so that the plants can also grow in normal ambient air,” says the research team. “But at least the growth of the transgenic plants at one percent CO2 indicates that the catalytic activities of the modified carboxysomes in the chloroplasts could fundamentally support the photosynthesis of the plant.”
Although the technology is not yet ready for use, the feasibility study shows that corresponding modifications are fundamentally possible. “The transgenic lines generated in this study will facilitate the further development of carboxysome engineering,” say the authors. “Our study provides evidence that it is possible to engineer fully functional CO2 fixation modules and entire CO2 concentration mechanisms into chloroplasts to enhance photosynthesis and plant productivity.”
Source: Taiyu Chen (University of Liverpool, UK) et al., Nature Communications, doi: 10.1038/s41467-023-37490-0