In light of the growing world population, researchers around the world are searching for new strategies to increase food security. One such strategy is to improve photosynthesis and thus crop growth. A feasibility study now shows that it is in principle possible to transfer a carbon dioxide fertilizing bacterial system to 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 Rubico enzyme, which is responsible for carbon dioxide fixation. This is because the rate at which Rubisco converts carbon dioxide is low, plus the enzyme does not adequately distinguish between carbon dioxide and oxygen (O2), which reduces efficiency even further. Some bacteria circumvent this problem by evolving so-called carbon dioxide concentration mechanisms. In the so-called carboxysomes, Rubisco is surrounded by a protein envelope in which carbon dioxide is enriched. This way Rubisco works more efficiently.
Nine bacterial genes were transferred
A team led by Taiyu Chen of the University of Liverpool in Great Britain has succeeded in transposing this bacterial system into plants for the first time. Halothiobacillus neapolitanus served as the basis. Nine genes encoding for individual components of the carboxysomes. While the scientists had only transferred individual components to plants in previous experiments, Chen and his colleagues transferred all nine genes into the chloroplasts of tobacco plants.
Indeed: “Our results show that carboxysomes from at least nine groups of sclerosis and catalytically active rubisco are formed in the chloroplasts of tobacco plants,” the authors report. The components self-assemble in the tobacco plant to form functional carboxysomes. Structural analyzes revealed that the structure of the carboxysomes in chloroplasts is similar to the normal version in bacteria.
There is no growth in the surrounding air yet
However, transgenic plants produced in this way cannot grow in normal ambient air with a carbon dioxide content of around 440 parts per million (ppm). However, if the team increased the concentration of carbon dioxide in the air to one percent, the transgenic plants evolved similarly to the unmodified control plants—albeit somewhat more slowly. “There is a need for further improvement in building design so that plants can also grow in the natural ambient air,” says the research team. “But at least growing transgenic plants with one percent carbon dioxide indicates that the catalytic activities of modified carboxysomes in chloroplasts could essentially support plant photosynthesis.”
Although the technology is not yet ready for use, the feasibility study shows that corresponding modifications are basically possible. “The transgenic lines generated in this study will facilitate the further development of carboxysome engineering,” the authors say. “Our study provides evidence that it is possible to engineer fully functional CO2 fixers and fully functional CO2 concentration mechanisms into green makers to enhance photosynthesis and plant productivity.”
Source: Taiyu Chen (University of Liverpool, UK) et al., Nature Communications, Available here. doi: 10.1038/s41467-023-37490-0
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