Engineering an inorganic carbon highway to improve C3 photosynthesis

Photosynthesis remains a target for genetic engineering that exhibits great potential for enhancing crop yield, in addition to its important role in reducing atmospheric carbon dioxide. Photosynthesis provides most of the world’s biomass through carbon fixation. By learning how to provide increased bicarbonate to the carbon-fixing enzyme Rubisco in a model plant, technology is being developed that can be applied to crop plants.

This project uses synthetic biology approaches to increase bicarbonate supply to Rubisco, and consequently enhance photosynthesis, in a model plant. Trainees are engaged in multidisciplinary projects involving genetics, biochemistry, and molecular biology. Undergraduates from diverse groups are gaining research experience during the academic year and summer months.

A new effort to educate the public is occurring through instructive videos on a website and Youtube channel. Collaboration with a Public Broadcasting Service station is planned to create a professional video explaining the use of synthetic biology to enhance photosynthesis and the role of plants in removing carbon dioxide from the atmosphere. The video is to be made available through PBS Learning Media for K-12 education.

C3 crop plants, which constitute approximately 85 percent of plants, including food crops like soybean and wheat, lack the ability to concentrate carbon dioxide near Rubisco. Synthesis of a carbon-concentrating mechanism (CCM) in crop plants, based on ones that exist in cyanobacteria and algae, has the potential to substantially increase yields. Installation of a microcompartment-based CCM requires not only the actual construction of the microcompartment within the chloroplast, but also the provision of additional bicarbonate that can be converted into carbon dioxide.

In order to assess whether bicarbonate transporters from microorganisms can function in the chloroplast, their encoding genes are being transformed into a mutant background in which chloroplast carbonic anhydrase has been removed. The absence of carbonic anhydrase in the mutant causes an impaired, bicarbonate-deficient, phenotype that is predicted to be rescued by a functional bicarbonate transporter.

The transformed plants are being analyzed not only for the rescue of the bicarbonate-requiring phenotype, but also for effects on photosynthesis, growth, reactive oxygen species, stromal pH, and fatty acid synthesis. In addition to providing an essential step in the transformative engineering of C3 plants with carbon-concentrating mechanisms, modeling predicts that yield can be enhanced by the mere incorporation of inorganic carbon pumps into chloroplasts, even before a full microcompartment-based CCM is installed.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.