CAPP: Combining Plant and Algal Photosynthesis

In most plants, growth rate is limited by the rate at which carbon dioxide from the atmosphere is taken up and converted to sugars in the process of photosynthesis. The enzyme responsible for the first step in this process, Rubisco, does not work at its potential maximum efficiency at the current levels of carbon dioxide present in the atmosphere. If levels were much higher, photosynthesis would be faster and plants would grow faster. This speeding-up of photosynthesis will happen naturally over the next fifty years or so as atmospheric carbon dioxide levels rise due to human activities. However, there is an immediate requirement for increased crop productivity to provide food for the rising population of the planet. Our project addresses this problem. We are studying a mechanism present in tiny green algae that results in high concentrations of carbon dioxide inside their photosynthesising cells (called a Carbon Concentrating Mechanism, or CCM), enabling Rubisco to work at maximum efficiency. We have recently discovered important new information about this mechanism, and we have invented new and rapid methods to discover algal genes that contribute to it. We have two complementary and parallel aims. First, we will apply our new methods to identify all of the genes required by the algae to achieve high concentrations of carbon dioxide inside the cells, and we will discover exactly how these genes work. Second, we will transfer the most important genes into a plant, and study whether the same CCM can be recreated inside a leaf. If it can, we expect that our experimental plant will have higher rates of photosynthesis and hence a higher rate of growth than normal plants. This work will provide new insights into how plants and algae acquire and use carbon dioxide from the atmosphere, of great importance in predicting and coping with the current rapid changes in the atmosphere and hence in climate. The work will also contribute to strategies to increase global food security, because it will indicate new ways in which crop productivity can be increased.

We propose to use the carbon concentrating mechanism (CCM) from green algae to enhance CO2 concentration in C3 chloroplasts, suppressing photorespiration and increasing productivity. The CAPP programme will discover and characterise components of the Chlamydomonas CCM, in addition to known bicarbonate pump(s) and carbonic anhydrases, identify pyrenoid components, supramolecular complexes and their chaperones, and progressively incorporate key components into Arabidopsis. Our approach includes: 1) Addition of a bicarbonate pump to the chloroplast envelope inner membrane (and removal of any CO2-channelling aquaporins: PIP1 sub-family) to maximize bicarbonate accumulation in the chloroplast. 2) Formation of ordered clusters of modified Rubisco and carbonic anhydrase in the chloroplast to benefit from local CO2 concentration at the active sites, and to distance the Rubisco from the site of O2 generation at PSII. 3) Discovery of genes required for the CCM in Chlamydomonas through a novel, high throughput insertional mutant screen and parallel, hypothesis-driven RNAi approaches 3) Progressive addition of newly-discovered CCM components into an Arabidopsis plant incorporating the above novel features, followed by characterisation of the metabolism and physiology of the lines thus generated 4) Mathematical modelling methods to identify constraints to carbon uptake and exchange in Chlamydomonas and Arabidopsis, and to evaluate the improvement in carbon supply likely to arise as CCM components are added to Arabidopsis. The goal is to create an Arabidopsis 'Advanced Plant', with significantly improved rates of CO2 assimilation. This is a first step towards producing a crop plant with a 'biophysical' CCM that significantly improves productivity and yield.

Who will benefit from this research? 1. Academics and researchers in all fields of plant research. 2. Annotators in genomics and metabolomics, database and germplasm curators. 3. UK, US and international science base. 4.Agro-industry including biotechnologists and plant breeders seeking to increase plant productivity and/or harvest index; metabolic engineers and metabolic modellers. 5. Agricultural community and advisors. 6. Postdoctoral researchers employed on the project. 7. Public 8. The next generation: school children and undergraduate students 9. Multinational and Government Agencies How will they benefit from this research? 1. Researchers will receive comprehensive new information about the CCM of algae, requirements for CO2 concentration in higher-plant chloroplasts, and mechanisms of assembly of supra-molecular complexes. 2. Researchers will have access at the point of publication to new genome annotation in Chlamydomonas, novel Arabidopsis material with altered primary carbon assimilation and models describing the relationship between the spatial distributions of inorganic carbon substrates and enzymes and the process of CO2 assimilation in chloroplasts. 3. The research will have a major impact on understanding of photosynthetic CO2 assimilation and its relationship to inorganic carbon concentrations in the chloroplast. 4. Agro-industry will receive information to underpin rational approaches to increase plant productivity, and relevant new genes and modelling methodologies. 5. The agricultural community will benefit in the longer term from sustainable crop improvements enabled by our research. 6. The PDRAs will receive a wide training in plant integrative biology, professional skills and wider training courses, and the opportunity to interact closely with researchers on an international scale. They will also receive training in transferable skills such as presentation and dissemination of results, and grant-writing. 7. Our research findings relate to issues of public interest including sustainable crop production, global food security and atmospheric and climate change. 8. Our research has wide educational value, at all levels through schools and Universities 9. Our research is relevant to broad international challenges in sustainable agriculture, food security, and public awareness of these issues What will be done to ensure they benefit from this research? 1. Publish results in high-impact journals in a timely fashion, with open access where possible. Present research results at international meetings and institutions 2. Submit data and models to relevant international depositories. Notify new/corrected gene and enzyme annotations to community databases 3. Exploit extensive existing contacts of the PIs with other academics with relevant research interests as soon as any exploitable results/materials are generated. 4. Make informal contacts with biotechnologists as soon as exploitable results are generated; recognise and protect PI to ensure wise and fruitful exploitation. Collectively we have vibrant contacts with relevant industries. 6. Provide information and mentoring to ensure uptake of postdoctoral training schemes, including regular progress reviews and career development plans. Encourage participation in the dissemination of results, and understanding of the wider implications and applications of the research. 7. Use results as part of our regular engagement with non-academic audiences, e.g. local interest groups, schools, local and national shows, science showcases, media. 8. Involve school children and undergraduate students in a practical sense (visits, websites providing teaching resources, blogging and laboratory summer secondments for high school students and undergraduates). 9. Seek opportunities to inform the work of UN agencies and DFID (UK) in the developing world, and the CGIAR international network of germplasm repositories and strategic regional research.