Cell specific expression of genes in C4 photosynthesis

By 2050, due to population growth we will need at least 50% more food than today. However, increases in the maximum yield of crops such as rice have plateaued. There are few biological precedents that show that yields can be increased by this order of magnitude, but C4 photosynthesis is one of them. It has therefore been proposed that placing characteristics of C4 photosynthesis into crops that currently use the less efficient C3 pathway should be attempted. Before this is feasible, we need a better basic understanding of how the C4 pathway operates. We have recently identified a region that is shared by multiple genes, and that generates BS specificity in leaves of the C4 plant C. gynandra. This is the first example of cell specificity in C4 leaves being generated by information within coding regions. In addition, this region is already present in orthologous genes from C3 species, and so shows that genes can be directly recruited into cell specific expression in C4 leaves without any change in sequence. We aim to define the nucleotides present in this region that generate BS specificity, to determine the extent to which other genes in the C4 cycle are regulated by elements within their coding regions, and also to define the extent to which genes from C3 species already possess elements that generate M or BS specificity in C4 leaves.

C4 photosynthesis consists of co-ordinated alterations to the biochemistry, cell biology and development of leaves, that, compared to the C3 pathway increase photosynthetic efficiency by 50%. The higher rates of photosynthesis generate faster rates of growth and therefore productivity. By 2050, due to population growth we will need at least 50% more food than today, but increases in the maximum yield of crops such as rice have plateaued. C4 photosynthesis is known to increase yields by this extent, and so introducing the C4 pathway into C3 plants is one possible strategy to increase crop production for the future. A better understanding of basic mechanisms operating in C4 leaves is needed if placing characteristics of C4 photosynthesis into C3 crops is to be feasible. One of the key differences between the leaves of C3 and C4 plants is that photosynthesis is spatially separated between mesophyll and bundle sheath cells of C4 plants. We have identified a region that is shared by multiple genes, and that generates BS specificity in leaves of the C4 plant C. gynandra. This is the first example of cell specificity in C4 leaves being generated by information within coding regions. In addition, this region is already present in orthologous genes from C3 species, and so shows that genes can be directly recruited into cell specific expression in C4 leaves without any change in sequence. We aim to define the nucleotides present in this region that generate BS specificity, to determine the extent to which other genes in the C4 cycle are regulated by elements within their coding regi

Beneficiaries from the research will depend on the timescale over which this is assessed. In the short-term, the international scientific community will benefit from the increase in knowledge relating to the C4 pathway that will be produced from this project. This will include those working on metabolism of C4 photosynthesis, cell biology of the pathway, and transcriptional regulation of C4 networks. Policy makers in IRRI, Governments, and Charitable Foundations will likely be influenced by the data we generate, as it will provide insight into the complexity of the C4 pathway, which currently is of interest in terms of placing in rice to increase yield. This pure science is critical at this time to inform such decisions. In the longer term, the knowledge will be used by the C4 rice consortium in order to determine future directions for the project. For example, it may well be of benefit from an understanding of the extent to which cis elements used to generate cell specific expression are shared between genes, and also the importance of direct recruitment of C3 genes into cell specificity in C4 leaves. If the C4 rice project continues, and it adopted as a strategy to increase yield of rice, then the knowledge gained in this project will likely be important to this, and if C4 rice is made, it would impact on billions of people world wide, by helping to maintain and sustain rice production, and control the cost of production. In addition to increasing yield, C4 rice would have higher nitrogen and water use efficiency, so having environmental benefits. In the long term, the research may impact on the nations the nation's health, wealth or culture, by contributing to future global security and food supply. A stable political climate is more likely in economically developing countries if sufficient food is produced. In addition, if food supply is commensurate with population growth, continued international economic growth is likely, and so exports for the UK will be maintained and enhanced. This would increase quality of life, health and creative output. Economic impacts of generating C4 rice are estimated to be 100 billion per annum, and the timescale is thought to be around twenty years. Staff working on the project will develop sate of the art skills in molecular biology, plant transformation, and work with important crop plants. All of these are growing skills that will be required in a competitive knowledge based economy. The proposed research project will be managed to engage users and beneficiaries and increase the likelihood of impacts. This will include communication and engagement with the scientific community be presentations at conferences, publication in peer-reviewed journals, and results of interest to the public will be made available via IRRI's public information service. Collaboration arrangements are strong as all the major labs in the world are part of the C4 rice consortium managed by IRRI. Exploitation would be managed by IRRI as and when appropriate. I have considerable experience in this area of science, being internationally recognised for my work on C4 photosynthesis. (International Photosynthesis Calvin Prize, 2007; named by Nature in 2008, and advisory board member to IRRI on C4 rice.