Recent activities to improve photosynthetic performance in crop plants have focused primarily on C3 photosynthesis where there are clear identified targets such as improving Rubisco kinetics, installation of a CO2 concentrating mechanism and alleviating limitations in chloroplast electron transport. However, C4 plants that utilise the C4 photosynthetic pathway also play a key role in world agriculture. For example, C4 crops such as maize and sorghum are major contributors to both first and third world food production and the C4 grasses sugarcane, miscanthus and switch grass are major plant sources of bioenergy. Strategies to manipulate and enhance C4 photosynthesis thus have potential for major agricultural impacts.
The C4 photosynthetic pathway is a biochemical CO2 concentrating mechanism that requires the coordinated functioning of mesophyll and bundle sheath cells of leaves, and species have evolved a complex blend of anatomy and biochemistry to achieve this.
We have used a mathematical model of C4 photosynthesis to explore possible targets for improving C4 photosynthesis, and we are using the model monocot C4 species Setaria viridis (green foxtail millet) to generate transgenic plants with altered C4 photosynthetic metabolism. In our presentation we look at a number of targets we have identified. These include the regulation of chloroplast electron transport and the role of CO2 diffusion at the intercellular airspace – mesophyll and mesophyll-bundle sheath interface in C4 photosynthesis.