C photosynthesis in C rice: a theoretical analysis of biochemical and anatomical factors.

Engineering C photosynthesis into rice has been considered a promising strategy to increase photosynthesis and yield. A question that remains to be answered is whether expressing a C metabolic cycle into a C leaf structure and without removing the C background metabolism improves photosynthetic efficiency. To explore this question, we developed a 3D reaction diffusion model of bundle-sheath and connected mesophyll cells in a C rice leaf. Our results show that integrating a C metabolic pathway into rice leaves with a C metabolism and mesophyll structure may lead to an improved photosynthesis under current ambient CO concentration. We analysed a number of physiological factors that influence the CO uptake rate, which include the chloroplast surface area exposed to intercellular air space, bundle-sheath cell wall thickness, bundle-sheath chloroplast envelope permeability, Rubisco concentration and the energy partitioning between C and C cycles. Among these, partitioning of energy between C and C photosynthesis and the partitioning of Rubisco between mesophyll and bundle-sheath cells are decisive factors controlling photosynthetic efficiency in an engineered C -C leaf. The implications of the results for the sequence of C evolution are also discussed.