C(4) photosynthesis in C(3) rice: a theoretical analysis of biochemical and anatomical factors

Engineering C(4) 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(4) metabolic cycle into a C(3) leaf structure and without removing the C(3) 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(3) rice leaf. Our results show that integrating a C(4) metabolic pathway into rice leaves with a C(3) metabolism and mesophyll structure may lead to an improved photosynthesis under current ambient CO(2) concentration. We analysed a number of physiological factors that influence the CO(2) 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(3) and C(4) cycles. Among these, partitioning of energy between C(3) and C(4) photosynthesis and the partitioning of Rubisco between mesophyll and bundle‐sheath cells are decisive factors controlling photosynthetic efficiency in an engineered C(3)–C(4) leaf. The implications of the results for the sequence of C(4) evolution are also discussed.