Using synthetic biology approaches to limit photorespiration in rice

Rice productivity is constrained by the limited efficiency of C3 photosynthesis, particularly photorespiration. This thesis explores how synthetic biology can redesign photorespiratory and carbon-fixation pathways to improve photosynthesis, resource-use efficiency, and grain yield in rice. Four engineering strategies were investigated: carbon-conserving photorespiratory bypasses, a carbon-positive photorespiratory bypass, a facultative CAM-like pathway, and energy-efficient single-cell C4-like modules. Together, these approaches increased photosynthetic performance, biomass accumulation, and grain yield through distinct metabolic mechanisms, including carbon conservation, coupling of carbon and nitrogen metabolism, carbon-positive assimilation, temporal reorganisation of carbon fixation, and optimisation of C4 energy use. The results further show that improved leaf photosynthesis alone does not determine crop productivity. Successful photosynthetic engineering requires coordinated changes in whole-plant carbon allocation, nitrogen use, source–sink relationships, and reproductive development. These findings provide new strategies and design principles for developing higher-yielding rice through synthetic biology.