Advances in biotechnological strategies for improving photosynthetic productivity in C3 and C4 plants: falls and rises

Demand for agricultural products continues to rise. Conventional breeding, together with fertilizers, pesticides, and herbicides, has largely exhausted its potential to deliver further major gains in crop productivity. A growing body of research indicates that the next increase in yield potential will depend on genetic engineering. This review surveys current biotechnological strategies for improving the productivity of C3 and C4 crops, including engineering of mesophyll conductance, the light-dependent and dark reactions of photosynthesis, introduction of photorespiratory bypass pathways, and incorporation of CO2-concentrating mechanisms from C4 plants, cyanobacteria, and algae into C3 plants. We discuss approaches that have improved yield, those that have produced detrimental effects, and those that remain controversial or in the development stage. We also consider why some gene-integration strategies might have failed and how current research is addressing the main obstacles to creating crops with higher photosynthetic potential.