Engineering for Robust Photorespiratory Bypass to Improve Photosynthesis and Crop Production Under Field Conditions

Worldwide nearly 1 billion people are affected by hunger every day. As climate changes globally and human population increases, traditional methods of crop improvement have become less effective in adapting and improving agricultural production. In C3 crops such as wheat and rice approximately 25% of the fixed carbon dioxide is lost to photorespiration. Photorespiration is an energy expensive metabolic pathway that recycles toxic compounds produced by RubisCO oxygenation reactions. Reducing photorespiratory yield losses by 5% (i.e., to 31% for soybean and 15% for wheat) would be worth ~$500 million annually in the United States. Although photorespiration is tied to other important metabolic functions, the benefit of improving its efficiency appears to outweigh any potential secondary disadvantages. Synthetic biology has provided new opportunities in altering photorespiratory metabolism to improve photosynthetic efficiency. Indeed metabolic bypasses to photorespiration have been generated and have demonstrated improvements in growth. Using a synthetic biology approach we have assembled a series of multigene constructs that contain alternate metabolic pathways to bypass photorespiration. In addition, we designed a screen based approach to test a range of standardized parts (promoters, terminators) in the model plant Nicotiana tabacum. We have successfully transformed in large multigene constructs and have demonstrated detectable gene expression and improvements in biomass in replicated greenhouse and field trails. Determining robust photorespiratory bypass constructs can provide insight into next generation crops and our utilization of standard parts provide a new tool kit for plant synthetic biology to engineer improvements in photosynthetic efficiency.