Photorespiration can account for yield losses of 25-50% in C3 plants, which include rice, wheat and soybean, three of the top four crops in terms of global grain production. Photorespiration occurs because oxygen and carbon dioxide (CO2) compete for the same acceptor molecule in photosynthesis. The process can be very simply inhibited by increasing the concentration of CO2. When CO2 is increased artificially in greenhouses or in open fields, very significant yield increases are obtained. However, artificially elevating CO2 over millions of acres of fields is not feasible. Some cyanobacteria solve this problem by confining the fixation of carbon to a structure termed a carboxysome, where localization of specific enzymes cause a concentration of CO2. Although chloroplasts, which contain the photosynthetic machinery of crops, lack carboxysomes, they evolved from cyanobacteria, which were symbiotically recruited into the ancestors of todays plants and crops. This research project will provide the foundation for a synthetic biology approach in which carboxysomes will be engineered into the chloroplasts of crop plants to enhance photosynthesis. Optimization will involve manipulating a model plant that is readily transformable and the development of an in silico model of the system to evaluate the use of different proteins and the minimal system that is needed. A multidisciplinary approach will be implemented through collaboration of four research groups, each contributing complementary expertise: carboxysome genetics and assembly (Berkeley), chloroplast and nuclear transformation (Cornell), photosynthetic systems modelling (Illinois) and physiological and biochemical characterization of the whole plant (Rothamsted, Cornell and Illinois). The project will allow postdoctoral and undergraduate trainees to gain experience in an international collaborative project (All). Research resources for comparing plant and bacterial genes will be developed for use in undergraduate education (Berkeley).
