This Small Business Technology Transfer (STTR) Phase I project proposes to improve intrinsic crop yield through metabolic engineering of photosynthetic pathways. Genes encoding five rate-limiting enzymes for photosynthesis and starch synthesis will be co-expressed constitutively or in a cell-specific manner in a model C4 plant species. Multiple metabolic pathways will be altered to simultaneously relieve multiple rate-limiting steps for carbon assimilation. The effects of enzyme accumulation on photosynthetic performance, plant growth, and biomass accumulation will be assayed, and optimal combinations of enzymes and relative enzyme levels will be determined. The effects of constitutive enzyme accumulation will be compared with cell-specific enzyme accumulation to determine whether a targeted expression profile can deliver a more substantial improvement in carbon assimilation rates and plant growth than constitutive enzyme accumulation. The results of this work will identify key rate-limiting enzymes in the photosynthetic machinery, optimal enzyme expression profiles, and optimal enzyme concentrations to improve photosynthetic performance, carbon assimilation, and yield. The broader impact/commercial potential of this project, if successful, will be to identify novel ways to improve crop yields in a range of both food and non-food crops. Photosynthetic engineering for improved carbon assimilation is a promising, but underexplored, method for improving intrinsic crop yield. Traditional plant biotechnology approaches have sought to protect yield, e.g. through insect resistance and herbicide tolerance. Utilizing synthetic biology to engineer primary metabolism and increase intrinsic crop yields will work in tandem with existing yield-protecting technologies. Modeling and initial proof-of-concept studies have confirmed that photosynthetic pathways can be engineered for greater efficiency, resulting in yield improvements. The results of this work will significantly enhance our understanding of the rate-limiting steps of photosynthetic carbon assimilation, providing insight into the most promising reactions and metabolic pathways for these engineering approaches. Translating the results of this Phase I work to crop plants will result in improved crop harvests without expanding the agricultural footprint, translating to enormous commercial benefits to the agricultural, food, and energy sectors.
