RUI: Assessing C4-pathway regulation by the pyruvate phosphate dikinase regulatory protein in maize leaves

Minnesota State University Moorhead, Moorhead MN

Investigators

Abstract

Almost all plants fix CO2 into carbohydrate using an ancient photosynthetic process termed C3 photosynthesis (i.e., C3 plants). A subset of plants utilize a more efficient photosynthetic process termed C4 photosynthesis (i.e., C4 plants). In open sunny environments the rate of CO2 fixation, biomass accumulation, and grain yield in C4 plants is nearly twice that of C3 plants. The increased photosynthetic performance of C4 versus C3 plants is due in part to the evolution of an additional set of photosynthetic CO2 fixation enzymes referred to as the C4 pathway. Despite the inherently higher productivity of C4 versus C3 plants, there are only four agronomically important C4 crop species: maize, Sorghum, sugar cane, and switch grass. All other crop species (e.g., rice, soybean, wheat) are C3 plants. Thus an ongoing research goal of plant scientists is to breed or engineer C4 photosynthesis into C3 crop plants for improving yields. Efforts to date have fallen short in part because of the lack of understanding on how the C4 pathway is controlled in leaves for optimizing use of available sunlight. The ultimate aim of this project is to elucidate how such regulation works. A first step in this endeavor, and the goal of this one-year project, is to develop maize plants that are deficient in two interrelated light-responsive C4 pathway enzymes, pyruvate phosphate dikinase (PPDK) and the PPDK regulatory protein (RP). It is hypothesized that these enzymes control the rate of the CO2 fixation by the C4 pathway in response to sunlight. Using RNA interference, a genetic engineering method, stable lines of maize plants will be isolated with reduced levels of PPDK or RP enzyme. These plants will be subsequently assessed for photosynthetic performance. From these analyses, an accurate picture of how PPDK and RP confer sunlight-responsive C4 pathway regulation is expected to emerge. This knowledge will be critical for projects now underway that seek to introduce a functional C4 pathway into leaves of C3 crop species. A major education and training component of the project is the participation of undergraduate Biochemistry/Biotechnology degree students in fulfillment of their senior thesis research requirement.