CAREER: Structural Discovery of Super-Complexes Regulating Energy Flow in Photosynthesis

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Oxygenic photosynthesis sustain life on earth by producing oxygen and providing energy for carbon fixation. Increased human population constantly challenges food and energy supplies thus requiring continued innovation to increase the productivity of photosynthesis in multiple ways. This research project will discover how plants direct light energy absorbed in leaves between two different energetic routes. The outcomes of these two routes, which are called linear and cyclic electron flow, produces different energy carries within plant cells. These energy carries are utilized differentially under different conditions and the balance between them is paramount for plant growth and adaptation. The project aims to discover new components and mechanisms that direct this decision using structural biology and protein engineering approaches. An additional goal of the project is to obtain molecular level images of these routing mechanisms in plants that utilize a special form of photosynthesis called C4 photosynthesis. C4 photosynthesis is employed by some of the most important crop species on the planet, Corn, Sugarcane and Sorghum, and confers to these plants many of the advantages that make them such successful crops, for example, improved water usage and higher photosynthetic efficiency. The project will use Sorghum, a plant better adapted to warm and dry conditions then Corn, as a platform to discover components and mechanisms that control electron flow and may be responsible for some of Sorghum’s unique properties. To improve accessibility to the project’s scientific results and to structural biology in general, scientifically accurate virtual reality scenes will be developed based on the project results. These will be used in basic biochemistry courses and made publicly available. A summer research internship will be offered to veterans to actively participate in this research project to enable exploration of research as career path. Our ability to control and manipulate photosynthesis is severely limited. The long-term goal of the project is to develop a high-level understanding of the function of photosynthetic supercomplexes together with the ability to manipulate their properties in photosynthetic organisms. To achieve this, the project will discover new structures of the photosystem I (PSI) complex in eukaryotes. PSI is one of the most complicated assemblies in nature. Like many large cellular structures, PSI interacts with cellular factors to carry distinct functions, a fact which is still not manifested in our structural description of PSI. Electron flow in photosynthesis follows two main modes, linear or cyclic electron flow (LEF or CEF respectively). By balancing these two pathways, photosynthetic organisms adapt the output of the photosynthetic machinery to cellular needs. The potential for engineering photosynthetic organisms to achieve higher productivity and to synthesize specific chemicals is great but requires changing the basic energy requirements from this machinery. This proposal tackles this issue using cryo-EM supplemented with functional analysis to discover supercomplexes adjusting energy flow around PSI. By determining high-resolution structures of these complexes our mechanistic understanding of the basic systems controlling electron flow modes in photosynthesis will greatly improve. This project is funded by the Molecular Biophysics Cluster in the Division of Molecular and Cellular Biosciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.