CAREER: Glycogen metabolism kick-starts photosynthesis in cyanobacteria

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Life on Earth depends on photosynthesis to harvest solar energy. During the day, plants and other photosynthetic organisms use solar energy to fix carbon dioxide and store excess carbon as carbon polymers such as starch or glycogen. At night, these storage carbons are broken down as the energy source for dark survival. The dark-to-light transition represents a universal environmental stress for photosynthetic lifeforms. For example, many metabolites necessary for photosynthetic reactions upon light exposure are limited or depleted due to metabolic reactions conducted in dark. It is important for photosynthetic organisms to have a mechanism in place to cope with this stress and ensure healthy photosynthetic performance upon exposure to light. How photosynthetic organisms achieve this dark-to-light transitions remains unclear. This research project applies cutting-edge biochemical and systems biology approaches to dissect the molecular mechanisms that allow this dark to light transition to occur in a model photosynthetic blue green alga. Knowledge gained from this research will how storage polymers like glycogen pave the way for carbon dioxide fixation to occur during the dark to light transition and eventually lead to ways to improve photosynthetic efficiency for crop productions. The research project also provides training opportunities for one postdoctoral researcher, one graduate student, and several undergraduate students. Components of this research are also integrated in a cluster education program as well as in the form of a special topics course on Synthetic Biology to broaden the training opportunity and strengthen scientific literacy for both undergraduate and graduate students. Cyanobacteria experience drastic metabolic changes under daily light/dark cycles. The smooth metabolic transition from dark to light is crucial for healthy photosynthetic performance and the overall fitness of phototrophs. It is known that glycogen metabolism is involved in supporting the initiation of the Calvin-Benson-Bassham (CBB) cycle reactions during dark-to-light transitions in the cyanobacterium Synechococcus elongatus PCC 7942. However, the molecular mechanisms of how glycogen metabolism supports photosynthesis are not clear. This project applies proteomics, metabolomics, metabolic flux analysis, and photochemical analyses to characterize the coping mechanism of cyanobacteria for the dark-to-light transition stress. The research activities will illustrate the status of a stalled CBB cycle, and understand how glycogen metabolism helps replenish and restart carbon fixation reactions, as well as protecting Photosystem I from photoinhibition during dark-to-light transitions. Discoveries from the research will significantly advance the understanding on a fundamental mechanism employed by photosynthetic lifeforms to cope with the dark-to-light transition stress and further our knowledge on energy balance between photosynthetic light reactions and carbon fixation. Results from the study also benefit photosynthesis redesign research in the field of synthetic biology for sustainable food supply.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.