Collaborative Research: Improving plant productivity and models of carbon exchange by resolving mechanisms of excess carbon release in photorespiration

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During photosynthesis, plants use energy from sunlight to convert carbon dioxide from the atmosphere into biomass. This biomass includes the food, fiber and fuel required by humans and other life on this planet. During this conversion, the initial step of photosynthesis can react with atmospheric oxygen instead of carbon dioxide, which produces compounds that must be recycled. This recycling process, called photorespiration, requires large percentages of the plant’s energy reserves and releases carbon dioxide, thereby reducing plant growth and productivity. Photorespiration is affected by environmental conditions, increasing relative to photosynthesis as temperature rises. This research project explores the temperature response of photorespiration to determine how it will respond under future climates and seeking strategies to improve its efficiency. Findings from this proposal will be integrated into education activities and disseminated widely. Diverse students will be engaged via a research collaboration with a primary undergraduate institution serving under-represented students. Additionally, the potential for this work to improve crop productivity and the importance of models in plant biology will be disseminated by continuing Sounds of Science performances. The Sounds of Science is a unique collaboration where composers create music from research data provided by a plant scientist. Presentations where the investigators present an overview of the research and the compositions are performed will be recorded in partnership with local public media and have the potential to reach a public audience of ~500,000 Michigan residents.Photorespiration is the second largest metabolic flux of carbon in an illuminated leaf and occurs when rubisco, the initial enzyme of carbon fixation, binds with oxygen instead of carbon dioxide and produces a molecule that must be recycled. Photorespiration recycles this molecule into Calvin-Benson cycle intermediates at the great cost of carbon. Understanding the mechanisms of carbon dioxide release during photorespiration is critical for predicting plant responses to climate change and potentially engineering plants with improved carbon assimilation and productivity. When temperature increases, photorespiration releases even more carbon dioxide per rubisco oxygenation, but the mechanism of this increase is unknown. The objective of this proposal is to resolve the mechanisms of this excess carbon dioxide release at high temperatures using an innovative combination of metabolic modeling, in vivo gas exchange, and isotopic labeling approaches. The central hypothesis of this proposal is that excess carbon dioxide release occurs from photorespiration at elevated temperatures when intermediates react non-enzymatically in the peroxisome with hydrogen peroxide produced from photorespiration. This hypothesis assumes that under ambient temperatures hydrogen peroxide is efficiently detoxified by the enzyme catalase, but under elevated temperatures catalase is unable to remove hydrogen peroxide quickly enough to minimize non-enzymatic decarboxylation reactions. The results of this project will reach across disciplinary boundaries with the strong potential to improve earth-system models of carbon cycling and to identify key traits for adapting photosynthesis to real-world growing conditions.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.