RUI: Glucan Phosphatases and Regulation of Transitory Starch Metabolism

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The goal of this research project is to understand how starch breakdown in plants is regulated at the protein level. Starch is the major carbon storage form of plants, a main source of calories in the human diet, and an important raw material for various industrial applications. Despite the importance of starch in biological systems and in human society, our understanding of the regulation of starch metabolism is surprisingly limited and far from complete. Transitory starch, a primary product of photosynthesis, accumulates in plant leaves during the day, and is degraded at night to provide energy for cellular activities and plant growth. Starch degradation is a complex process that requires the combined activity of several protein families including glucan phosphatases, glucan dikinases, and amylases. However, there are many unanswered questions regarding how these proteins specifically contribute to starch degradation. This research project will investigate the role that glucan phosphatases play in initiating and regulating transitory starch degradation. A complete understanding of the molecular events that control starch degradation is necessary to define novel strategies to improve starch yields in crops, a raw material for biofuel and various industrial and agricultural applications. Undergraduate researchers working on this project, some of whom will be from underrepresented and minority populations, will be provided the opportunity to engage in structural biochemistry and metabolomics research, travel to national conferences to present their work, and collaborate closely with experts in the field. Thus, this project will provide mentorship and training for the next generation of scientists and help retain both underserved and underrepresented students in the sciences. This research will also contribute to biochemistry undergraduate education through the design of a project-based laboratory course. Overall, the project represents a robust combination of advancing foundational research, improving undergraduate education, and positively impacting future agricultural and industrial applications.Starch is an insoluble polymer of glucose. Phosphorylation of the starch outer glucosyl residues by glucan dikinases makes the starch granule partially water soluble and accessible to starch degrading enzymes such as -amylases. The subsequent removal of phosphate groups by glucan phosphatases is necessary for complete starch breakdown. By employing a variety of structural, biophysical, and biochemical techniques, the project will investigate the various steps in starch dephosphorylation and its undefined roles in regulating starch degradation. Specifically, the project aims to understand 1) the mechanisms by which glucan phosphatases contribute to the regulation of starch degradation; 2) the structural basis of glucan dephosphorylation at the starch granule; and 3) the critical roles of starch dephosphorylation in diurnal starch metabolism. By employing metabolomics, the project will explore the direct and indirect roles of starch phosphorylation in starch metabolism under abiotic stress. The results of this research project will help close the knowledge gap in understanding the roles and regulatory mechanisms of the glucan phosphatase family of enzymes.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.