Roles of subcellular amino acid transporters in source and sink function

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Plants require large amounts of nitrogen for growth and development. The nitrogen is generally taken up from the soil and then used to produce amino acids. These amino acids play highly diverse and essential roles in plants. They are the basic units of proteins and enzymes, and thereby fundamental to cellular structure and metabolism. Moreover, they are crucial for the synthesis of a large variety of compounds, such as chlorophyll, vitamins and other products needed for plant function as well as for human nutrition. In addition, amino acids serve as signaling molecules triggering physiological processes including plant responses to environmental stresses, and they present the main long-distance nitrogen forms transported to seeds for growth. This project intends to provide pioneering insights on the mechanisms of amino acid partitioning within the cell and their importance for leaf and seed development, and plant survival. It is expected to discover strategies on how amino acid movement can be manipulated to alter nitrogen supply into specific metabolic and transport pathways, with consequences for plant growth, productivity and responses to environmental stresses. The activities will further promote student teaching and training, and foster effective integration of plant biology education and research.A fundamental process in plants is the selective partitioning of amino acids among different organelles, cells, tissues and organs. Various transport mechanisms must exist within the cell to accommodate their directional transport, and these mechanisms must be coordinated and regulated at different levels to achieve normal physiological functions. In Arabidopsis, more than 100 putative amino acid transporters have been identified but physiological functions in nitrogen transport have only been demonstrated for relatively few transporters, and these are mainly plasma membrane-localized. This project intends to identify novel subcellular amino acid transporters and resolve their substrate specificity and mechanisms of transport. Plants, in which the transporters are knocked-out, knocked-down or overexpressed will be analyzed using molecular, cell-biological and biochemical approaches to unravel the physiological functions of the membrane proteins and their importance for plant growth and development. Finally, amino acids have been shown to play important roles in plant performance under environmental stress conditions. The transporter mutants or overexpressors will be exposed to abiotic stresses and their responses will be examined. Together, this project will help to resolve the function of intracellular membrane transporters and their role in nitrogen partitioning between cellular compartments to promote source leaf function, and in long distance amino acid transport in support of seed development. Evidence will be found on how specific amino acid transporters interconnect nitrogen and carbon metabolism, and other biochemical pathways, and if and how they influence plant responses to abiotic stress.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.