All organisms require inorganic phosphate (Pi) as a key component of nucleic acids, phosphorylated sugars, phospholipids, and phosphate-containing cofactors. Pi is also a participant in signal transduction cascades, and a regulator of many enzyme activities through phosphorylation. Soils generally contain limited amounts of Pi in forms available for uptake by plant roots. Phosphate fertilizers have been used on a mass scale to combat limited crop productivity caused by low Pi availability, but raw materials to produce those fertilizers are expected to soon run out. In addition, over-fertilization of soils has caused environmental damage. Thus, plants with improved phosphate use efficiency would benefit the society by enabling a more productive agriculture while protecting the environment. The proposed study is expected to advance the knowledge of phosphate metabolism, needed to create such plants. The objective of this application is to biochemically characterize a set of phosphatases from Arabidopsis, and to uncover their roles in homeostasis, which refers to the ability to maintain an internal equilibrium by adjusting physiological processes. The project will test the central hypothesis that these enzymes are cytosolic phosphatases that participate in adjusting cellular levels of Pi and organic phosphoesters in response to developmental programs and external stimuli in plants. The project will test this hypothesis by (1) determining biochemical properties, subcellular localization, and expression patterns of these enzymes; and (2) determining the roles of these enzymes in phosphate homeostasis in plants using genetic approaches. The expected outcome of this study is knowledge of the contributions of cytosolic phosphatases to the overall homeostasis of Pi and organic phosphoesters, which is an uninvestigated aspect of phosphate metabolism in plants. This knowledge is expected to have a significant impact on the overall understanding of the metabolism of Pi and organic phosphoesters because the knowledge of how individual enzymes on metabolic pathways participate in regulating intra-cellular pool sizes of Pi and organic phosphoesters is particularly scarce, and is lagging behind that of the roles of signal transduction networks and transporters. The knowledge gained in this study is expected to be relevant to future attempts at optimizing phosphate use by plant tissues and organs, which would be beneficial because phosphate is a limiting nutrient added during fertilization, and we are expected to run out of the phosphate rock used to manufacture the fertilizer supplies in as little as 50 years. Reduced use of phosphate fertilizers in agriculture would also benefit the environment by reducing pollution.
Participation in this project will provide an opportunity for multidisciplinary training of postdoctoral research associates, graduate, and undergraduate students in plant biochemistry, molecular biology, and metabolism. A strong effort will be made to recruit members of underrepresented groups into the postdoctoral, graduate, and undergraduate student positions. An Associate Professor of Biology at Pacific Lutheran University, a predominantly undergraduate training institution, will participate in the project and apply the new knowledge gained towards updating and developing courses she teaches, and towards helping the participating undergraduate students from Pacific Lutheran University continue some of their research at their home institution, thus directly benefiting a larger group of undergraduate students.
