Description Of Research
Although plants are photoautotrophic organisms, they are composed of many heterotrophic tissue systems, such as roots, flowers, seeds, and developing leaves, that depend on carbon and nitrogen import for growth and development. In general, sucrose and amino acids are transported to the heterotrophic cells from mature leaves. This process is known as assimilate partitioning and it is a fundamental activity that allows plants to function as multicellular organisms.
My laboratory provided the first biochemical and molecular descriptions of several plant sugar and amino acid transport systems that are key contributors to resource allocation within cells and between organs. We initially described these transporters using an in vitro biochemical assay that allowed us to define the transport properties and bioenergetics of these important carriers. To identify the genes encoding the plant's sugar and amino transporters, we used functional complementation of yeast transport mutants with plant cDNA expression libraries (PNAS 90:7441-7445). The yeast system is very useful because it allows us measure key transport properties and protein structure/function relationships when plant transport proteins expressed in yeast cells (PNAS 95:9025-9030).
The unifying theme of our research today is understanding how plants regulate resource allocation between "source and sink" tissues. To tackle this complex question, we are using genetic and biochemical strategies to identify the signal transduction pathways that regulate assimilate partitioning. We discovered a unique sucrose-mediated signal transduction pathway that regulates the expression and protein abundance of the sucrose transporter that is responsible for phloem loading (PNAS 95:4784-4788; PNAS 99:10876-10880). In complementary research, we are looking at environmental signals that control the expression of plant amino acid transporters using microarrays and other genomic tools. In addition to advancing our understanding of fundamental process in plant growth and development, the results of these investigations will allow us to develop rational strategies to improve crop productivity and enhance nutritional value.
Representative Publications
Harrington GN and Bush DR 2003. The bifunctional role of hexokinase in metabolism and glucose signaling. Plant Cell 15: 2493-2496
Ransom-Hodgkins W, MW Vaughn, and DR Bush 2003. Protein phosphorylation mediates a key step in sucrose-regulation of the expression and transport activity of a beet proton-sucrose symporter. Planta 217:483-489
Vaughn MW, GN. Harrington, and DR Bush 2002. Sucrose-mediated transcriptional regulation of sucrose symporter activity in the phloem. Proc. Natl. Acad. Sci. USA 99:10876-10880
Coruzzi G and Bush DR 2001. Nitrogen and carbon nutrient and metabolite signaling in plants. Plant Physiol 125: 65-68
Ortiz-Lopez A, H-C Chang, and DR Bush 2000. Amino acid transporters in plants. Biochimica et Biophysica Acta - Biomembranes 1465:275-280
Bush DR 1999. Sugar transporters in plant biology. Current Opinion in Plant Biol. 2:187-191
Chiou TJ and DR Bush 1998. Sucrose is a signal molecule in assimilate partitioning. Proc. Natl. Acad. Sci. USA 95:4784-4788
Chang H-C and DR Bush 1997. Topology of NAT2: a prototypical example of a new family of amino acid transporters. J. Biol. Chem. 272: 30552-30557
Bush DR 1993. Proton-coupled sugar and amino acid transporters in plants. Annu Rev Plant Physiol and Plant Mol Biol 44:513-542
Hsu L-C, TJ Chiou, L Chen, and DR Bush 1993. Cloning a plant amino acid transporter by functional complementation of a yeast amino acid transport mutant. Proc. Natl. Acad. Sci. USA 90:7441-7445
