Dr. Howard D. Grimes
Our laboratory is primarily interested in the biochemistry and regulation of assimilate partitioning for both carbon and nitrogen. Within this broad umbrella, we have projects specifically aimed at
1) metabolic engineering of sucrose metabolism
2) identification and characterization of sucrose transport proteins and protein-protein interactions
3) role of lipoxygenases as vegetative storage proteins, and
4) biochemistry of lipoxygenase function in carbon and nitrogen mobilization.
Central to understanding carbon partitioning and its regulation is the biochemical dissection of the individual transport steps along this pathway. Sucrose uptake across the plasma membrane, long-distance transport, and deposition into sink tissues offers several distinct sites to address carbon flux management. Work focuses on the integral, sucrose/H+ symporters (SUTs) at the plasma membrane of plant cells.
Site-directed mutagenesis and domain swapping have been used to modify the transport properties of these proteins and modification of the promoter elements allows control both spatial and temporal aspects of gene expression. Hence, discrete points in the carbon flux pathway can be altered in a highly specific manner. Recently, we have identified a binding protein associated with the cytosolic loop of the sucrose transporter. Apparently this protein-protein interaction leads to the formation of sucrose "metabolons" that involve both plasma membrane transporters and cytoskeleton-linked sucrose metabolizing enzymes.
The reallocation of carbon and nitrogen from the vegetative organs to the developing seeds is an especially important component of plant productivity. Our laboratory discovered that a specific lipoxygenase isoform functions as "vegetative storage protein" and accumulates in the vacuole of a unique cell layer in leaves. More recently we have shown that these plant vacuoles are able to convert between lytic and storage functional states. This latter discovery has propelled our research into the mechanistic understanding of selective degradation of proteins in plant cells.
Youn, B., G.E. Sellhorn, R.J. Mirchel, B.J. Gaffney, H.D. Grimes, and C. Kang. 2006. Crystal Structures of Vegetative Soybean Lipoxygenase VLX-B and VLX-D, and Comparisons with Seed Isoforms, LOX-1 and LOX-3. Proteins: structure, function, and bioinformatics (in press).
Murphy, K.A., R.A. Kuhle, A.M. Fischer, A.A. Anterola, and H.D. Grimes. 2005. The Functional Status of the Paraveinal Mesophyll Vacuole Changes in Response to Altered Metabolic Conditions in Soybean Leaves. Functional Plant Biology 32:335-344.
Elmer A.M., W.S. Chao, and H.D. Grimes. 2003. Protein Sorting and Expression of a Unique Soybean Cotyledon Protein, GmSBP, Destined for the Protein Storage Vacuole. Plant Molecular Biology. 52:1089-1106.
Aldape, M.J, A.M. Elmer, W.S. Chao, and H.D. Grimes. 2003. The Identification and Characterization of a Sucrose Transporter Isolated from the Developing Cotyledons of Soybean. Arch. Biochem. Biophys. 409:243-250.
Fisher, A.J., H.D. Grimes, and R. Fall. 2003. The Biochemical Origin of Pentenol Emissions from Wounded Leaves. Phytochem. 62:159-163.
Fuller, M., Weichert, H., Fischer, A., Feussner, I., and H.D. Grimes. 2001. Activity of Soybean Lipoxygenase Isoforms Against Esterified Fatty Acids Indicates Functional Specificity. Arch. Biochem. Biophys. 388:146-154.
Dubbs, W.E. and H.D. Grimes. 2000. The Mid-PericarpCell Layer in Soybean Pod Walls is a Multicellular Compartment Enriched in Specific Lipoxygenase Isoforms. Plant Physiol. 123:1281-1288.
Dubbs, W.E. and H.D. Grimes. 2000. Specific Lipoxygenase Isoforms Accumulate in Distinct Regions of Soybean Pod Walls and Mark a Unique Cell Layer. Plant Physiol. 123:1269-1279.
Fischer, A.M., Dubbs, W.E., Baker, R.A., M.A. Fuller, Stephenson, L.S., and H.D. Grimes. 1999. Protein Dynamics, Activity, and Cellular Localization of Soybean Lipoxygenases Indicate Distinct Functional Roles for Individual Isoforms. Plant Journal 19:543-554.
Jauh, G-Y., Fischer, A.M., Grimes, H.D., Ryan, C.A. and Rogers, J.C. 1998. d-Tonoplast Intrinsic Protein Defines Unique Plant Vacuole Functions. Proc. Natl. Acad. Sci. USA 95:12995-12999.
Stephenson, L.C., Bunker, T.W., Dubbs, W.E. and Grimes, H.D. 1998. Differential Expression and Cellular Localization of Nitrogen-Responsive Lipoxygenases in Soybean. Plant Physiology 116:923-933.