Allan Showalter, Ph.D.

     Research in my lab is directed at elucidating the structure, expression, and function of the superfamily of hydroxyproline-rich glycoproteins (HRGPs) found in plant cell walls.  These proteins represent the major protein components of plant cell walls and include the extensins, arabinogalactan proteins, and solanaceous lectins. Using molecular biology, we have isolated and characterized a number of cDNA and genomic clones encoding these cell wall proteins. Moreover, we have used these clones as molecular probes to examine the regulated expression of these genes during development and in response to various stress conditions such as wounding, pathogen infection, and drought.  Biochemical studies are also underway to determine the molecular interactions which these proteins undergo once deposited in the cell wall. Current efforts to express these HRGP genes in transgenic plants is underway in order to elucidate their expression, molecular interactions, and function.

     Another project in the lab involves examining the molecular adaptations of halophytes to saline environments. Here, Atiplex triangularis, a plant that thrives in saline environments, is being examined with respect to its physiological and molecular responses to growth under various salt concentrations. We are particularly interested in the role which glycinebetaine plays as a osmoprotectant as well as the role of plant cell wall proteins in salt tolerance. Consequently, we are elucidating the pattern of cell wall protein gene expression and cloning the genes which encode the enzymes for the synthesis of glycinebetaine for the purpose of genetically engineering crop plants to survive in saline soils.

Selected References:

• Showalter A.M. (2001) Introduction: plant cell wall proteins. Cellular and Molecular Life Sciences, in press.

• Showalter A.M. (2001) Arabinogalactan-proteins: structure, expression, and function. Cellular and Molecular Life Sciences, in press.

• Lu, H., M. Chen, and A.M. Showalter (2001) Developmental expression and perturbation of arabinogalactan-proteins during seed germination and seedling growth in tomato.  Physiologia Plantarum 112, 442-450.

• Stratford, S., W. Barnes, D. L. Hohorst, J. G. Sagert, R. Cotter, A. Golubiewski, A. M. Showalter, S. McCormick, and P. Bedinger (2001) A leucine-rich repeat region is conserved in pollen extensin-like (Pex) genes in monocots and dicots.  Plant Mol. Biol. 46, 43-56.

• Khan, M.A., I. A. Ungar, and A. M. Showalter (2000) Effects of sodium chloride treatments on growth and ion accumulation of the halophyte Haloxylon recurvum.  Communications in Soil Science and Plant Analysis 31, 2763-2774.

• Showalter, A. M., M. Gao, M. J. Kieliszewski, and D. T. A. Lamport (2000) Characterization and localization of a novel tomato arabinogalactan-protein (LeAGP-1) and the involvement of arabinogalactan-proteins in programmed cell death.  In Cell and Developmental Biology of Arabinogalactan-Proteins, (E. A. Nothnagel, A. Bacic, and A. E. Clarke, eds.), Kluwer Academic/Plenum Publishers: New York, pp. 61-70.

• Khan, M. A., I. A. Ungar, and A. M. Showalter (2000) The effect of salinity on the growth, water status, and ion content of a leaf succulent perennial halophyte, Suaeda fruticosa (L.) Forssk.  Journal of Arid Environments 45, 73-84.

• Khan, M. A., I. A. Ungar, and A. M. Showalter (2000) Effects of salinity on growth, water relations and ion accumulation of the subtropical perennial halophyte, Atriplex griffithii Moq. var. stocksii.  Annals of Botany 85, 225-232.

• Gao, M. and A. M. Showalter (2000) Immunolocalization of LeAGP-1, a modular arabinogalactan-protein, reveals its developmentally regulated expression in tomato.  Planta 210, 865-874.