Faculty:Allan M. Showalter





Allan M. Showalter
Professor

Ph.D., Rutgers University, 1983
Molecular Biology

Phone: 740.593.1135
Fax: 740.593.1130
Email: showalte@ohio.edu

Showalter Lab & Graduate Students

Courses

  • BIOL 101 (Principles of Biology)
  • PBIO 427/527 (Molecular Genetics)
  • PBIO 450/550 (Biotechnology and Genetic Engineering)
  • MCB 720 (Molecular Biology)
  • MCB 730 (Molecular and Cellular Biology Laboratory)

Departmental Service

  • Promotion and Tenure Committee (Chair)
  • Graduate Committee

Research Program Summary

  • Molecular biology and biochemistry of plant cell wall proteins
    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 the plant cell surface (i.e., the plant cell wall and plasma membrane) and include the extensins, proline-rich proteins, arabinogalactan-proteins, and solanaceous lectins. Using a variety of molecular biology techniques, we have isolated and characterized a number of cDNA and genomic clones encoding these cell surface 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 underway to determine the molecular interactions that these proteins undergo once deposited at the cell surface. Current efforts to alter the expression of these HRGPs in plants using a variety of techniques (antisense RNA, RNA interference, insertional mutagenesis, overexpression, expression of fusion proteins) in transgenic plants is also underway in order to elucidate their expression, molecular interactions, and functions. We have expressed a GFP-arabinogalactan-protein fusion in transgenic plants and used it to demonstrate that this particular arabinogalactan-protein is attached to the plasma membrane via a glycosylphosphatidylinositol (GPI) lipid anchor. We have also established a link between arabinogalactan-proteins and programmed cell death in plants. Our recent work makes use of the genetic model plant, Arabidopsis thaliana, in which we are studying various AGP mutants to elucidate AGP function and also isolating the enzymes (and the genes that encode them) responsible for glycosylating AGPs and other HRGPs. Our research on arabinogalactan-proteins is supported by NSF grants IBN-9727757 and IBN-0110413.
  • Molecular adaptations of halophytes to saline environments
    Another project in the lab involves examining the molecular adaptations of halophytes to saline environments. Here, Atriplex prostrata, 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 an osmoprotectant. Consequently, we have cloned the genes that encode the pathway for the synthesis of glycinebetaine for the purpose of genetically engineering crop plants to survive in saline soils.

Selected References

  • Showalter, A. M. (1993) Structure and function of plant cell wall proteins. Plant Cell 5, 9-23. (pdf)

  • Li, S. and A.M. Showalter. 1996. Cloning and developmental/stress-regulated expression of a gene encoding a tomato arabinogalactan protein. Plant Molecular Biology 32, 641-652. (pdf)
  • Wang, L.-W., A.M. Showater, and I.A. Ungar (1997) Effect of salinity on growth, ion content and cell wall chemistry in Atriplex prostrata Boucher.  Amer. J. Bot. 84, 1247-1255. (pdf)
  • Khan, M. A., I. A. Ungar, A. M. Showalter, and H. Dewald (1998) NaCl-induced accumulation of glycinebetaine in four subtropical halophytes from Pakistan.  Physiol. Plant. 102, 487-492. (pdf)
  • Khan, M. A., I. A. Ungar, and A. M. Showalter (1999)  Effects of salinity on growth, ion content, and osmotic relations in Halopyrum mucronatum (L.) Stapf.  J. Plant Nutr. 22, 191-204. (pdf) 
  • Gao, M., M. J. Kieliszewski, D. T. A. Lamport, and A. M. Showalter (1999) Isolation, characterization, and immunolocalization of a novel, modular tomato arabinogalactan-protein corresponding to the LeAGP-1 gene.  Plant J. 18, 43-55. (pdf)
  • Gao, M. and A. M. Showalter (1999) Yariv reagent treatment induces programmed cell death in Arabidopsis cell cultures and implicates arabinogalactan-protein involvement.  Plant J. 19, 321-331. (pdf)
  • 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. (pdf)
  • 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.(pdf)
  • 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.(pdf)
  • 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. (pdf)
  • 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. (pdf)
  • 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. (pdf)
  • 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. (pdf)
  • Showalter A.M. (2001) Arabinogalactan-proteins: structure, expression, and function. Cellular and Molecular Life Sciences 58, 1399-1417. (pdf)
  • Showalter A.M. (2001) Introduction: plant cell wall proteins. Cellular and Molecular Life Sciences 58, 1361-1362. (pdf)
  • Zhao Z., L. Tan, A.M. Showalter, D.T.A. Lamport, and M. Kieliszewski (2002) Tomato LeAGP-1 arabinogalactan-protein purified from transgenic tobacco corroborates the Hyp contiguity hypothesis. Plant Journal 31, 431-444. (pdf)
  • Chaves I., A. Regalado, M. Chen, C. Ricardo and A.M. Showalter (2002) Programmed cell death induced by (b-D-galactosyl)3 Yariv reagent in Nicotiana tabacum BY-2 suspension-cultured cells. Physiologia Plantarum 116, 548-553. (pdf)
  • Sun, W., Z.D. Zhao, M.C. Hare, M.J. Kieliszewski, and A.M. Showalter (2004) Tomato LeAGP-1 is a plasma membrane-bound glycosylphosphatidylinositiol-anchored arabinogalactan-protein. Physiologia Plantarum 120, 319-327. (pdf)
  • Wang, L.-W. and A.M. Showalter (2004) Cloning and salt-induced, ABA-independent expression of choline mono-oxygenase in Atriplex prostrata. Physiologia Plantarum 120, 405-412. (pdf)
  • Sun, W., M. J. Kieliszewski, and A.M. Showalter  (2004) Overexpression of tomato LeAGP-1 arabinogalactan-protein promotes lateral branching and hampers reproductive development. Plant Journal 40, 870-881. (pdf)
  • Sun, W., J. Xu, J. Yang, M. J. Kieliszewski, and A.M. Showalter  (2005) The lysine-rich arabinogalactan-protein subfamily in Arabidopsis: gene expression, glycoprotein purification and biochemical characterization. Plant and Cell Physiology 46, 975-984. (pdf)
  • Khan, M.A., I.A. Ungar, and A.M. Showalter (2005) Salt stimulation and tolerance in an intertidal stem-succulent halophyte. Journal of Plant Nutrition 28, 1365-1374. (pdf)
  • Wang, L.-W., A.M. Showalter, and I.A. Ungar (2005) Effects of intraspecific competition on growth and photosynthesis of Atriplex prostrata. Aquatic Botany 83, 187-192. (pdf)
  • Lamport, D.T.A., M.J. Kieliszewski, and A.M. Showalter (2006) Salt stress upregulates periplasmic arabinogalactan proteins: using salt stress to analyse AGP function. New Phytologist 169, 479–492. (pdf)
  • Sardar, H., J. Yang, and A.M. Showalter (2006) Molecular interactions of arabinogalactan- proteins (AGPs) with cortical microtubules and actin in bright yellow 2 (BY-2) tobacco cultured cells. Plant Physiology 142, 1469-1479. (pdf)

  • Yang J., H. S. Sardar, K. R. McGovern, Y. Zhang, and A. M. Showalter (2007) A lysine-rich arabinogalactan-protein in Arabidopsis is essential for plant growth and development, including cell division and expansion. Plant Journal 49, 629-640. (pdf)

  • Sardar H. and A. M. Showalter (2007) A cellular networking model involving interactions among glycosylphosphatidylinositol (GPI)-anchored plasma membrane arabinogalactan proteins (AGPs), microtubules and F-actin in tobacco BY-2 cells. Plant Signaling and Behavior 2, 8-9. (pdf)

  • Yang J. and A. M. Showalter (2007) Expression and localization of AtAGP18, a lysine-rich arabinogalactan-protein in Arabidopsis. Planta, 226, 169-179. (pdf)

Much of this research was supported by NSF under grants   IBN-0110413 and IBN-9727757; however, "any opinions, findings, and conclusions or recommendations expressed in this material are those of the author (s) and do not necessarily reflect the views of the National Science Foundation."

Research Focus Area

Current or Recent Student Research Projects

  • Isolation and characterization of genes encoding tomato and Arabidopsis arabinogalactan-proteins
  • Molecular interactions and function of LeAGP-1, a modular plasma membrane arabinogalactan-protein in tomato
  • Expression of GFP-LeAGP-1 fusion proteins in transgenic plants for purification and characterization of a native arabinogalactan-protein
  • Cloning and characterization of the betaine aldehyde dehydrogenase and choline monooxygenase genes from the halophyte Atriplex prostrata
  • Programmed cell death in plants and the role of arabinogalactan-proteins in this process
  • A bioinformatics-based approach to the identification, classification, and analysis of genes encoding plant cell wall hydroxyproline-rich glycoproteins (HRGPs)
  • Use of RNA interference and insertional mutagenesis to elucidate the function of arabinogalactan-proteins
  • Microarray analysis of arabinogalactan-protein mutants in Arabidopsis
  • Isolation and characterization of the enzymes (and the genes that encode them) responsible for glycosylating AGPs and other HRGPs

 


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