Distinguished Research Professor of Biochemistry and Molecular Biology,Chemistry, Plant Biology
Emeritus Director of the CCRC
Structures and functions of oligosaccharins, biological active complex carbohydrates in plant cell walls
keywords and Selected Recent Publications
Short Biography:Dr. Albersheim received his B.S. in plant pathology in 1956 from Cornell University and his Ph.D. in biochemistry in 1959 from the California Institute of Technology. He and Dr. Alan Darvill founded the CCRC in September 1985. Prior to coming to the University of Georgia, Dr. Albersheim spent 21 years as a professor of biochemistry in the Departments of Chemistry and Molecular, Cellular and Developmental Biology. Dr. Darvill and Dr. Albersheim co-direct the CCRC as well as their combined research teams. Dr. Albersheim is also co-director of the Department of Energy-funded Center for Plant and Microbial Complex Carbohydrates. From 1990 to 2002, he was director of the National Institutes of Health-supported Resource Center for Biomedical Complex Carbohydrates. Dr. Albersheim was the 1973 recipient of the Charles A. Shull award of the American Society of Plant Physiologists and in 1984 of the Kenneth A. Spencer award of the American Chemical Society. He is a frequently invited speaker to special symposia, meetings of scientific societies, and to civic, commercial, and academic organizations in the U.S. and around the world. Full publications: 311.
Research Interests:Our laboratory has discovered that oligosaccharides act as signal molecules in plants. Hormonal concentrations of biologically active oligosaccharides, called oligosaccharins, regulate growth and development as well as defense reactions by regulating gene expression. Most importantly, oligosaccharins have exquisitely specific structural requirements. The first oligosaccharide shown to possess biological activity was a hepta-b-glucoside isolated from the mycelial wall of a fungal pathogen of soybeans. The active hepta-b-glucoside, which at 10-9 M causes soybean cells to make phytoalexins (antibiotics), was the only active hepta-b-glucoside of about 300 different hepta-b-glucosides generated from the b-glucan by partial acid hydrolysis.
A mixture of large oligoglucoside fragments of the same mycelial wall b-glucan that contains the hepta-b-glucoside elicitor of phytoalexins has a different effect when sprayed on the leaves of tobacco plants. Only very small amounts of the oligoglucosides need to be sprayed on the leaves to protect them against viral infection. But the fragment of the b-glucan that protects tobacco against viral infection is not the same hepta-b-glucoside that elicits production of phytoalexins in soybeans. Thus, two different oligosaccharide fragments of the same polysaccharide regulate different defense mechanisms.
Oligogalacturonide fragments of cell wall homogalacturonans were the first oligosaccharin to be isolated from a plant cell wall polysaccharide. Linear a-1,4-D-oligogalacturonides containing 12 to 14 galactosyluronic acid residues have the same biological effect as the active hepta-b-glucoside: they elicit soybean seedlings to produce phytoalexins. Moreover, the hepta-b-glucoside (a neutral oligosaccharide of fungal cell wall origin) and oligogalacturonide elicitors (pure polyanionic oligosaccharides of plant cell wall origin) act synergistically when activating the expression of the genes that encode the enzymes that synthesize phytoalexins, requiring the presence of less of each to stimulate phytoalexin production when both are present.
We hypothesize that other plant cell wall oligosaccharide fragments, solubilized by pathogen-secreted enzymes, trigger the widely observed and physiologically important hypersensitive resistance response. Hypersensitive resistance is evidenced by the death, in a resistant (incompatible) plant, of the first plant cells to come in contact with an infecting microbe. The enzymes secreted by a fungal pathogen of rice plants release fragments of plant cell walls that kill plant cells, and the active fragments appear to be part of arabinoxylan, a hemicellulose present in the cell walls of all higher plants.
Oligosaccharins are also involved in regulating growth and development of plants. The plant hormone auxin doubles the rate of elongation growth of excised segments of pea stems. A particular nonasaccharide fragment of xyloglucan, at a concentration of 10-8 to 10-9 M, inhibits auxin-stimulated growth of pea stem segments. A variety of other xyloglucan fragments are not active in inhibiting auxin-stimulated growth. A cell wall enzyme, an a-fucosidase, destroys the inhibitory activity of the nonasaccharide when it removes the terminal fucosyl residue. We are cloning the a-fucosidase and a b-1,4-endoglucanase (also of cell wall origin) that modify and generate the bioactive xyloglucan oligosaccharides in order to study their in vivo role in growth.
Other oligosaccharins inhibit the formation of roots and stimulate the production of flowers. The Albersheim/Darvill and Mohnen research teams developed a tobacco explant system to study the effect of wall fragments on morphogenesis. The explants we are studying are cut from the stems of flowering tobacco plants and are about 1 cm long, 1 mm wide, and 5 to 10 cells thick. We can determine the morphogenetic fate of the explants by regulating the concentrations of just two factors, the hormones auxin and cytokinin. Relatively high auxin and low cytokinin concentrations cause the explants to form only roots; at high cytokinin and low auxin, the explants form only vegetative shoots; and at low auxin and low cytokinin, the explants form flowers. Plant cell wall fragments released by the action of an a-1,4-endopolygalacturonase inhibit the formation of roots and stimulate the formation of flowers.
The root-inhibiting and flower-stimulating oligosaccharin in the mixture of oligo- and polysaccharides released from the walls by the enzyme is linear a-1,4-D-oligogalacturonides with a degree of polymerization of 12 to 14. These are the same oligogalacturonides that elicit phytoalexins to form in soybean seedlings, but 100 times less oligogalacturonide (~10-7 M) is required to stimulate flowers to form than to stimulate phytoalexin production.
We are studying the mechanism of action of the oligogalacturonides. We now know that within two minutes of exposure to the oligogalacturonides a variety of plasma membrane functions are transiently altered, such as an efflux of potassium ions, an influx of calcium ions and protons, as well as a major depolarization of the plasma membrane. Efforts are under way to determine whether these membrane effects lead to the physiological and morphological effects of oligogalacturonides.
Dr. Albersheim's work is supported by the National Institutes of Health, the U.S. Department of Energy, and industrial sources.
Keywords and Selected Recent Publications:Keywords: Oligosaccharins, host-pathogen interaction, plant cell walls, polysaccharides, rhamnogalacturonan I, rhamnogalacturonan II, xyloglucan, oligogalacturonides, signal molecules, phytoalexins, homogalacturonan, PGIP, pectic polysaccharides, fungal enzymes
Selected Recent Publications
Williams, M.N.V., G. Freshour, A.G. Darvill, P. Albersheim, and M.G. Hahn. 1996. An antibody Fab selected from a recombinant phage display library detects deesterified pectic polysaccharide rhamnogalacturonan II in plant cells. The Plant Cell 8: 673-685.
Albersheim, P., A.G. Darvill, M.A. O'Neill, H.A. Schols, and A.G.J. Voragen. 1996. An hypothesis: The same six polysaccharides are components of the primary cell walls of all higher plants. In: Pectins and Pectinases - Proceedings of a Conference (J. Visser, ed.), pp. 47-55. Elsevier Publishers, Amsterdam.
Albersheim, P., A. Darvill, K. Roberts, L.A. Staehelin, and J.E. Varner. 1997. The structures of cell wall polysaccharides define their mode of synthesis. Plant Physiol. 113: 1-3.
Ham, K.-S., A.G. Darvill, and P. Albersheim. 1997. Fungal pathogens secrete an inhibitor protein that distinguishes isoforms of plant pathogenesis-related endo-b-1,3-glucanases. Plant J. 11: 169-179.
Wu, S.-C., K.-S. Ham, A.G. Darvill, and P. Albersheim. 1997. Deletion of two endo-b-1,4-xylanase genes reveals additional isozymes secreted by the rice blast fungus. Mol. Plant-Microbe Interact. 10: 700-708.
Hantus, S., M. Pauly, A.G. Darvill, P. Albersheim, and W.S. York. 1997. Structural characterization of novel L-galactose-containing oligosaccharide subunits of jojoba seed xyloglucans. Carbohydr. Res. 304: 11-20.
Strickland, F.M., A. Darvill, P. Albersheim, S. Eberhard, M. Pauly, and R.P. Pelley. 1999. Inhibition of UV-induced immune suppression and interleukin-10 production by plant oligosaccharides and polysaccharides. Photochem. Photobiol. 69: 141-147.
Cook, B.J., R.P. Clay, C.W. Bergmann, P. Albersheim, and A.G. Darvill. 1999. Fungal polygalacturonases exhibit different substrate degradation patterns and differ in their susceptibilities to polygalacturonase inhibiting proteins. Mol. Plant Microbe Interact. 12: 703-711.
Pauly, M., P. Albersheim, A. Darvill, and W.S. York. 1999. Molecular domains of the cellulose/xyloglucan network in the cell walls of higher plants. The Plant J. 20: 629-639.
Rose, J.K.C., D.J. Cosgrove, P. Albersheim, A.G. Darvill, and A.B. Bennett. 2000. Detection of expansin proteins and activity during tomato fruit ontogeny. Plant Physiol. 123: 1583-1592.
Vidal, S., T. Doco, P. Williams, P. Pellerin, W.S. York, M.A. O'Neill, J. Glushka, A.G. Darvill, and P. Albersheim. 2000. Structural characterization of the pectic polysaccharide rhamnogalacturonan II: Evidence for the backbone location of the aceric acid-containing oligoglycosyl side chain. Carbohydr. Res. 326: 277-294.
Pauly, M., Q. Qin, H. Greene, P. Albersheim, A. Darvill, and W.S. York. 2001. Changes in the structure of xyloglucan during cell elongation. Planta 212: 842-850.
Pauly, M., S. Eberhard, P. Albersheim, A. Darvill, and W.S. York. 2001. Effects of the mur1 mutation on xyloglucans produced by suspension-cultured Arabidopsis thaliana cells. Planta 214: 67-74.
Rose, J.K.C., K.-S. Ham, A.G. Darvill, and P. Albersheim. 2002. Molecular cloning and characterization of glucanase inhibitor proteins: Coevolution of a counterdefense mechanism by plant pathogens. Plant Cell 14: 1329-1345.
Qin, Q., C.W. Bergmann, J.K.C. Rose, M. Saladie, V.S. Kumar Kolli, P. Albersheim, A.G. Darvill, and W.S. York. 2003. Characterization of a tomato protein that inhibits a xyloglucan-specific endoglucanase. Plant J. 34: 327-338.
Bergmann, C.W., L. Stanton, D. King, R.P. Clay, G. Kemp, R. Orlando, A. Darvill, and P. Albersheim. 2003. Recent observations on the specificity and structural conformation of the polygalacturonase-polygalacturonase inhibiting protein system. In: Advances in Pectin and Pectinase Research (F. Voragen, H. Schols, and R. Visser, eds.), pp. 277-291. Kluwer Academic Publishers, The Netherlands.
Kolli, V.S.K., J. Johnson, R. Orlando, A.G. Darvill, P. Albersheim, and S.-C. Wu. 2003. Proteomic identification of extracellular proteins secreted by the rice blast fungus. In: Proceedings of the 51st American Society of Mass Spectrometry Conference, Montreal, Canada, June 8-12.
Kemp, G., L. Stanton, C.W. Bergmann, R.P. Clay, A. Darvill, and P. Albersheim. 2004. Polygalacturonase-inhibiting proteins can function as activators of polygalacturonase. Mol. Plant-Microbe Interac. 17: 888-894.
Wu, S.-C., J. Johnson, A.G. Darvill, P. Albersheim, and R. Orlando. 2004. Proteomics of Magnaporthe grisea: liquid chromatography mass spectrometry for the identification of extracellular proteins. In: Rice Blast: Interaction with Rice and Control (S. Kawasaki, ed.), pp. 39-46. Kluwer Press, Dordrecht, The Netherlands.
Wu, S.-C., J. Halley, A.G. Darvill, and P. Albersheim. 2006. Identification of a endo-b-1,4-D-xylanase from Magnaporthe grisea by gene knockout analysis, purification , and heterologous expression. Applied Environ. Microbiol. 72: 986-993.