1999 McCoy Award Recipient
Ray A. Bressan
Professor Horticulture and Landscape Architecture

Professor Ray A. Bressan, professor of horticulture, was presented the prestigious award during this year's ceremony held April 16, 1999, for his significant discoveries and contributions in the field of plant biology.

Dr. Bressan is a faculty member in Purdue's Department of Horticulture and Landscape Architecture. His outstanding research program in plant biology has led to the following important discoveries and noteworthy contributions:

• The identification and characterization of a new class of genes, the osmotins, which are involved in plant tolerance to environmental and biological stresses.
• The transformation of potato with an anti-fungal gene and the demonstration of resulting enhanced disease resistance in this major crop as well as its potential use in other crops.
• The development of the first successful genetic transformation system for sorghum, opening the potential for modification of this important world crop through genetic engineering technology.
• The discovery of a novel mechanism of protein-induced cell death in fungi and the resulting application of this to the broad area of genetic engineering for disease resistance in crop species.

Prof. Bressan has received over $10 million in extramural funding for support of his research. He is recognized internationally for his research program in the area of plant stress physiology. He has joined numerous collaborators at Purdue and other universities across the world to establish a research program focusing on this important area of plant science.

Prof. Bressan has published over 110 papers and presented over 100 invited lectures. He has trained 14 Ph.D. students, supervised 34 postdoctoral fellows, and has hosted 32 visiting scientists. He has taught and guest lectured to numerous regular classes, and specialized graduate level classes in the areas of plant stress physiology, somatic cell genetics, and plant gene expression.

Prof. Bressan belongs to a number of societies. His primary interest, however, is with the American Society for Plant Physiologists. He serves on the editorial boards of Plant Physiology and In Vitro, Plant Section. He has held appointments on the USDA competitive grants panel for environmental stress. He frequently reviews manuscripts for Plant Molecular Biology, PNAS, Plant Cell Reports, Plant Cell and Environment, Physiologia Plantarum, Plant Cell, Plant Journal, Crop Science, Science, Plant Physiology, and the Journal ASHS. Every year he also reviews several competitive grant proposals submitted to NSF, DOE, and USDA panels.

Prof. Bressan's research program extends into many departmental laboratories here at Purdue and other universities across the nation and the world. He brings people together in productive collaborative efforts. He significantly contributes to the professional development and vision of the collaborative mode of research.

Abstract of talk
Plants produce a plethora of toxic proteins, and many have been shown to act in defense against predatory or pathogenic organisms that they encounter . Although the induction of defense protein accumulation by plants has been extensively studied, the mechanisms by which these toxins act to protect against invasive organisms is poorly understood. The common bakers yeast Saccharomyces cerevisiae has been used extensively as a molecular and genetic model organism. It has also proven invaluable in our studies on the mechanism of action of plant defensive proteins. Using yeast as a model we have demonstrated that the plant antifungal protein osmotin is dependent on the function of several genes which control important properties of the fungal cell wall including the pir genes and genes encoding components of an osmotin-induced signal pathway. Osmotin toxicity is also dependent on mnn4, mnn6 and mnn2, genes which are required for the transfer of mannosylphosphate to cell wall mannans. The mnn2 gene encodes an a -1,2-mannosyltransferase catalyzing the addition of the first mannose to the branches on the poly-l,6-mannose backbone of the outer chain of cell wall N-linked mannans. Null mnn4, mnn6 or mnn2 mutants are defective in alcian blue binding and osmotin binding. Antimannoprotein antibodies or alcian blue protect cells against osmotin cytotoxicity. The mnn1 gene encodes an a -1,3-mannosyltransferase that adds the terminal mannose to the outer chain branches of N-linked mannan. Null mnn1 mutants exhibit enhanced alcian blue binding, osmotin binding and osmotin sensitivity. Several cell wall mannoproteins bind immobilized osmotin or alcian blue. Thus mannosylphosphate residues on yeast cell wall mannans are inferred to function as osmotin receptors that facilitate its cytotoxicity. In addition, overexpression of the Oss1 gene caused super-sensitivity to osmotin. This gene encodes a seven transmembrane receptor-like protein. The OSS1 protein specifically binds to active but not to inactive isoforms of osmotin, and may thus represent the plasmamembrane receptor for these toxins. Intoxication by osmotin leads to a series of progressive cytological changes in target cells that indicates it is an inducer of program cell death. This induction occurs via a signal pathway independent of the main mitochondrial mediated pathway known in yeast.

Research
Dr. Bressan joined the Purdue faculty in 1978 and immediately set out to establish a vital research program in the area of osmotic stress responses in plants. Using plant cell cultures, Dr. Bressan established that osmotic adaptation was a cellular developmental process generally inherent in virtually all plant species and not a special characteristic of halophytes or xerophytes as previously thought. His work in this area laid the foundation for establishing the importance of several metabolic processes that could (and would) eventually be manipulated by genetic engineering to affect osmotic tolerance. His group was among the first to identify proteins that accumulate in cells in response to osmotic stress or following adaptation to osmotic stress. They designated one class of these proteins as osmotins, and have gone on in recent years to establish the intricate relationship of the osmotins to both abiotic and biotic stress. Ray's group carefully characterized the regulation of the osmotin gene providing the first evidence for the synergistic activity of two plant hormones in regulating gene transcription (Xu et al. 1994, Plant Cell). To date, osmotin remains one of the most well characterized stress-induced genes with detailed information on the cis-elements and trans-acting factors involved in it's transcriptional regulation.

Work in Ray's lab took a major turn in recent years with the discovery that osmotin could protect plants from fungal pathogens (Liu et al. 1994, PNAS). In this pioneering paper, they described the development of disease resistance in potato plants overexpressing the osmotin gene. This result has led a number of other investigators to exploit the anti-fungal activity of osmotin in developing disease resistant crop plants. Since the initial demonstration by Woloshuk et al. (1991, Plant Cell), that osmotin could inhibit fungi in vitro, Dr. Bressan has pioneered a very active field of investigation into the mechanism of action of antifungal proteins. Ray's group knew that osmotin, and other anti-fungal proteins, exhibited clear specificity, indicating that there must be cellular determinants of sensitivity and resistance in fungal cells. This led Dr. Bressan to exploit the genetics of yeast in an effort to identify targets on the cell wall or plasma membrane that interact with osmotin. Initially, they identified genetic variants of yeast with increased sensitivity to osmotin. Subsequently, Dr. Bressan's group identified a member of a gene family from yeast encoding a stress protein localized to the cell wall. When this gene was overexpressed in yeast, the transgenic cells exhibited increased resistance to osmotin (Yun et al. 1997, PNAS). This result clearly showed that proteins localized to the cell wall are determinants of resistance to osmotin. Current evidence from Bressan's laboratory indicates that osmotin interacts with cell wall proteins and a membrane receptor to initiate a signaling cascade culminating in fungal cell death. This work was published in the prestigious journal Molecular Cell.

Dr. Bressan has been extremely active in collaborating with several colleagues at Purdue on his research. His work on osmotic and other stress at Purdue involves collaborations with Professors Hasegawa, Handa, Rhodes, Carpita, Csonka, Gelvin and Murdock. Dr. Bressan has a long standing collaboration with Mike Hasegawa that serves as an excellent example of "team" science. Together, they have explored issues related to osmotic stress and tolerance for over 20 years. Recently, these scientists established that activation of a stress signaling cascade in plants can result in adaptations that mediate salt tolerance (Pardo et al., 1998). Research with Csonka resulted in the identification of the first polycistronic locus in tomato (Garcia-Rios et al., 1997) and with Murdock the determination that carbohydrate binding mediates the insectidal activity of the plant defense lectin GSII (Zhu-Salzman et al., 1998). As part of a McKnight Foundation funded project, Dr. Bressan collaborated with professors Hasegawa, Butler and Axtell to develop the first successful genetic transformation system for sorghum (Casas et al. 1993, PNAS). This development is not only of great importance to commercial seed companies in the U.S., but holds immeasurable promise for the genetic improvement of sorghum for many third-world countries that depend heavily on sorghum for a staple food source. Dr. Bressan is now focusing on the introduction of several important genes into sorghum including the osmotin gene. In recent years, Ray has been an active collaborator of Dr. Greg Martin in an effort to understand the role of Pto in disease resistance in tomato (Zhou et al. 1995, Cell).

In 1998, Dr. Bressan, together with his colleague, Professor Hasegawa, joined with scientists from the University of Arizona and Oklahoma State University to prepare a plant stress genomics proposal that was funded by Plant Genome division of the National Science Foundation for $8.5 million. Research on this project will focus on the identification of all of the plant genes involved in salt tolerance.