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Gregory B. Martin
The recipient of the Herbert Newby McCoy Award for 1997 is Gregory B. Martin, Associate Professor of Agronomy. Professor Martin was born in East Lansing, Michigan, where he later attended Michigan State University, obtaining a B.S. in crop science and a Ph.D. in genetics at the MSU/DOE " Plant Research Laboratory. Martin held an NSF plant biology fellowship to conduct postdoctoral research at Cornell University. He joined the Purdue agronomy department in 1992, where he teaches Introduction to Genetics, AGRY 320. Martin was awarded a David and Lucile Packard fellowship in 1995. In addition to the Packard fellowship, Professor Martin's research is supported by the NSF, USDA, USDA-BARD, and Monsanto. His research on plant disease resistance is described in over 25 publications and he has presented more than 50 lectures at universities and various national and international meetings over the past five years.
Diseases caused by bacteria, fungi, viruses, and nematodes cause major economic losses to crops throughout the world. Research in Professor Martin's laboratory focuses on understanding the molecular basis of pathogen recognition and subsequent signal transduction events that are involved in plant disease resistance. The work focuses on resistance to bacterial speck disease in tomato that is governed by a "gene-for-gene" interaction in which the Pto resistance gene in the plant recognizes the expression of the avrPto avirulence gene in the pathogen. Pto encodes a protein kinase and avrPto encodes a small hydrophilic protein. Martin's research team investigated the role of Pto and AvrPto in plant-pathogen recognition and found that the two proteins physically interact in the plant cell. The team currently is determining the recognition specificity domains of both AvrPto and Pto and is testing specific models to understand how the physical interaction of these two proteins initiates disease resistance. To understand the role of the Pto kinase in signal transduction, researchers in Professor Martin's laboratory isolated genes from tomato that encode Pto-interacting (Pti) proteins. Pti proteins include a protein kinase (Pti1) and a class of DNA-binding proteins (Pti4/5/6). Martin will discuss these data and present a model for the molecular basis of Pto- mediated disease resistance.
Professor Martin's work focuses on understanding the molecular basis of disease resistance in plants, Most of his work has been with tomato bacterial speck disease, which is caused by the organism Pseudomoeas syringae pv. tomato. Resistance to bacterial speck is typical of many "gene-for-gene" interactions, in which a single resistance (R) gene in the plant responds to the expression of a single "avirulence" (avr) gene in the pathogen. In the case of bacterial speck disease, the Pto resistance gene in tomato responds to the expression of the avrPto gene in the bacterium. Disease susceptibility results if either Pto or avrPto is absent in the corresponding organisms. Martin applied a new gene isolation strategy termed "map-based" cloning to isolate the Pto resistance gene. Pto was the first gene to be isolated from a crop plant species using map-based cloning and was the first plant disease resistance gene that participates in a gene-for-gene interaction to be molecularly characterized. Pto proved to encode a serine-threonine protein kinase that has roles in both recognition of the pathogen and in signal transduction leading to the activation of plant defense responses. Since the early 1980s, it had been proposed that the molecular basis of gene-for-gene interactions might be the physical interaction of a signal molecule produced by the pathogen and a receptor produced by the plant R gene. However, it had been unclear how such an interaction could occur in bacterial speck resistance since Pto is probably a cytoplasmic protein and there was no evidence that the AvrPto protein is secreted from the bacterial cell. Martin's team recently showed that the bacterial AvrPto protein functions directly in plant cells and physically interacts with the Pto kinase. These observations provided the first explanation of the molecular basis of a recognition process that occurs between plants and their bacterial pathogens. To understand the steps in the Pto signaling pathway, Martin's laboratory used the yeast two-hybrid system to identify several Pto-interacting (Pti) proteins. One of these, Ptil, encodes a protein kinase that appears to lie downstream of Pto in a pathway leading to the localized cell death termed the "hypersensitive response." Another series of proteins, Pti4, Pti5, and Pti6, encode putative transcription factors that are implicated in the activation of a large family of "pathogenesis-related" (PR) genes. Professor Martin's research over the past five years at Purdue permitted the development of a comprehensive model to explain the molecular basis of bacterial speck disease resistance. In this model, it is proposed that the AvrPto protein is secreted by Pseudomonas directly into plant cells where it physically interacts with the cytoplasmic kinase Pto. The physical interaction of Pto and AvrPto determines the specific recognition between plants with the Pto gene and Pseudomonas bacteria carrying avrPto. This recognition event, which also may involve the Prf protein (known to be required for Pto-mediated resistance), activates the Pto kinase. In response, the Pto kinase phosphorylates and activates diverse downstream target proteins, each of which plays a unique role in signaling the resistance response. Ultimately, disease resistance is determined by the activation of a variety of defense responses including the oxidative burst, defense gene expression, and the hypersensitive response. In the course of his research at Purdue, Gregory Martin has worked with Professors Ray Bressan, Alan Friedman, Phil Low, Sally MacKenzie, Randy Woodson, and many outstanding graduate students and postdoctoral scientists.