Gregory B. Martin was born in 1956 in Lansing, MI. He received his B.S. (1979), M.S. (1984), and Ph.D. (1989) degrees from Michigan State University (MSU). His Ph.D. work was pursued in the Genetics Program at the MSU-Department of Energy Plant Research Lab. From 1982 to 1983, he was a visiting scientist with the U.S. Agency for International Development at the University of Malawi, Lilongwe, Malawi. From 1989 to 1992, he was an National Science Foundation Post-Doctoral Fellow in the Department of Plant Breeding at Cornell University, and from 1992 to 1998, he was an assistant professor and then associate professor in the Department of Agronomy at Purdue University. In 1998, he returned to Ithaca and the Boyce Thompson Institute for Plant Research where he now holds a joint appointment as the Boyce Schulze Downey chair and a professor in the Department of Plant Pathology and Plant-Microbe Biology at Cornell University.
Martin’s research focuses on the mechanisms that bacteria use to infect plants and, in turn, the mechanisms that plants have evolved to interfere with bacterial pathogens. The interaction of tomato with Pseudomonas syringae pv. tomato has been the model system for this work. His career is marked by a series of major discoveries that have been published in the top tier of science journals: Cell, Nature, Science, Proceedings of the National Academy of Sciences USA, and EMBO Journal. The first of these landmark papers was the 1993 report in Science of the cloning of the tomato Pto gene, the first recognitional resistance gene to be cloned. This achievement, based on innovative positional cloning techniques, was made when Martin was a post-doctoral fellow with Steven Tanksley at Cornell. The cloning of Pto followed by nine years the cloning of the first pathogen avirulence gene by Brian Staskawicz and Noel Keen; thus, it inaugurated a new era in the study of pathosystems involving gene-for-gene interactions in which the determinative host and pathogen proteins could be studied directly with the tools of biochemistry and structural biology.
Martin’s research program has maintained Pto as its centerpiece and has been remarkably productive in revealing a world of complex molecular interactions and new paradigms for molecular plant pathology. A surprising discovery attending the initial identification of Pto was that it encoded a cytoplasmic protein kinase. At Purdue, Martin and his post-doctoral associates Jian-min Zhou and Xiaoyan Tang pursued that clue and used yeast two-hybrid techniques to demonstrate that Pto physically interacts with AvrPto, the cognate avirulence (type III effector) protein produced by P. syringae pv. tomato. By constructing mutations in Pto and avrPto and observing that loss of physical interaction between the proteins resulted in loss of defense activation, they provided the first molecular explanation for gene-for-gene specificity.
Genetic evidence had suggested that P. syringae pv. tomato produces a second type III effector protein that is recognized by Pto. The Martin lab discovered this protein, AvrPtoB, by using a yeast two-hybrid screen for P. syringae pv. tomato proteins that could interact with Pto. The study of AvrPtoB by Martin and two graduate students, Robert Abramovitch and Tracy Rosebrock, demonstrated that evolution of gene-for-gene interactions can occur at the level of domains within a single protein. The C-terminal domain of AvrPtoB was found to suppress recognition of an N-terminal domain. Determination of the structure of the C-terminal domain, in collaboration with C. Erec Stebbins at Rockefeller University, revealed an unexpected homology with eukaryotic E3 ubiquitin ligases. The N-terminal domain of AvrPtoB was then found to interact with Fen (a member of the Pto kinase family). This interaction triggers plant defense unless the E3 ubiquitin ligase activity of the C-terminal portion of AvrPtoB is present. The latter specifically ubiquitinates Fen and targets it for proteasome degradation. Pto is not ubiquitinated by AvrPtoB, which suggests an evolutionary scenario in which Fen is an ancient R protein that was defeated when AvrPtoB acquired its E3 ligase domain and was subsequently supplanted by a new R protein (Pto).
Recent studies by Jijie Chai and Jian-min Zhou at the National Institute of Biological Sciences in Beijing and Jen Sheen at Harvard Medical School in collaboration with Martin, have revealed that AvrPto and AvrPtoB are inhibitors of pattern recognition receptor complexes that detect flagellin and other pathogen-associated molecular patterns. These observations, along with important structural biology insights from Jijie Chai have supported the concept that Pto may act as a “decoy” kinase, whose perturbation by these effectors is the seminal event in triggering resistance. Martin and his many collaborators have provided key components in a new conceptual framework for plant-bacterium interactions that involves type III effectors interacting with two levels of plant defense, and their studies have revealed a remarkable degree of molecular subterfuge by both host and pathogen in the evolution of gene-for-gene interaction systems.
The elegance and rigor of this work and many other studies by the Martin group has helped to connect molecular plant pathology with the broader research community that is studying innate immunity and signal transduction in higher eukaryotes. Martin has disseminated this knowledge through lucid review articles and through invited talks at meetings of the International Society for Molecular Plant-Microbe Interactions, The American Phytopathological Society, and numerous other scientific gatherings and seminars. As examples of the latter, he has been a Grand Marnier Foundation lecturer at the Pasteur Institute and a post-doc/student invited lecturer in the Department of Molecular Biology at Harvard Medical School. Martin also has been a key participant in consortia developing genomics resources for tomato and, with Alan Collmer at Cornell, P. syringae pv. tomato. He has served as director of the Center for Gene Expression Profiling at the Boyce Thompson Institute and as a member of the Editorial Board of The Plant Journal, from 1999 to 2004. Martin was elected in 2004 as a fellow of the American Association for the Advancement of Science and in 2005 as a fellow of the American Academy of Microbiology.
