Plant Biology

Edited by: Thomas W. Durso S. Whitham, S.P. Dinesh-Kumar, D. Choi, R. Hehl, C. Corr, B. Baker, "The product of the tobacco mosaic virus resistance gene n: similarity to toll and the interleukin-1 receptor," Cell, 78:1101-15, 1994. (Cited in more than 75 publications through August 1996) Comments by Barbara Baker, Plant Gene Expression Center, University of California, Berkeley, and United States Department of Agriculture-Agriculture Research Service, Albany, Calif. Tobacco is seldom viewed as making positive contributions to humankind, but the research reported in this paper-dealing with one of the plant's disease-resistance genes-could lead to a wide variety of healthier crops that are better able to fight invading pathogens. Researchers at the University of California, Berkeley, and at the United States Department of Agriculture's Plant Gene Expression Center (PGEC) in Albany, Calif., say they isolated tobacco's resistance gene n, which quickly triggers defense mechanisms when it recognizes pathogens. This is known as the hypersensitive response (HR). Photo: Lensart Studio HEALTHY CROP: A disease-resistance gene in tobacco resembles such genes in other plants, notes Barbara Baker. According to Barbara Baker, a senior scientist at PGEC and an adjunct professor of plant biology at UC-Berkeley, the work marks one of the first isolations of a microbial disease- resistance gene from a plant, and the first isolation of a virus-resistance gene. About the same time that Baker's team isolated gene n, other scientists at UC-Berkeley and at Harvard University were reporting the isolation of a second disease-resistance gene from the Arabidopsis plant. "Remarkably, the Arabidopsis gene looked very similar to the gene we found in tobacco," Baker declares. "The Arabidopsis gene codes resistance to a bacteria." Within weeks, other researchers had isolated disease-resistance genes from tomatoes and flax. All of these genes, states Baker, "encode a set of proteins, none of which we'd seen before in plants. The genes encode protein motifs that are similar to those of proteins that function as receptors or critical components or signal-transduction pathways in a wide variety of other organisms. "We independently showed that the genes we isolated were members of large, multi-gene families." According to Baker, the genes' remarkable similarity and their membership in multi-gene families suggest that "plants harbor many resistance genes that function for plant protection. These resistance genes compose an important part of a plant's natural protection system." Geneticists originally described resistance genes, Baker explains, "but our isolation of the genes was the first time researchers had a handle on the molecular biology of these natural plant-protection systems." Determining how the systems work offers the promise of developing "novel methods for plant protection," she continues. Researchers now can "think about moving these genes into a variety of related plants that perhaps suffer from related diseases or the same disease, when we've been unable to achieve that gene transfer through natural breeding." Baker adds: "We can now uncover, perhaps, with these first sequences, practically all resistance genes. We have molecular access to a great number of resistance genes, at least those that fall into these families; I think many do. We've isolated 10 or so, and they're all falling into these few classes of genes, and they all look very similar. That's kind of remarkable." Baker asserts that the potential applications of the findings are significant: "If we can protect crops from disease using genetic methods instead of application of pesticides and chemicals, we may be able to offer . . . safer mechanisms for crop protection." The paper's practical significance is the reason behind its high citation rate, she believes. In addition, it was one of the three original papers (the others are A.F. Bent et al., Science, 265:1856-60, 1994, and M. Mindrinos et al., Cell, 78:1089-99, 1994) that described the isolation and molecular nature of plant disease-resistance genes. "These genes had been sought after for many years," Baker notes. "The discovery that genes from very different plants encoding resistance to pathogens with such different lifestyles appear to be so similar is scientifically novel and significant."

Plant Biology

The Scientist Staff

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