observed that plant diseases can be suppressed by treatments that modify the microbial community of the root to make it more like the community in the soil, a conclusion which they have dubbed the “camouflage hypothesis.” By analogy, the human intestinal microflora may influence the success of pathogens by either presenting a barrier to invasion that is predicated on the composition of the entire community, or conversely by potentiating activity, facilitating infection, or aggravating disease symptoms.

The second contribution to this chapter, by plant biologist Brian Staskewicz, describes similarities among the strategies used by plant and animal pathogens and compares the defenses mounted against them by their disparate hosts. The complexity of disease resistance in plants is illustrated through Staskewicz’s description of his laboratory’s efforts to describe the function and regulation of a key disease resistance protein in the plant Arabidopsis thaliana, in response to the pathogenic bacterium, Pseudomonas syringae.

Conserved cellular defense responses in plants resemble certain innate immune responses to pathogens in vertebrates and insects, suggesting that these defense pathways may be inherited from a common ancestor. The preponderance of conserved motifs and, presumably, mechanisms among plant and animal proteins involved with innate immunity has encouraged communication and even collaboration among the scientists who study these systems in widely different species—an unfortunately rare occurrence that may yield significant insights on the structure, function, and evolution of innate immunity.


Christina Matta and Jo Handelsman1


The microbial communities that reside on and inside plants and animals are a key to host health. In addition to contributing to digestion and nutrition, they present a formidable barrier to pathogens, which may invade the community or arise from it. The future of infectious disease research needs to focus on ways to enlist the natural community in prevention of disease rather than solely on the traditional warfare model, which requires direct killing of the pathogen with a chemical agent. The future of this field will depend on insights into the nature of cooperation within communities and the features that make them resistant to invasion. In these areas, the field of plant pathology, or infectious disease of plants, has much to offer. Plant pathologists have long recognized the role of the micro-


C. Matta is from the Department of History of Science and J. Handelsman is from the Department of Plant Pathology, both of the University of Wisconsin, Madison, WI.

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