project was funded by the National Science Foundation Plant Genome Research Program. C. Robin Buell, a biologist with TIGR, directed the complete sequencing of the genome. Many bacteria that are animal and plant pathogens -- including the plague bacterium Yesinia pestis -- inject virulence proteins into healthy host cells using what is called a "type III secretion system." The researchers discovered the genes encoding more than 35 injected-virulence proteins, more than for any other known pathogen, through collaboration with Cornell Theory Center computational biologists Samuel Cartinhour and David Schneider of the U.S. Department of Agriculture's (USDA) Agricultural Research Service.

P. syringae is a major agricultural pathogen, causing bacterial speck on tomatoes. It produces black lesions, often with a discrete yellow halo that can appear on the plant leaves and cause them to curl. In 1977-78 the bacteria caused serious losses to the winter tomato crop in southern Florida. Cool, moist environmental conditions contributed to the development of the disease, and it had established itself as a major problem, according to Thomas A. Zitter, Cornell professor of plant pathology.

In the years before 1977, growers had sprayed a copper-based pesticide to ward off bacterial speck, but the pathogen became resistant to the copper, rendering the pesticide virtually useless.

Natural resistance genes have been bred into certain tomato plants to control the disease. Gregory Martin, Cornell professor of plant pathology and a scientist at the Boyce Thompson Institute for Plant Research (an independent research facility on Cornell's campus), and Steven Tanksley, Cornell professor of plant breeding, cloned the first such resistance gene in 1993. The gene, Pto, enables tomato plants to recognize P. syringae and turn on strong defenses.

Over time, however, variants of the pathogen have arisen that can evade detection. Using information
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Contact: Blaine P. Friedlander Jr.
bpf2@cornell.edu
607-255-3290
Cornell University News Service
15-Aug-2003

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