Our goal is to understand the molecular mechanisms that enable bacteria to attack plants. Much of our current work is focused on Pseudomonas syringae pv. tomato DC3000, which is a pathogen of tomato and the model plant Arabidopsis thaliana. Like many host-specific plant pathogens, P. syringae is a "stealth" parasite that can multiply for several days in host tissues before symptoms, such as necrotic spots, develop. We have learned that the ability of P. syringae to multiply in the intercellular spaces of plant leaves and cause disease is dependent on a "type III" secretion system that injects virulence effector proteins into host cells. Variants of this injector system are also used by many important animal pathogens (for example, Yersinia pestis, the plague pathogen) to deliver their virulence proteins. What is the complete repertoire of effectors and injectisome components secreted by P. syringae? How do effectors subvert host defenses? What other adaptations does this sophisticated parasite have for life in plants? To answer these questions, we and a team of researchers from the USDA/ARS Plant-Microbe Interaction research group at Cornell and the Boyce Thompson Institute for Plant Research have been characterizing the genome sequence of DC3000 and developing a variety of bioinformatic, biochemical, genetic, and cell biological tools to support a genome-wide study of virulence mechanisms and to foster functional genomic investigations by the worldwide research community.