My group studies the pathogenic lifestyle of Xanthomonas campestris pathovar vesicatoria (Xcv), the causal agent of bacterial spot disease of tomato and pepper.  Our research is aimed at elucidating the biochemical role of type III effector proteins in plant pathogenesis.  Many plant (and animal) bacterial pathogens use a conserved type III secretion system (TTSS) to inject proteins into their eukaryotic hosts.  Interestingly, Xcv mutants lacking a functional TTSS cannot multiply within plant tissue.  The TTSS apparatus and its effector substrates function together to suppress the plant’s basal- and resistance protein-mediated innate immune responses.  Thus, the TTSS and its effectors are essential virulence determinants required for bacterial colonization and persistence in plants.  Currently, the biochemical basis for TTSS effector function inside plant cells during infection is still a mystery. To gain insight into the tricks used by bacteria to manipulate host signaling, we use modern biochemical, cell biological, and genetic approaches using the natural host tomato.  When appropriate, we also use two model pathosystems, Xanthomonas-Arabidopsis and Xanthomonas-Nicotiana benthamiana, to exploit the available genomic resources and biochemical techniques, respectively.