| The Gram negative plant pathogenic bacterium, Pseudomonas syringae pv. tomato strain DC3000 (Pst DC3000) has emerged as a model for the study of plant-microbe interactions because it infects the model plant Arabidopsis thaliana. My thesis work has focused on how Pst DC3000 causes disease.; One virulence system essential for Pst DC3000 pathogenesis is the type III protein secretion system. My research provides new information on type III effector proteins in Pst DC3000, Pst DC3000 mutants with reduced virulence on A. thaliana, and the effect of transgenic expression of a Pst DC3000 type III effector, AvrE, on A. thaliana.; In collaboration with other members of the lab, I analyzed the Pst DC3000 genome for the presence of a cis promoter element, the hrp box, which is found in all known Pst DC3000 type III effector genes. The expression of these hrp box-containing genes was then assessed with both microarray and northern blot analyses. hrp box-containing genes which showed expression only in minimal medium were further characterized with an in planta translocation assay. This study revealed six orthologues of effectors known in other P. syringae pathovars and eight novel candidate effectors, one of which was shown to be secreted via the type III protein secretion system. This work has contributed to the knowledge of the effector inventory in Pst DC3000.; I also analyzed Pst DC3000 mutants which showed reduced growth in A. thaliana. Reduced virulence mutants with insertions in the PtsP, UvrD, and OprF genes were isolated. The PtsP gene encodes a phosphoenolpyruvate protein phosphotransferase, which is involved in sugar uptake and catabolite repression. UvrD encodes a DNA helicase II involved in DNA replication and repair. The OprF gene encodes an outer membrane protein F precursor.; AvrE is a type III effector in Pst DC3000. In order to study the affect of AvrE on the host plant, I expressed the avrE gene in A. thaliana under the control of a DEX-inducible promoter. After induction with DEX, avrE transgenic plants developed symptoms which mimicked Pst DC3000 infection and stomatal aperture was affected. In addition, expression of the avrE transgene promotes the growth of the non-pathogenic hrpH mutant, which cannot deliver any type III effectors. These data suggest that AvrE may promote Pst DC3000 pathogenesis in A. thaliana. (Abstract shortened by UMI.)... |
