Analysis of membrane-associated components of the type III secretion system from Xanthomonas campestris pv. vesicatoria

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The plant pathogenic bacterium Xanthomonas campestris pv. vesicatoria employs a type III secretion (T3S) system to translocate effector proteins directly into the host cell cytosol. The membrane-spanning secretion apparatus consists of eleven conserved and several non-conserved components. In this project, we will perform in vitro and in vivo protein-protein interaction studies with predicted inner and outer membrane components of the T3S system to gain first insights into the assembly of this molecular nanomachine. Furthermore, we will test possible interactions between inner membrane-associated components and secreted proteins to identify substrate docking sites of the T3S system. The biological significance of our findings will be addressed by genetic approaches. We also aim at the identification of functional residues in the cytoplasmic region of the inner membrane protein HrcU, which is involved in the control of T3S substrate specificity. HrcU belongs to the FlhB/YscU protein family that was studied in animal pathogenic bacteria. Notably, our recent experiments revealed striking differences to the mechanisms proposed for the FlhB/YscU-mediated substrate specificity switch in animal pathogens. It is therefore likely that control mechanisms of T3S systems vary significantly among different pathogens.