SFB796 - Sub project C5
(sub project concluded on Mar 31 2013)


Functional characterisation of bacterial type III effectors targeting host cell vesicle trafficking


Project summary

Pathogenicity of many Gram-negative pathogenic bacteria depends on a type III secretion system, which translocates bacterial effector proteins into the host cell. These type III effector proteins (T3Es) have evolved to function in a eukaryotic context in order to promote colonization of the host. The molecular mechanisms by which these T3Es alter host cellular processes are far from being understood. In the first funding period we were able to show that XopJ, a T3E of the plant pathogenic bacterium Xanthomonas campestris pv. vesicatoria is able to suppress host cell vesicle trafficking and thus cell-wall based basal defense. Using a variety of methods it could be demonstrated that XopJ interacts with RPT6, a subunit of the host proteasome, and thereby inhibits proteasome activity. This effect is dependent on an intact catalytic triad sequence of XopJ as well as on plasma membrane targeting of the effector. In further experiments we will clarify the biochemical mechanism by which XopJ inhibits RPT6 function and also seek to establish a link between proteasome activity and defense responses. In addition, we were able to show that HopZ1a, a T3E from Pseudomonas syringae belonging to the same effector family as XopJ, is an acetyltransferase able to inhibit secretion although likely through a different mechanism which involves disturbance of the cytoskeleton. Using yeast two-hybrid screenings we have identified a remorin protein as a potential target protein of HopZ1a in tobacco. Future experiments will investigate the relationship between HopZ1a/remorin interaction and the suppression of plant defence.

Colocalisation of XopJ::GFP and a plasma membrane transporter mCherry fusion. The plasma membrane transporter localizes around the nucleus and in the plasma membrane whereas XopJ::GFP is attached to the plasma membrane via putative myristoylation and palmitoylation sites. Chloroplasts are shown in blue.

XopJ represses callose deposition after infection. Ethanol-inducible XopJ-expressing Arabidopsis thaliana plants were infected with Pseudomonas syringae pv. tomato DC3000 (Pst), which was deficient in the T3SS. XopJ reduces callose depositions after infection of the plants with an avirulent Pst strain.


Project related publications

  • Üstün, S., Müller, P., Palmisano, P., Hensel, M., Börnke, F.   (2012).   SseF, a type III effector protein from the mammalian pathogen Salmonella enterica, requires resistance-gene mediated signalling to activate cell death in the model plant Nicotiana benthamiana.   New Phytologist 194: 1046 - 1060.

  • Lee, A.H., Hurley, B., Felsensteiner, C., Yea, C., Ckurshumova, W., Bartetzko, V., Wang, P.W., Van, Q., Lewis, J.D., Liu, Y.L., Börnke, F., Angers, S., Wilde, A., Guttman, D.S., Desveaux, D.   (2012).   A bacterial acetyltransferase destroys plant microtubule networks and blocks secretion.   PLoS Pathogens 8(2):e1002523.

  • Hoefle, C., Huesmann, C., Schultheiss, H., Börnke, F., Hensel, G., Kumlehn, J., Hueckelhoven, R.   (2011).   A barley ROPGTPase ACTIVATING PROTEIN associates with microtubules and regulates entry of the barley powdery mildew fungus into leaf epidermal cells.   Plant Cell 23: 2422 - 2439.

  • Bartetzko, V., Sonnewald, S., Vogel, F., Hartner, K., Stadler, R., Hammes, U. Z. and Börnke, F.   (2009).   The Xanthomonas vesicatoria pv. campestris type III effector protein XopJ inhibits protein secretion: evidence for interference with cell wall – associated defense responses.   Mol Plant-Microbe Interact 22, 655-664.