SFB796 - Sub project B4
(sub project concluded on Dec 31 2012)


Reprogramming of plant metabolism by the type III effector XopB from Xanthomonas campestris pv. vesicatoria


Project summary

Xanthomonas campestris pv. vesicatoria (Xcv) is a Gram-negative bacterium that causes bacterial spot disease in tomato (Solanum lycopersicum) and pepper (Capsicum annuum) plants. The pathogenicity of Xcv depends on a type III secretion system (TTSS) delivering effector proteins into plant cells to suppress plant defence and most likely to facilitate bacterial nutrient acquisition. Since not much is known about the role of effectors in modulating plant metabolism we used the cell wall invertase (cw-Inv) as a molecular marker for metabolic changes and performed a screening of Xcv mutants to identify type three effector proteins (T3Es) which are involved in its regulation. XopB was identified amongst others as suppressor of cw-Inv activity. Since sequence analysis provided no information about its function, we started with the structural characterization of the protein. Transient expression of GFP fusion proteins as well as biochemical assays suggested that XopB is plasma membrane-associated. An interacting protein (NtIP1) which seems to be involved in N-myristoylation was found by yeast-two-hybrid studies and might be responsible for the membrane localization of XopB. Further tests revealed that XopB has no impact on protein secretion but might suppress basal defence.

Figure:   Schematic view of interaction between the gram-negative bacterium Xanthomonas campestris and its host plant cell. Gram-negative bacteria form a type III secretion system which is encoded by the hrp-gene cluster to inject type III effector proteins. X. campestris propagate in the apoplast and translocates app. 30 effectors into plant cells where they act to supress plant defense reaction and modulate plant metabolism to support bacterial growth. Among those we identified three effectors, namely XopB, XopJ and AvrRxv which suppress cell wall bound invertase (cw-Inv). Cw-Inv is a metabolic enzyme which serve as a marker for metabolic changes.


Project relevant publications

  • Jungkunz I, Link K, Vogel F, Voll LM, Sonnewald, S, Sonnewald U.   (2011).   AtHsp70-15 deficient Arabidopsis plants are characterized by reduced growth, a constitutive cytosolic protein response and enhanced resistance to TuMV.   Plant J. 66, 983-995.

  • 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.

  • Kocal, N., Sonnewald, U. and Sonnewald, S.   (2008).   Cell wall-bound invertase is involved in symptom development and inhibition of photosynthesis during the compatible interaction between tomato and Xanthomonas campestris pv. vesicatoria.   Plant Physiol 148, 1523-1536.

  • Essmann, J., Schmitz-Thom, I., Schön, H., Sonnewald, S., Weis, E. and Scharte, J.   (2008).   RNAi-mediated repression of cell wall invertase impairs defence in source leaves of tobacco.   Plant Physiol 147, 1288-1299.

  • Biemelt S. and Sonnewald U.   (2006).   Plant-microbe interactions to probe regulation of plant carbon metabolism.   J Plant Physiol 163, 307-318