The Xanthomonas type-III effector XopS interferes with proteasomal turnover of a WRKY transcription factor to dampen the induction of plant defense responses
F. BÖRNKE (1), S. Üstün (1), D. van Thiel (1) (1) Leibniz-Institute for Vegetable and Ornamental Crops, Germany

We show here that the type-III effector (T3E) proteins XopS of Xanthomonas campestris pv.vesicatoria, causal agent of bacterial spot of pepper, interacts inside the plant cell nucleus with a protein pair consisting of the transcription factor WRKY40 and an E3-ubiquitin ligase. The E3 ligase interacts with WRKY40 in vitro and in planta and ubiquitinates the transcription factor in vitro. Accordingly, transient expression in leaves of Nicotiana benthamiana suggests that WRKY40 undergoes rapid proteasomal protein turnover. However, WRKY40 protein strongly accumulates upon co-expression with XopS, indicating that XopS interferes with proteasomal turnover of WRKY40 and thus could interfere with defense gene induction that requires degradation of this negative regulator of plant defense. WRKY40 target genes in pepper have not yet been identified; however, inferred from the information available for Arabidopsis WRKY40 target genes we have analyzed the expression of EDS1 and JAZ8 during infection of pepper with Xanthomonas wild type or a xopS deletion strain. A significant increase in mRNA level of both genes could be observed in tissue infected with the XopS deletion strain, suggesting that this T3E is required to prevent the induction of WRKY40 target genes during Xanthomonas infection of susceptible pepper plants. A possible mechanism by which XopS interferes with proteasomal turnover of WRKY40 is discussed.

Abstract Number: P9-241
Session Type: Poster