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Publications - Stress and Develop Biology

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Publications

Singer, A. U.; Schulze, S.; Skarina, T.; Xu, X.; Cui, H.; Eschen-Lippold, L.; Egler, M.; Srikumar, T.; Raught, B.; Lee, J.; Scheel, D.; Savchenko, A.; Bonas, U.; A Pathogen Type III Effector with a Novel E3 Ubiquitin Ligase Architecture PLOS Pathog. 9, e1003121, (2013) DOI: 10.1371/journal.ppat.1003121

Type III effectors are virulence factors of Gram-negative bacterial pathogens delivered directly into host cells by the type III secretion nanomachine where they manipulate host cell processes such as the innate immunity and gene expression. Here, we show that the novel type III effector XopL from the model plant pathogen Xanthomonas campestris pv. vesicatoria exhibits E3 ubiquitin ligase activity in vitro and in planta, induces plant cell death and subverts plant immunity. E3 ligase activity is associated with the C-terminal region of XopL, which specifically interacts with plant E2 ubiquitin conjugating enzymes and mediates formation of predominantly K11-linked polyubiquitin chains. The crystal structure of the XopL C-terminal domain revealed a single domain with a novel fold, termed XL-box, not present in any previously characterized E3 ligase. Mutation of amino acids in the central cavity of the XL-box disrupts E3 ligase activity and prevents XopL-induced plant cell death. The lack of cysteine residues in the XL-box suggests the absence of thioester-linked ubiquitin-E3 ligase intermediates and a non-catalytic mechanism for XopL-mediated ubiquitination. The crystal structure of the N-terminal region of XopL confirmed the presence of a leucine-rich repeat (LRR) domain, which may serve as a protein-protein interaction module for ubiquitination target recognition. While the E3 ligase activity is required to provoke plant cell death, suppression of PAMP responses solely depends on the N-terminal LRR domain. Taken together, the unique structural fold of the E3 ubiquitin ligase domain within the Xanthomonas XopL is unprecedented and highlights the variation in bacterial pathogen effectors mimicking this eukaryote-specific activity.
Publications

Schulze, S.; Kay, S.; Büttner, D.; Egler, M.; Eschen-Lippold, L.; Hause, G.; Krüger, A.; Lee, J.; Müller, O.; Scheel, D.; Szczesny, R.; Thieme, F.; Bonas, U.; Analysis of new type III effectors from Xanthomonas uncovers XopB and XopS as suppressors of plant immunity New Phytol. 195, 894-911, (2012) DOI: 10.1111/j.1469-8137.2012.04210.x

The pathogenicity of the Gram‐negative plant‐pathogenic bacterium Xanthomonas campestris pv. vesicatoria (Xcv) is dependent on type III effectors (T3Es) that are injected into plant cells by a type III secretion system and interfere with cellular processes to the benefit of the pathogen.In this study, we analyzed eight T3Es from Xcv strain 85‐10, six of which were newly identified effectors. Genetic studies and protoplast expression assays revealed that XopB and XopS contribute to disease symptoms and bacterial growth, and suppress pathogen‐associated molecular pattern (PAMP)‐triggered plant defense gene expression.In addition, XopB inhibits cell death reactions induced by different T3Es, thus suppressing defense responses related to both PAMP‐triggered immunity (PTI) and effector‐triggered immunity (ETI).XopB localizes to the Golgi apparatus and cytoplasm of the plant cell and interferes with eukaryotic vesicle trafficking. Interestingly, a XopB point mutant derivative was defective in the suppression of ETI‐related responses, but still interfered with vesicle trafficking and was only slightly affected with regard to the suppression of defense gene induction. This suggests that XopB‐mediated suppression of PTI and ETI is dependent on different mechanisms that can be functionally separated.
Publications

Eschen-Lippold, L.; Landgraf, R.; Smolka, U.; Schulze, S.; Heilmann, M.; Heilmann, I.; Hause, G.; Rosahl, S.; Activation of defense against Phytophthora infestans in potato by down-regulation of syntaxin gene expression New Phytol. 193, 985-996, (2012) DOI: 10.1111/j.1469-8137.2011.04024.x

• The oomycete Phytophthora infestans is the causal agent of late blight, the most devastating disease of potato. The importance of vesicle fusion processes and callose deposition for defense of potato against Phytophthora infestans was analyzed.• Transgenic plants were generated, which express RNA interference constructs targeted against plasma membrane‐localized SYNTAXIN‐RELATED 1 (StSYR1) and SOLUBLE N‐ETHYLMALEIMIDE‐SENSITIVE FACTOR ADAPTOR PROTEIN 33 (StSNAP33), the potato homologs of Arabidopsis AtSYP121 and AtSNAP33, respectively.• Phenotypically, transgenic plants grew normally, but showed spontaneous necrosis and chlorosis formation at later stages. In response to infection with Phytophthora infestans, increased resistance of StSYR1‐RNAi plants, but not StSNAP33‐RNAi plants, was observed. This increased resistance correlated with the constitutive accumulation of salicylic acid and PR1 transcripts. Aberrant callose deposition in Phytophthora infestans‐infected StSYR1‐RNAi plants coincided with decreased papilla formation at penetration sites. Resistance against the necrotrophic fungus Botrytis cinerea was not significantly altered. Infiltration experiments with bacterial solutions of Agrobacterium tumefaciens and Escherichia coli revealed a hypersensitive phenotype of both types of RNAi lines.• The enhanced defense status and the reduced growth of Phytophthora infestans on StSYR1‐RNAi plants suggest an involvement of syntaxins in secretory defense responses of potato and, in particular, in the formation of callose‐containing papillae.
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