title: Multiple Xanthomonas euvesicatoria Type III Effectors Inhibit flg22-Triggered Immunity.
abstract: Xanthomonas euvesicatoria is the causal agent of bacterial spot disease in pepper and tomato. X. euvesicatoria bacteria interfere with plant cellular processes by injecting effector proteins into host cells through the type III secretion (T3S) system. About 35 T3S effectors have been identified in X. euvesicatoria 85-10, and a few of them were implicated in suppression of pattern-triggered immunity (PTI). We used an Arabidopsis thaliana pathogen-free protoplast-based assay to identify X. euvesicatoria 85-10 effectors that interfere with PTI signaling induced by the bacterial peptide flg22. Of 33 tested effectors, 17 inhibited activation of a PTI-inducible promoter. Among them, nine effectors also interfered with activation of an abscisic acid-inducible promoter. However, effectors that inhibited flg22-induced signaling did not affect phosphorylation of mitogen-activated protein (MAP) kinases acting downstream of flg22 perception. Further investigation of selected effectors revealed that XopAJ, XopE2, and XopF2 inhibited activation of a PTI-inducible promoter by the bacterial peptide elf18 in Arabidopsis protoplasts and by flg22 in tomato protoplasts. The effectors XopF2, XopE2, XopAP, XopAE, XopH, and XopAJ inhibited flg22-induced callose deposition in planta and enhanced disease symptoms caused by attenuated Pseudomonas syringae bacteria. Finally, selected effectors were found to localize to various plant subcellular compartments. These results indicate that X. euvesicatoria bacteria utilize multiple T3S effectors to suppress flg22-induced signaling acting downstream or in parallel to MAP kinase cascades and suggest they act through different molecular mechanisms.
authors.affiliation: 1 Department of Molecular Biology and Ecology of Plants, Tel-Aviv University, 69978 Tel-Aviv, Israel; and.
authors.forename: Georgy
authors.initials: G
authors.lastname: Popov
authors.affiliation: 2 Department of Biochemistry, Centre for Plant Molecular Biology, Eberhard Karls University, Auf der Morgenstelle 32, D-72076 Tübingen, Germany.
authors.forename: Malou
authors.initials: M
authors.lastname: Fraiture
authors.affiliation: 2 Department of Biochemistry, Centre for Plant Molecular Biology, Eberhard Karls University, Auf der Morgenstelle 32, D-72076 Tübingen, Germany.
authors.forename: Frederic
authors.initials: F
authors.lastname: Brunner
authors.affiliation: 1 Department of Molecular Biology and Ecology of Plants, Tel-Aviv University, 69978 Tel-Aviv, Israel; and.
authors.forename: Guido
authors.initials: G
authors.lastname: Sessa
mesh_terms: D017360:Arabidopsis / Q000276:immunology* / Q000382:microbiology; D005408:Flagellin / Q000037:antagonists & inhibitors*; D017930:Genes, Reporter; D005936:Glucans / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010935:Plant Diseases / Q000276:immunology* / Q000382:microbiology; D011401:Promoter Regions, Genetic / Q000235:genetics; D011523:Protoplasts; D044224:Pseudomonas syringae / Q000472:pathogenicity; D015398:Signal Transduction; D000069296:Type III Secretion Systems / Q000235:genetics / Q000378:metabolism*; D014974:Xanthomonas / Q000235:genetics* / Q000276:immunology / Q000472:pathogenicity
chemical_list: D005936:Glucans; D000069296:Type III Secretion Systems; D005408:Flagellin; C048306:callose; D020928:Mitogen-Activated Protein Kinases