title: The Pseudomonas syringae type III effector AvrRpt2 functions downstream or independently of SA to promote virulence on Arabidopsis thaliana.
abstract: AvrRpt2, a Pseudomonas syringae type III effector protein, functions from inside plant cells to promote the virulence of P. syringae pv. tomato strain DC3000 (PstDC3000) on Arabidopsis thaliana plants lacking a functional copy of the corresponding RPS2 resistance gene. In this study, we extended our understanding of AvrRpt2 virulence activity by exploring the hypothesis that AvrRpt2 promotes PstDC3000 virulence by suppressing plant defenses. When delivered by PstDC3000, AvrRpt2 suppresses pathogen-related (PR) gene expression during infection, suggesting that AvrRpt2 suppresses defenses mediated by salicylic acid (SA). However, AvrRpt2 promotes PstDC3000 growth on transgenic plants expressing the SA-degrading enzyme NahG, indicating that AvrRpt2 does not promote bacterial virulence by modulating SA levels during infection. AvrRpt2 general virulence activity does not depend on the RPM1 resistance gene, as mutations in RPM1 had no effect on AvrRpt2-induced phenotypes. Transgenic plants expressing AvrRpt2 displayed enhanced susceptibility to PstDC3000 strains defective in type III secretion, indicating that enhanced susceptibility of these plants is not because of suppression of defense responses elicited by other type III effectors. Additionally, avrRpt2 transgenic plants did not exhibit increased susceptibility to Peronospora parasitica and Erysiphe cichoracearum, suggesting that AvrRpt2 virulence activity is specific to P. syringae.
authors.affiliation: Department of Biology, Washington University in St Louis, St Louis, MO 63130, USA.
authors.forename: Zhongying
authors.initials: Z
authors.lastname: Chen
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Kloek
authors.forename: Alayne
authors.initials: A
authors.lastname: Cuzick
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Moeder
authors.forename: Dingzhong
authors.initials: D
authors.lastname: Tang
authors.forename: Roger W
authors.initials: RW
authors.lastname: Innes
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Klessig
authors.forename: John M
authors.initials: JM
authors.lastname: McDowell
authors.forename: Barbara N
authors.initials: BN
authors.lastname: Kunkel
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism / Q000382:microbiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D005658:Fungi / Q000254:growth & development; D015964:Gene Expression Regulation, Bacterial; D018506:Gene Expression Regulation, Plant; D007113:Immunity, Innate / Q000235:genetics; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D044742:Peronospora / Q000254:growth & development; D010935:Plant Diseases / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D044224:Pseudomonas syringae / Q000472:pathogenicity*; D020156:Salicylic Acid / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics; D014774:Virulence / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D010940:Plant Proteins; C095014:RPM1 protein, Arabidopsis; C089426:RPS2 protein, Arabidopsis; C420919:avrRpt2 protein, Pseudomonas syringae; C053376:pathogenesis-related proteins, plant; D006899:Mixed Function Oxygenases; C022619:salicylate 1-monooxygenase; D020156:Salicylic Acid