title: The Pseudomonas syringae type III effector HopAM1 enhances virulence on water-stressed plants.
abstract: Pseudomonas syringae strains deliver diverse type III effector proteins into host cells, where they can act as virulence factors. Although the functions of the majority of type III effectors are unknown, several have been shown to interfere with plant basal defense mechanisms. Type III effectors also could contribute to bacterial virulence by enhancing nutrient uptake and pathogen adaptation to the environment of the host plant. We demonstrate that the type III effector HopAM1 (formerly known as AvrPpiB) enhances the virulence of a weak pathogen in plants that are grown under drought stress. This is the first report of a type III effector that aids pathogen adaptation to water availability in the host plant. Expression of HopAM1 makes transgenic Ws-0 Arabidopsis hypersensitive to abscisic acid (ABA) for stomatal closure and germination arrest. Conditional expression of HopAM1 in Arabidopsis also suppresses basal defenses. ABA responses overlap with defense responses and ABA has been shown to suppress defense against P. syringae pathogens. We propose that HopAM1 aids P. syringae virulence by manipulation of ABA responses that suppress defense responses. In addition, host ABA responses enhanced by type III delivery of HopAM1 protect developing bacterial colonies inside leaves from osmotic stress.
authors.affiliation: Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA.
authors.forename: Ajay K
authors.initials: AK
authors.lastname: Goel
authors.forename: Derek
authors.initials: D
authors.lastname: Lundberg
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Torres
authors.forename: Ryan
authors.initials: R
authors.lastname: Matthews
authors.forename: Chiharu
authors.initials: C
authors.lastname: Akimoto-Tomiyama
authors.forename: Lisa
authors.initials: L
authors.lastname: Farmer
authors.forename: Jeffery L
authors.initials: JL
authors.lastname: Dangl
authors.forename: Sarah R
authors.initials: SR
authors.lastname: Grant
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D029681:Arabidopsis Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D009997:Osmotic Pressure; D030821:Plants, Genetically Modified; D044224:Pseudomonas syringae / Q000472:pathogenicity*; D014774:Virulence; D037521:Virulence Factors / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D037521:Virulence Factors; D000040:Abscisic Acid