title: A bacterial E3 ubiquitin ligase targets a host protein kinase to disrupt plant immunity.
abstract: Many bacterial pathogens of plants and animals use a type III secretion system to deliver diverse virulence-associated 'effector' proteins into the host cell. The mechanisms by which these effectors act are mostly unknown; however, they often promote disease by suppressing host immunity. One type III effector, AvrPtoB, expressed by the plant pathogen Pseudomonas syringae pv. tomato, has a carboxy-terminal domain that is an E3 ubiquitin ligase. Deletion of this domain allows an amino-terminal region of AvrPtoB (AvrPtoB(1-387)) to be detected by certain tomato varieties leading to immunity-associated programmed cell death. Here we show that a host kinase, Fen, physically interacts with AvrPtoB(1-387 )and is responsible for activating the plant immune response. The AvrPtoB E3 ligase specifically ubiquitinates Fen and promotes its degradation in a proteasome-dependent manner. This degradation leads to disease susceptibility in Fen-expressing tomato lines. Various wild species of tomato were found to exhibit immunity in response to AvrPtoB(1-387 )and not to full-length AvrPtoB. Thus, by acquiring an E3 ligase domain, AvrPtoB has thwarted a highly conserved host resistance mechanism.
authors.affiliation: Boyce Thompson Institute for Plant Research, Tower Road, Ithaca, New York 14853, USA.
authors.forename: Tracy R
authors.initials: TR
authors.lastname: Rosebrock
authors.forename: Lirong
authors.initials: L
authors.lastname: Zeng
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: Brady
authors.forename: Robert B
authors.initials: RB
authors.lastname: Abramovitch
authors.forename: Fangming
authors.initials: F
authors.lastname: Xiao
authors.forename: Gregory B
authors.initials: GB
authors.lastname: Martin
mesh_terms: D018551:Solanum lycopersicum / Q000145:classification / Q000201:enzymology / Q000276:immunology* / Q000382:microbiology*; D010641:Phenotype; D010935:Plant Diseases / Q000276:immunology* / Q000382:microbiology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D044224:Pseudomonas syringae / Q000201:enzymology* / Q000276:immunology; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000378:metabolism*
chemical_list: D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; D011494:Protein Kinases; D046988:Proteasome Endopeptidase Complex