Nature 448, 370-374 (19 July 2007) | doi:10.1038/nature05966; Received 26 April 2007; Accepted 29 May 2007

A bacterial E3 ubiquitin ligase targets a host protein kinase to disrupt plant immunity

Tracy R. Rosebrock1,2, Lirong Zeng1, Jennifer J. Brady1, Robert B. Abramovitch1,2, Fangming Xiao1 & Gregory B. Martin1,2

  1. Boyce Thompson Institute for Plant Research, Tower Road, Ithaca, New York 14853, USA
  2. Department of Plant Pathology, Cornell University, Ithaca, New York 14853, USA

Correspondence to: Gregory B. Martin1,2 Correspondence and requests for materials should be addressed to G.B.M. (Email: gbm7@cornell.edu).

Many bacterial pathogens of plants and animals use a type III secretion system to deliver diverse virulence-associated 'effector' proteins into the host cell1. The mechanisms by which these effectors act are mostly unknown; however, they often promote disease by suppressing host immunity2. One type III effector, AvrPtoB, expressed by the plant pathogen Pseudomonas syringae pv. tomato, has a carboxy-terminal domain that is an E3 ubiquitin ligase3. Deletion of this domain allows an amino-terminal region of AvrPtoB (AvrPtoB1–387) to be detected by certain tomato varieties leading to immunity-associated programmed cell death4. Here we show that a host kinase, Fen, physically interacts with AvrPtoB1–387 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 AvrPtoB1–387 and not to full-length AvrPtoB. Thus, by acquiring an E3 ligase domain, AvrPtoB has thwarted a highly conserved host resistance mechanism.

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