JB Accepts, published online ahead of print on 8 February 2008

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J. Bacteriol. doi:10.1128/JB.01702-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The HopZ family of Pseudomonas syringae type III effectors require myristoylation for virulence and avirulence functions in Arabidopsis

Jennifer D. Lewis, Wasan Abada, Wenbo Ma, David S. Guttman, and Darrell Desveaux^*

Department of Cell & Systems Biology, University of Toronto, 25 Willcocks St., Toronto, ON M5S3B2, Canada; Department of Plant Pathology and Microbiology, University of California, Riverside, 900 University Ave, Riverside, CA 92521, USA; Centre for the Analysis of Genome Evolution & Function, University of Toronto

^* To whom correspondence should be addressed. Email: desveaux{at}csb.utoronto.ca.

Pseudomonas syringae utilizes the type III secretion system to translocate effector proteins into plant cells where they can contribute to the pathogen's ability to infect and cause disease. Recognition of these effectors by resistance proteins induces defense responses that typically include a programmed cell death reaction called the hypersensitive response. The YopJ/HopZ family of type III effector proteins is a common family of effector proteins found in animal and plant pathogenic bacteria. The HopZ family in P. syringae includes HopZ1a_PsyA2, HopZ1b_PgyUnB647, HopZ1c_PmaES4326, HopZ2_Ppi895A and HopZ3_PsyB728a. HopZ1a is predicted to be most similar to the ancestral HopZ allele and causes a hypersensitive response in multiple plant species including Arabidopsis thaliana. It has therefore been proposed that host defense responses have driven the diversification of this effector family. In this study, we further characterize the hypersensitive response induced by HopZ1a and demonstrate that it is not dependent on known resistance genes. Further, we identify a novel virulence function for HopZ2 that requires the catalytic cysteine demonstrated to be required for protease activity. Sequence analysis of the HopZ family reveals the presence of a predicted myristoylation sequence in all members except HopZ3. We demonstrate that the myristoylation site is required for membrane localization of this effector family and contributes to the virulence and avirulence activity of HopZ2 and HopZ1a, respectively. This study provides insight into the selective pressures driving virulence protein evolution by presenting a detailed functional characterization of the diverse HopZ family of type III effectors on the model plant Arabidopsis.

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