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Bacterial Effector HopF2 Suppresses Arabidopsis Innate Immunity at the Plasma Membrane

May 2011 , Volume 24 , Number  5
Pages  585 - 593

Shujing Wu,1 Dongping Lu,2 Mehdi Kabbage,1 Hai-Lei Wei,3 Bryan Swingle,4,3 Angela R. Records,1 Martin Dickman,1 Ping He,2 and Libo Shan1

1Department of Plant Pathology and Microbiology and 2Department of Biochemistry and Biophysics, and Institute for Plant Genomics and Biotechnology, Texas A&M University, College Station, TX 77843, U.S.A.; 3Department of Plant Pathology and Plant-Microbe Biology, Cornell University, and 4United States Department of Agriculture-Agricultural Research Service, Ithaca, NY 14853, U.S.A.

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Accepted 27 December 2010.

Many bacterial pathogens inject a cocktail of effector proteins into host cells through type III secretion systems. These effectors act in concert to modulate host physiology and immune signaling, thereby promoting pathogenicity. In a search for additional Pseudomonas syringae effectors in suppressing plant innate immunity triggered by pathogen or microbe-associated molecular patterns (PAMPs or MAMPs), we identified P. syringae tomato DC3000 effector HopF2 as a potent suppressor of early immune-response gene transcription and mitogen-activated protein kinase (MAPK) signaling activated by multiple MAMPs, including bacterial flagellin, elongation factor Tu, peptidoglycan, lipopolysaccharide and HrpZ1 harpin, and fungal chitin. The conserved surface-exposed residues of HopF2 are essential for its MAMP suppression activity. HopF2 is targeted to the plant plasma membrane through a putative myristoylation site, and the membrane association appears to be required for its MAMP-suppression function. Expression of HopF2 in plants potently diminished the flagellin-induced phosphorylation of BIK1, a plasma membrane–associated cytoplasmic kinase that is rapidly phosphorylated within one minute upon flagellin perception. Thus, HopF2 likely intercepts MAMP signaling at the plasma membrane immediately of signal perception. Consistent with the potent suppression function of multiple MAMP signaling, expression of HopF2 in transgenic plants compromised plant nonhost immunity to bacteria P. syringae pv. Phaseolicola and plant immunity to the necrotrophic fungal pathogen Botrytis cinerea.

© 2011 The American Phytopathological Society