Bacterial pathogens of plants and animals utilize conserved type III delivery systems to traffic effector proteins into host cells. Plant innate immune systems evolved disease resistance (R) genes to recognize some type III effectors, termed avirulence (Avr) proteins. On disease-susceptible (r) plants, Avr proteins can contribute to pathogen virulence. We demonstrate that several type III effectors from Pseudomonas syringae are targeted to the host plasma membrane and that efficient membrane association enhances function. Efficient localization of three Avr proteins requires consensus myristoylation sites, and Avr proteins can be myristoylated inside the host cell. These prokaryotic type III effectors thus utilize a eukaryote-specific posttranslational modification to access the subcellular compartment where they function.
Bibliographical noteFunding Information:
This research is supported by DOE Grant DE-FG05–95ER20187 to J. L. D., NIH-NRSA Fellowship F32GM17612 to S. K., and NSF Grant MCB-9604830 to F. K. We thank Drs. Ulla Bonas, Alan Collmer, and John Mansfield for gifts of strains and reagents. We thank Jen Sheen for GFP constructs, and Chere Petty for assistance with confocal microscopy. Experimental Fu provided by Ben F. Holt III and Dr. Petra Epple.