high-throughput, near-saturating screen for type III effector genes from Pseudomonas syringae.
Proc. Natl. Acad. Sci., USA 102, 2549-2554
Chang, JH, JM Urbach, TF Law, LW Arnold, A Hu, S Gombar, SR Grant, FM Ausubel and JL Dangl
Summary
"Pseudomonas syringae strains deliver variable numbers of type IIIeffector proteins into plant cells during infection. These proteinsare required for virulence, because strains incapable of deliveringthem are nonpathogenic. We implemented a whole-genome, highthroughputscreen for identifying P. syringae type III effectorgenes. The screen relied on FACS and an arabinose-inducible hrpL_ factor to automate the identification and cloning of HrpLregulatedgenes. We determined whether candidate genes encodetype III effector proteins by creating and testing full-length proteinfusions to a reporter called _79AvrRpt2 that, when fused to knowntype III effector proteins, is translocated and elicits a hypersensitiveresponse in leaves of Arabidopsis thaliana expressing the RPS2plant disease resistance protein. _79AvrRpt2 is thus a marker fortype III secretion system-dependent translocation, the most criticalcriterion for defining type III effector proteins. We describe ourscreen and the collection of type III effector proteins from twopathovars of P. syringae. This stringent functional criteria defined29 type III proteins from P. syringae pv. tomato, and 19 from P.syringae pv. phaseolicola race 6. Our data provide full functionalannotation of the hrpL-dependent type III effector suites from twosequenced P. syringae pathovars and show that type III effectorprotein suites are highly variable in this pathogen, presumablyreflecting the evolutionary selection imposed by the various hostplants."