HrpZ(Psph) from the plant pathogen Pseudomonas syringae pv. phaseolicola binds to lipid bilayers and forms an ion-conducting pore in vitro

The hrp gene clusters of plant pathogenic bacteria control pathogenicity on their host plants and ability to elicit the hypersensitive reaction in res istant plants. Some hrp gene products constitute elements of the type III s ecretion system, by which effector proteins are exported and delivered into plant cells. Here, we show that the hrpZ gene product from the bean halo-b light pathogen, Pseudomonas syringae pv. phaseolicola (HrpZ(Psph)), is secr eted in an hrp-dependent manner in P. syringae pv, phaseolicola and exporte d by the type III secretion system in the mammalian pathogen Yersinia enter ocolitica, HrpZ(Psph) was found to associate stably with liposomes and synt hetic bilayer membranes. Under symmetric ionic conditions, addition of 2 nM of purified recombinant HrpZ(Psph) to the cis compartment of planar lipid bilayers provoked an ion current with a large unitary conductivity of 207 p S. HrpZ(Psph)-related proteins from P, syringae pv. tomato or syringae trig gered ion currents similar to those stimulated by HrpZ(Psph). The HrpZ(Psph )-mediated ion-conducting pore was permeable for cations but did not mediat e fluxes of Cl-. Such pore-forming activity may allow nutrient release and/ or delivery of virulence factors during bacterial colonization of host plan ts.