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 resistant plants. Some hrp gene products constitute elements of the type III secretion system, by which effector proteins are exported and delivered into plant cells. Here, we show that the hrpZ gene product from the bean halo-blight pathogen, Pseudomonas syringae pv. phaseolicola (HrpZ(Psph)), is secreted in an hrp-dependent manner in P. syringae pv. phaseolicola and exported by the type III secretion system in the mammalian pathogen Yersinia enterocolitica. HrpZ(Psph) was found to associate stably with liposomes and synthetic 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 pS. HrpZ(Psph)-related proteins from P. syringae pv. tomato or syringae triggered ion currents similar to those stimulated by HrpZ(Psph). The HrpZ(Psph)-mediated ion-conducting pore was permeable for cations but did not mediate fluxes of Cl-. Such pore-forming activity may allow nutrient release and/or delivery of virulence factors during bacterial colonization of host plants.