9219200 Quigley The research described in this proposal will investigate the mechanism of secretion of syringomycin by the plant pathogenic bacterium, Pseudomonas syringae pathovar syringae. Strains of this bacterium cause disease in a wide range of important crop plant species. Virtually all of the pathogenic strains of P. s. syringae produce syringae produce syringomycin, which is a potent phytotoxin related to the polypeptin class of peptide antibiotics. The syrD gene of P. s. syringae is required for the production of syringomycin, and its predicted product, SyrD, has strong homology with proteins in the ATP-binding cassette (ABC) transporter family, and it carries all of the key sequence and structural features required for function by ABC proteins. Preliminary experiments have demonstrated that the syrD gene is restricted to pathovar syringae strains of P. syringae. It is proposed that SyrD gene is restricted to pathovar syringae strains of P. syringae. It is proposed that SyrD is an inner membrane protein that functions as the pivotal translator in the secretion of syringomycin by P.s. syringae. Objectives of this project are: 1) to determine of SyrD is a membrane protein that functions as an ABC transporter protein in syringomycin secretion. 2) To determine if the syrD holologs in strains of P. s syringae that produce analogs of syringomycin encode SyrD proteins that are functionally interchangeable. 3) to identify and genetically analyze other protein components of the syringomycin export apparatus. %%% This research is significant because (i) syringomycin is an important virulence determinant in diseases caused by P. s syringae (ii) secretion of syringomycin by an ABC transporter mechanism involving SyrD would represent the first demonstration of such a system in toxin production by any plant pathogen, and would establish SyrD as the first known protein for bacterial phytotoxin secretion, and (iii) the mechanisms of lipopeptide antibiotic sec retion is largely unknown, reflecting the poor knowledge of the secretion mechanism for bacterial antibiotics in general. Further analysis of SyrD could provide important knowledge about the secretion of lipopeptide antibiotics produced by medically and agriculturally important bacterial pathogens. ***
