Syringomycin is a peptide phytotoxin produced by the bacterium, Pseudomonas syringae pv. syringae. The toxin is a major virulence factor in many plant and crop diseases. Previous work supported by NSF showed that syringomycin's primary site of action is the host plasma membrane. Several plasma membrane- associated events caused by syringomycin were demonstrated including changes in K+ efflux, Ca2+ influx, H+-pump ATPase activity, membrane charge potential, and protein phosphorylation. Also, the structure of syringomycin was determined. Further studies on the mechanism of action of the syringomycin are being pursued. The studies exploit the action of the toxin on the yeast Saccharomyces cerevisiae. Preliminary studies revealed that syringomycin affects S. cerevisiae in ways which resemble its effects on plant plasma membranes. Syringomycin-resistant, temperature-sensitive mutants are being isolated and characterized. The normal versions of the defective genes are being isolated by gene complementation techniques and characterized. These genes encode proteins that function in the syringomycin response pathway. Revertants with second-site suppressor mutations are being studied to determine how the identified gene products interact in the syringomycin response pathway. This project is significant because it determines how an important, ubiquitous bacterial phytotoxin causes plant disease and provides basic information about the function, structure and regulation of the plant cell plasma membrane.
