The chlorosis-inducing phytotoxin coronatine has an unusual structure and consists of a polyketide component joined to an ethylcyclopropyl ring. In contrast to other phytotoxins produced by Pseudomonas syringae, coronatine is produced by multiple pathovars with distinct host specificity. Despite the importance of coronatine in the virulence of producing pathovars the genetics of coronatine biosynthesis has not been systematically studied. Transposon mutagenesis was used to generate coronatine- defective mutants of P. syringae pv. tomato. The physical analysis of these mutants suggested the involvement of a 101 kb plasmid (designated pPT23A) in coronatine synthesis. pPT23A was subsequently transferred into P. syringae pv. syringae PS61, a nonproducer of coronatine. Upon acquisition of pPT23A, PS61 gained the ability to make coronatine. Therefore, conclusive evidence has been collected for the involvement of plasmid pPT23A in production of coronatine. The experiments outlined in this proposal will precisely define the regions of pPT23A involved in coronatine biosynthesis by moleuclar cloning, mutagenesis, and complementation experiments. The results of these proposed experiments will advance knowledge in the area of phytotoxin genetics.
