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A Conjugative Plasmid Carrying the efe Gene for the Ethylene-Forming Enzyme Isolated from Pseudomonas syringae pv. glycinea

Previous work suggested that the efe gene encoding the ethylene-forming enzyme was present in the plasmids of three pathovars of Pseudomonas syringae including glycinea, phaseolicola (kudzu strains), and cannabina. However, no direct evidence to support this assumption had been presented. In the current study, we isolated the conjugative plasmid harboring the efe gene (ethylene plasmid) designated pETH2 from P. syringae pv. glycinea MAFF301683. pETH2 was detected by Southern blot hybridization using the efe probe, marked with the transposon mini-Tn5-Km1, and transferred into P. syringae Ni27ⁿ, which does not produce ethylene. The transconjugant Ni27ⁿ (pETH2) produced ethylene at a level similar to pv. glycinea MAFF301683. In addition, the plasmid designated pCOR2, which encodes coronatine biosynthesis genes, was detected in the same strain. Although the molecular size of the plasmid pCOR2 was not easily distinguishable from pETH2, pCOR2 transferred independently into Ni27ⁿ and the transconjugants produced coronatine. These findings suggested that the efe gene has been horizontally dispersed among pathovars of P. syringae by plasmid-mediated conjugation in nature.