First and third authors: National Institute of Sericultural and Entomological Science, Tsukuba, Ibaraki 305-8634, Japan; and second author: Kumamoto Institute of Technology, Ikeda, Kumamoto 860-0082, Japan
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Accepted for publication 9 August 1998.
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.
polymerase chain reaction
© 1998 The American Phytopathological Society