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Comparison of Ethylene Production by Pseudomonas syringae and Ralstonia solanacearum

May 1999 , Volume 89 , Number  5
Pages  360 - 365

H. Weingart , B. Völksch , and M. S. Ullrich

First and second authors: Friedrich-Schiller-University Jena, Institute of Microbiology, Philosophenweg 12, 07743 Jena, Germany; and third author: Max-Planck-Institute of Terrestrial Microbiology, Karl-von-Frisch-Strasse, 35043 Marburg, Germany

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Accepted for publication 3 February 1999.

Strains of Pseudomonas syringae pv. pisi and Ralstonia solanacearum produced ethylene at rates 20- and 200-fold lower, respectively, than strains of P. syringae pvs. cannabina, glycinea, phaseolicola, and sesami. In the current study, we investigated which ethylene biosynthetic pathways were used by P. syringae pv. pisi and R. solanacearum. Neither the activity of an ethylene-forming enzyme nor a corresponding efe gene homolog could be detected in R. solanacearum, suggesting synthesis of ethylene via 2-keto-4-methyl-thiobutyric acid. In contrast, 2-oxoglutarate-dependent ethylene formation was observed with P. syringae pv. pisi, and Southern blot hybridization revealed the presence of an efe homolog in this pathovar. The efe genes from P. syringae pvs. cannabina, glycinea, phaseolicola, pisi, and sesami were sequenced. Nucleotide sequence comparisons indicated that the efe gene in pv. pisi was not as highly conserved as it was in other P. syringae pathovars. The pv. pisi efe homolog showed numerous nucleotide substitutions and a deletion of 13 amino acids at the C-terminus of the predicted gene product. These sequence alterations might account for the lower rate of ethylene production by this pathovar. All ethylene-producing P. syringae pathovars were virulent on bush bean plants. The overlapping host range of these pathovars suggests that horizontal transfer of the efe gene may have occurred among bacteria inhabiting the same host.

© 1999 The American Phytopathological Society