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A Pathogenicity Gene Isolated from the pPATH Plasmid of Erwinia herbicola pv. gypsophilae Determines Host Specificity

August 1998 , Volume 11 , Number  8
Pages  753 - 762

Lea Valinsky , 1 , 2 Shulamit Manulis , 1 Roni Nizan , 2 David Ezra , 1 , 2 and Isaac Barash 2

1Department of Plant Pathology, ARO, The Volcani Center, P.O.B. 6, Bet Dagan 50250; and 2Department of Plant Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel

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Accepted 15 April 1998.

The host range of the gall-forming bacterium Erwinia herbicola pv. gypsophilae (Ehg) is restricted to the gypsophila plant whereas E. herbicola pv. betae (Ehb) incites galls on beet as well as gypsophila. The pathogenicity of Ehg and Ehb was previously shown to be dependent on a plasmid (pPATH). Transposon mutagenesis was used to generate mutants on the cosmid pLA150 of the pPATH from Ehg824-1. A cluster of nonpathogenic mutations flanked by two IS1327 elements was identified on a 3.2-kb NdeI DNA fragment. All mutants were restored to pathogenicity by complementation in trans with the wild-type Ehg DNA. DNA sequence analysis of the 3.2-kb NdeI fragment revealed a single open reading frame (ORF) of 2 kb as well as a potential ribosome binding site and a putative hrp box upstream to the ORF. The ORF had no significant homology to known genes. Southern analysis also revealed the presence of DNA sequences that hybridized to the ORF in the beet pathovar Ehb4188. This gene was isolated and sequenced. Marker exchange mutants generated in the ORF of Ehb eliminated the pathogenicity of Ehb on gypsophila but fully retained its pathogenicity on beet. Since the putative gene appeared to encode a host-specific virulence factor for gypsophila it was designated as hsvG.

Additional keywords: type III secretion system.

© 1998 The American Phytopathological Society