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J. Bacteriol., 04 1997, 2247-2258, Vol 179, No. 7
JJ Rich and DK Willis
A mutational analysis of lesion-forming ability was undertaken in
Pseudomonas syringae pv. syringae B728a, causal agent of bacterial brown
spot disease of bean. Following a screen of 6,401 Tn5-containing
derivatives of B728a on bean pods, 26 strains that did not form disease
lesions were identified. Nine of the mutant strains were defective in the
ability to elicit the hypersensitive reaction (HR) and were shown to
contain Tn5 insertions within the P. syringae pv. syringae hrp region. Ten
HR+ mutants were defective in the production of the toxin syringomycin, and
a region of the chromosome implicated in the biosynthesis of syringomycin
was deleted in a subset of these mutants. The remaining seven
lesion-defective mutants retained the ability to produce protease and
syringomycin. Marker exchange mutagenesis confirmed that the Tn5 insertion
was causal to the mutant phenotype in several lesion-defective, HR+
strains. KW239, a lesion- and syringomycin-deficient mutant, was
characterized at the molecular level. Sequence analysis of the chromosomal
region flanking the Tn5 within KW239 revealed strong similarities to a
number of known Escherichia coli gene products and DNA sequences: the nusA
operon, including the complete initiator tRNA(Met) gene, metY; a tRNA(Leu)
gene; the tpiA gene product; and the MrsA protein. Removal of sequences
containing the two potential tRNA genes prevented restoration of mutant
KW239 in trans. The Tn5 insertions within the lesion-deficient strains
examined, including KW239, were not closely linked to each other or to the
lemA or gacA genes previously identified as involved in lesion formation by
P. syringae pv. syringae.
Copyright © 1997, American Society for Microbiology
Multiple loci of Pseudomonas syringae pv. syringae are involved in pathogenicity on bean: restoration of one lesion-deficient mutant requires two tRNA genes
Department of Plant Pathology, University of Wisconsin-Madison, 53706, USA.
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