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|Title:||Phenotypic and genotypic relationship between tabtoxin production and pathogenicity in Pseudomonas syringae pv. tabaci strain PTBR2.024|
|Doctoral Committee Chair(s):||Shaw, Paul D.|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
Agriculture, Plant Pathology
|Abstract:||Pseudomonas syringae pv. tabaci strain PTBR2.024 produces tabtoxin and causes wildfire disease on tobacco and green bean. PTBR7.000, a Tn5 mutant of PTBR2.024, does not produce tabtoxin, is nonpathogenic on tobacco and is prototrophic. A 3-kb fragment from a genomic library of the parent strain PTBR2.024 complemented both mutant phenotypes. This 3-kb fragment contains two open reading frames (ORF), ORF1 and ORF2, and two truncated ORFs, ORF3 and ORF4. The Tn5 insert in PTBR7.000 was mapped to ORF2, and complementation studies showed that an intact ORF2 was sufficient to restore tabtoxin production and pathogenicity. The deduced amino acid sequences of ORF2 and truncated ORF3 contain significant homology to bacterial lysine biosynthetic enzymes, diaminopimelate decarboxylase and $\Delta\sp1$-piperidine-2,6-dicarboxylate succinyl transferase, respectively. ORF2, however, is not required for lysine biosynthesis. We designated the sequence corresponding to ORF2 as gene tabA and propose that the product of tabA is an enzyme in the tabtoxin biosynthetic pathway that recognizes a substrate analogue of a compound in the lysine biosynthetic pathway.
Another Tn5 insertion mutant of PTBR2.024, PTBR6.000, produces tabtoxin but is not pathogenic on tobacco. An 11-kb EcoRI genomic DNA fragment from PTBR2.024 restored pathogenicity to the Pat$\sp-$ mutant PTBR6.000.
A diffusible toxin restoration factor, TRF, produced by tabtoxin-producing strains restored toxin production to three independent mutants of Pseudomonas syringae pv. tabaci that are defective in tabtoxin production (Tox$\sp-$). Glutamine overcomes the inhibition produced by both PTBR2.024 and the Tox$\sp-$ mutants suggesting that the toxin produced by the Tox$\sp-$ mutants, in the presence of TRF, was tabtoxin. Genetic studies suggested that TRF is an intermediate in tabtoxin biosynthesis. Preliminary evidence indicates that TRF is a low molecular weight anionic compound that is heat labile.
|Rights Information:||Copyright 1992 Engst, Karen|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9305517|