Pseudomonas syringae pv. phaseolicola genomic clones harboring heterologous DNA sequences suppress the same phaseolotoxin-deficient mutants.

Abstract

Cosmid cloning and mutagenesis were used to identify genes involved in the production of phaseolotoxin, the chlorosis-inducing phytotoxin of Pseudomonas syringae pv. phaseolicola, the causal agent of halo blight of bean (Phaseolus vulgaris L.). Eight stable clones were isolated from a genomic cosmid library by en masse mating to 10 ethyl methanesulfonate (EMS)-induced Tox- mutants. In cross-matings, each suppressed all 10 mutants as well as an additional 70 EMS-induced Tox- mutants (and one UV-induced Tox- mutant). On the basis of restriction endonuclease analysis and hybridization studies, the clones were grouped into three classes. Clones in a particular class shared common fragments, whereas clones in different classes did not. Clones from class I (but not classes II and III) also suppressed Tn5-induced Tox- mutants. Interposon mutagenesis and marker exchange of a representative clone from class III into the wild-type genome did not alter its Tox+ phenotype, indicating that this clone does not harbor structural or regulatory genes involved in phaseolotoxin production. We suggest that the genome of P. syringae pv. phaseolicola contains a "hot spot" in one of the functions involved in toxin production which is affected by EMS and UV and that heterologous clones are able to suppress the Tox- phenotype because their inserts encode products that are able to substitute for the product of the mutated gene. Alternatively, the inserts may contain sequences which titrate a repressor protein. In either case, the data suggest that suppression of EMS- and UV-induced mutants occurs when heterologous clones are present in multiple copies.

• Authors: H V Kamdar, K B Rowley, D Clements, S S Patil
• Journal: Journal of bacteriology (J Bacteriol) Vol. 173 Issue 3 Pg. 1073-9 (Feb 1991) ISSN: 0021-9193 [Print] United States
• PMID: 1991709 (Publication Type: Journal Article, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• DNA, Bacterial
• Exotoxins
• phaseolotoxin
• Ethyl Methanesulfonate
• Ornithine

Topics

• Base Sequence
• Blotting, Southern
• Cloning, Molecular
• Cosmids
• DNA, Bacterial (genetics)
• Ethyl Methanesulfonate (pharmacology)
• Exotoxins (biosynthesis, genetics, radiation effects)
• Mutagenesis
• Mutation
• Ornithine (analogs & derivatives)
• Phenotype
• Pseudomonas (genetics)
• Restriction Mapping
• Suppression, Genetic
• Ultraviolet Rays