Cholera toxin elevates pathogen resistance and induces pathogenesis-related gene expression in tobacco

EMBO J. 1995 Dec 1;14(23):5753-61.

Abstract

In animals, plants and fungi, cholera toxin (CTX) can activate signalling pathways dependent on heterotrimeric GTP binding proteins (G-proteins). We transformed tobacco plants with a chimeric gene encoding the A1 subunit of CTX regulated by a light-inducible wheat Cab-1 promoter. Tissues of transgenic plants expressing CTX showed greatly reduced susceptibility to the bacterial pathogen Pseudomonas tabaci, accumulated high levels of salicylic acid (SA) and constitutively expressed pathogenesis-related (PR) protein genes encoding PR-1 and the class II isoforms of PR-2 and PR-3. In contrast, the class I isoforms of PR-2 and PR-3 known to be induced in tobacco by stress, by ethylene treatment and as part of the hypersensitive response to infection, were not induced and displayed normal regulation. In good agreement with these results, microinjection experiments demonstrated that CTX or GTP-gamma-S induced the expression of a PR1-GUS reporter gene but not that of a GLB-GUS reporter gene containing the promoter region of a gene encoding the class I isoform of PR-2. Microinjection and grafting experiments strongly suggest that CTX-sensitive G-proteins are important in inducing the expression of a subset of PR genes and that these G-proteins act locally rather than systemically upstream of SA induction.

MeSH terms

  • Cholera Toxin / biosynthesis
  • Cholera Toxin / genetics*
  • GTP-Binding Proteins / physiology
  • Gene Expression Regulation, Plant / genetics
  • Genes, Reporter / genetics
  • Guanosine Triphosphate / pharmacology
  • Immunoblotting
  • Light-Harvesting Protein Complexes*
  • Microinjections
  • Phenotype
  • Photosynthetic Reaction Center Complex Proteins / genetics
  • Plant Proteins / biosynthesis*
  • Plant Proteins / genetics
  • Plants, Genetically Modified / genetics
  • Plants, Toxic*
  • Promoter Regions, Genetic / genetics
  • Pseudomonas / pathogenicity*
  • Salicylates / metabolism
  • Salicylic Acid
  • Signal Transduction
  • Tobacco / genetics*
  • Tobacco / metabolism
  • Tobacco / microbiology
  • Transcription, Genetic / genetics
  • Transformation, Genetic / genetics

Substances

  • Light-Harvesting Protein Complexes
  • Photosynthetic Reaction Center Complex Proteins
  • Plant Proteins
  • Salicylates
  • pathogenesis-related proteins, plant
  • Guanosine Triphosphate
  • Cholera Toxin
  • GTP-Binding Proteins
  • Salicylic Acid