Identification of tomato leaf factors that activate toxin gene expression in Pseudomonas syringae pv. tomato DC3000

• Published in: Phytopathology 1998-10, Vol.88 (10), p.1094-1100
• Main Authors: Li, X.Z. (Agriculture and Agri-Food Canada, London, Ontario, Canada.), Starratt, A.N, Cuppels, D.A
• Format: Article
• Language: English
• Subjects: ACIDE ORGANIQUE; ACIDE PHENOLIQUE; ACIDOS FENOLICOS; ACIDOS ORGANICOS; Bacterial plant pathogens; Biological and medical sciences; CHEMICAL COMPOSITION; CODE GENETIQUE; CODIGO GENETICO; COMPOSICION QUIMICA; COMPOSITION CHIMIQUE; CORONATINE; DANOS POR LA HELADA; DEGAT DU AU GEL; DOSAGE EFFECTS; EFECTOS DE DOSIFICACION; EFFET DOSE; EXPRESION GENICA; EXPRESSION DES GENES; FEUILLE; FITOTOXINAS; FROST DAMAGE; Fundamental and applied biological sciences. Psychology; GENE; GENE EXPRESSION; GENES; GENETIC CODE; HOJAS; ICE NUCLEATION; INAZ GENES; INDUCTION; LEAVES; LYCOPERSICON ESCULENTUM; ORGANIC ACIDS; PATHOGENICITY; Pathology. Damages, economic importance; PATOGENICIDAD; PHENOLIC ACIDS; Phytopathology. Animal pests. Plant and forest protection; PHYTOTOXINE; PHYTOTOXINS; POUVOIR PATHOGENE; PSEUDOMONAS SYRINGAE; QUINIC ACID; REPORTER GENES; SHIKIMIC ACID; TRANSCRIPCION; TRANSCRIPTION
• ISSN: 0031-949X; 1943-7684
• DOI: 10.1094/PHYTO.1998.88.10.1094

Coronatine is a non-host-specific chlorosis-inducing phytotoxin produced by the tomato and crucifer pathogen Pseudomonas syringae pv. tomato DC3000. How the chromosomal gene cluster controlling toxin synthesis in this strain is regulated in planta is unknown. Ice nucleation-active cor:inaZ marker-exchange derivatives of strain DC3000 were used to determine coronatine gene expression in various host and nonhost plants and in a minimal medium supplemented with selected tomato plant constituents. Ice nucleation activity, which was first detected 4 h after inoculation, was highest in cabbage, tomato, and soybean and lowest in melon and cucumber. No correlation existed between bacterial population size and expression level on the various plants. Crude tomato leaf extract and intercellular fluid were strong inducers of toxin synthesis. Based on high-performance liquid chromatography analyses and bioassays, we concluded that the active components of both preparations were malic and citric acids, with minor contributions coming from shikimic and quinic acid. Although several compounds including glucose and inositol activated the toxin genes when tested at high concentrations (3 to 5 mM), shikimic and quinic acids were the only ones with activity at concentrations below 0.1 mM. Neither acid could be used as a sole carbon source by strain DC3000. The signal activity of shikimic acid was enhanced 10-fold by the addition of glucose. None of the plant phenolics that we screened affected coronatine gene expression