Open AccessIdentification and Characterization of a Well-Defined Series of Coronatine Biosynthetic Mutants of Pseudomonas syringae pv. tomato DC3000
Author(s) -
David Brooks,
Gustavo Hernández-Guzmán,
Andrew P. Kloek,
Francisco J. Alarcón-Chaidez,
Aswathy Sreedharan,
Vidhya Rangaswamy,
Alejandro PeñalozaVázquez,
Carol L. Bender,
Barbara N. Kunkel
Publication year - 2004
Publication title -
molecular plant-microbe interactions
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.565
H-Index - 153
eISSN - 1943-7706
pISSN - 0894-0282
DOI - 10.1094/mpmi.2004.17.2.162
Subject(s) - pseudomonas syringae , coronatine , virulence , mutant , phytotoxin , biology , arabidopsis thaliana , genetics , gene , arabidopsis , microbiology and biotechnology , toxin
To identify Pseudomonas syringae pv. tomato genes involved in pathogenesis, we carried out a screen for Tn5 mutants of P. syringae pv. tomato DC3000 with reduced virulence on Arabidopsis thaliana. Several mutants defining both known and novel virulence loci were identified. Six mutants contained insertions in biosynthetic genes for the phytotoxin coronatine (COR). The P. syringae pv. tomato DC3000 COR genes are chromosomally encoded and are arranged in two separate clusters, which encode enzymes responsible for the synthesis of coronafacic acid (CFA) or coronamic acid (CMA), the two defined intermediates in COR biosynthesis. High-performance liquid chromatography fractionation and exogenous feeding studies confirmed that Tn5 insertions in the cfa and cma genes disrupt CFA and CMA biosynthesis, respectively. All six COR biosynthetic mutants were significantly impaired in their ability to multiply to high levels and to elicit disease symptoms on A. thaliana plants. To assess the relative contributions of CFA, CMA, and COR in virulence, we constructed and characterized cfa6 cmaA double mutant strains. These exhibited virulence phenotypes on A. thalliana identical to those observed for the cmaA or cfa6 single mutants, suggesting that reduced virulence of these mutants on A. thaliana is caused by the absence of the intact COR toxin. This is the first study to use biochemically and genetically defined COR mutants to address the role of COR in pathogenesis.