Pseudomonas syringaePhytotoxins: Mode of Action, Regulation, and Biosynthesis by Peptide and Polyketide Synthetases

Abstract

SUMMARY Coronatine, syringomycin, syringopeptin, tabtoxin, and phaseolotoxin are the most intensively studied phytotoxins of Pseudomonas syringae, and each contributes significantly to bacterial virulence in plants. Coronatine functions partly as a mimic of methyl jasmonate, a hormone synthesized by plants undergoing biological stress. Syringomycin and syringopeptin form pores in plasma membranes, a process that leads to electrolyte leakage. Tabtoxin and phaseolotoxin are strongly antimicrobial and function by inhibiting glutamine synthetase and ornithine carbamoyltransferase, respectively. Genetic analysis has revealed the mechanisms responsible for toxin biosynthesis. Coronatine biosynthesis requires the cooperation of polyketide and peptide synthetases for the assembly of the coronafacic and coronamic acid moieties, respectively. Tabtoxin is derived from the lysine biosynthetic pathway, whereas syringomycin, syringopeptin, and phaseolotoxin biosynthesis requires peptide synthetases. Activation of phytotoxin synthesis is controlled by diverse environmental factors including plant signal molecules and temperature. Genes involved in the regulation of phytotoxin synthesis have been located within the coronatine and syringomycin gene clusters; however, additional regulatory genes are required for the synthesis of these and other phytotoxins. Global regulatory genes such as gacS modulate phytotoxin production in certain pathovars, indicating the complexity of the regulatory circuits controlling phytotoxin synthesis. The coronatine and syringomycin gene clusters have been intensively characterized and show potential for constructing modified polyketides and peptides. Genetic reprogramming of peptide and polyketide synthetases has been successful, and portions of the coronatine and syringomycin gene clusters could be valuable resources in developing new antimicrobial agents.

The phytopathogenic nature of Dickeya aquatica 174/2 and the dynamic early evolution of Dickeya pathogenicity

“…S3). In addition, genes involved in coronafic acid biosynthesis, a phytotoxin classically produced by Pseudomonas syringae (Bender et al, 1999), were present only in D. gs. poaceaephila and D. dadantii subspecies dieffenbachiae (Supporting Information Table S4), suggesting specific acquisition via HGT.…”

Complete genome sequence and comparative analysis of the metabolically versatile Pseudomonas putida KT2440

“…Comparison of the KT2440 genome with those of the phytopathogens Pseudomonas syringae, Ralstonia solanacearum, Xanthomonas campestris and Xylella fastidiosa reveals that KT2440 lacks the genes of practically all known plant-related virulence traits, such as type III secretion systems and corresponding secreted substrates (Fouts et al, 2002;Guttman et al, 2002;Salanoubat et al, 2002), as well as plant cell wall-degrading enzymes (Cao et al, 2001). The KT2440 genome does contain two operons (PP3790-PP3781 and PP2788-PP2777) related to those for the biosynthesis of secondary metabolites, such as phytotoxin peptides and antibiotics respectively (Bender et al, 1999).…”

The genome of Erwinia tasmaniensis strain Et1/99, a non‐pathogenic bacterium in the genus Erwinia

“…The production of toxins promoting necrosis is widely distributed in plant pathogens. Prominent examples are the non-ribosomal peptides like syringomycin and the type I polyketide coronatine from P. syringae (Bender et al, 1999). However, no hints were found that strain Et1/99 produces such components.…”