An oxidoreductase is involved in cercosporin degradation by the bacterium Xanthomonas campestris pv. zinniae

Department of Plant Pathology, 2214 Gardner Hall, North Carolina State University, Raleigh, NC 27695, USA.
Applied and Environmental Microbiology (Impact Factor: 3.67). 10/2006; 72(9):6070-8. DOI: 10.1128/AEM.00483-06
Source: PubMed

ABSTRACT The polyketide toxin cercosporin plays a key role in pathogenesis by fungal species of the genus Cercospora. The bacterium Xanthomonas campestris pv. zinniae is able to rapidly degrade this toxin. Growth of X. campestris pv. zinniae strains in cercosporin-containing medium leads to the breakdown of cercosporin and to the formation of xanosporic acid, a nontoxic breakdown product. Five non-cercosporin-degrading mutants of a strain that rapidly degrades cercosporin (XCZ-3) were generated by ethyl methanesulfonate mutagenesis and were then transformed with a genomic library from the wild-type strain. All five mutants were complemented with the same genomic clone, which encoded a putative transcriptional regulator and an oxidoreductase. Simultaneous expression of these two genes was necessary to complement the mutant phenotype. Sequence analysis of the mutants showed that all five mutants had point mutations in the oxidoreductase gene and no mutations in the regulator. Quantitative reverse transcription-PCR (RT-PCR) showed that the expression of both of these genes in the wild-type strain is upregulated after exposure to cercosporin. Both the oxidoreductase and transcriptional regulator genes were transformed into three non-cercosporin-degrading bacteria to determine if they are sufficient for cercosporin degradation. Quantitative RT-PCR analysis confirmed that the oxidoreductase was expressed in all transconjugants. However, none of the transconjugants were able to degrade cercosporin, suggesting that additional factors are required for cercosporin degradation. Further study of cercosporin degradation in X. campestris pv. zinniae may allow for the engineering of Cercospora-resistant plants by using a suite of genes.

10 Reads
    • "zinniae oxidoreductase (accession no. AAY86766) which has recently been shown to be involved in cercosporin degradation (Taylor et al., 2006). We propose that the function of CTB7 in the cercosporin biosynthetic pathway is probably to catalyse a hydration or reduction step during ring closure to form the polyketomethylene skeleton of cercosporin prior to the methylation steps. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Cercosporin is a non-host-selective, photoactivated polyketide toxin produced by many phytopathogenic Cercospora species, which plays a crucial role during pathogenesis on host plants. Upon illumination, cercosporin converts oxygen molecules to toxic superoxide and singlet oxygen that damage various cellular components and induce lipid peroxidation and electrolyte leakage. Three genes (CTB5, CTB6 and CTB7) encoding putative FAD/FMN- or NADPH-dependent oxidoreductases in the cercosporin toxin biosynthetic pathway of C. nicotianae were functionally analysed. Replacement of each gene via double recombination was utilized to create null mutant strains that were completely impaired in cercosporin production as a consequence of specific interruption at the CTB5, CTB6 or CTB7 locus. Expression of CTB1, CTB5, CTB6, CTB7 and CTB8 was drastically reduced or nearly abolished when CTB5, CTB6 or CTB7 was disrupted. Production of cercosporin was revived when a functional gene cassette was introduced into the respective mutants. All ctb5, ctb6 and ctb7 null mutants retained wild-type levels of resistance against toxicity of cercosporin or singlet-oxygen-generating compounds, indicating that none of the genes plays a role in self-protection.
    Microbiology 09/2007; 153(Pt 8):2781-90. DOI:10.1099/mic.0.2007/007294-0 · 2.56 Impact Factor
  • 01/2007; DOI:10.1094/APSnetFeature/2007-0207
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Not Available
    Vehicular Technology Conference, 2005. VTC-2005-Fall. 2005 IEEE 62nd; 10/2005
Show more


10 Reads
Available from