Sfp-type 4'-phosphopantetheinyl transferase is required for lysine synthesis, tolerance to oxidative stress and virulence in the plant pathogenic fungus Cochliobolus sativus.
Polyketide synthases (PKSs) and nonribosomal peptide synthetases (NRPSs) are the major enzymes involved in the biosynthesis of secondary metabolites, which have diverse activities, including roles as pathogenicity/virulence factors in plant pathogenic fungi. These enzymes are activated by 4'-phosphopantetheinylation at the conserved serine residues, which is catalysed by 4'-phosphopantetheinyl transferase (PPTase). PPTase is also required for primary metabolism (α-aminoadipate reductase, AAR). In the genome sequence of the cereal fungal pathogen Cochliobolus sativus, we identified a gene (PPT1) orthologous to the PPTase-encoding genes found in other filamentous ascomycetes. The deletion of PPT1 in C. sativus generated mutants (Δppt1) that were auxotrophic for lysine, unable to synthesize melanin, hypersensitive to oxidative stress and significantly reduced in virulence to barley cv. Bowman. To analyse the pleiotropic effects of PPT1, we also characterized deletion mutants for PKS1 (involved in melanin synthesis), AAR1 (for AAR) and NPS6 (involved in siderophore-mediated iron metabolism). The melanin-deficient strain (Δpks1) showed no differences in pathogenicity and virulence compared with the wild-type strain. Lysine-auxotrophic mutants (Δaar1) induced spot blotch symptoms, as produced by the wild-type strain, when inoculated on wounded barley leaves or when lysine was supplemented. The Δnps6 strain showed a slightly reduced virulence compared with the wild-type strain, but exhibited significantly higher virulence than the Δppt1 strain. Our results suggest that an unknown virulence factor, presumably synthesized by PKSs or NRPSs which are activated by PPTase, is directly responsible for high virulence of C. sativus on barley cv. Bowman.
Department of Plant Pathology, North Dakota State University, Fargo, ND 58108, USA.
Yueqiang
Y
Leng
Shaobin
S
Zhong
D000222:Adaptation, Physiological / Q000187:drug effects; D001203:Ascomycota / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development / Q000472:pathogenicity*; D001426:Bacterial Proteins / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism; D017353:Gene Deletion; D001467:Hordeum / Q000187:drug effects / Q000382:microbiology*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D000090463:Iron Deficiencies; D008239:Lysine / Q000096:biosynthesis*; D008543:Melanins / Q000378:metabolism; D008969:Molecular Sequence Data; D018384:Oxidative Stress / Q000187:drug effects; D010935:Plant Diseases / Q000382:microbiology; D017386:Sequence Homology, Amino Acid; D013172:Spores, Fungal / Q000187:drug effects / Q000254:growth & development; D017855:Transferases (Other Substituted Phosphate Groups) / Q000378:metabolism*; D014774:Virulence / Q000187:drug effects
D001426:Bacterial Proteins; D005656:Fungal Proteins; D008543:Melanins; C082662:phosphopantetheinyl transferase; D006861:Hydrogen Peroxide; D017855:Transferases (Other Substituted Phosphate Groups); D008239:Lysine