title: A role for topoisomerase I in Fusarium graminearum and F. culmorum pathogenesis and sporulation.
abstract: Fusarium graminearum and F. culmorum are the causal agents of Fusarium ear blight (FEB) in wheat. A forward genetics approach was taken to discover novel pathogenicity genes in the genome of F. graminearum. A library of transformants created by random plasmid insertional mutagenesis was screened on wheat ears for virulence defects. Plasmid rescue on one of the reduced-virulence mutants revealed a single-copy plasmid insertion in the gene coding for the DNA interacting enzyme, topoisomerase I. Targeted topoisomerase I gene-deletion mutants were created in strains of both F. graminearum and F. culmorum. The top1 mutants of both species exhibited greatly reduced virulence in wheat ear infection assays (GO:0009405 and GO:0044145). Detailed microscopy analyses revealed that top1 hyphal growth was restricted to palea tissue whereas host responses were discernable 1,000 mum further away in the rachis node. Asexual sporulation was reduced in the F. graminearum mutants and was absent from the F. culmorum mutants. The F. graminearum mutant did not develop sexual spores when subjected to an in vitro perithecia production assay. During in vitro growth, the top1 mutants of both species were still able to produce the trichothecene mycotoxin, deoxynivalenol.
authors.affiliation: Centre for Sustainable Pest and Disease Management, Department of Plant Pathology and Microbiology, Rothamsted Research, Hertfordshire, UK.
authors.forename: Thomas K
authors.initials: TK
authors.lastname: Baldwin
authors.forename: Martin
authors.initials: M
authors.lastname: Urban
authors.forename: Neil
authors.initials: N
authors.lastname: Brown
authors.forename: Kim E
authors.initials: KE
authors.lastname: Hammond-Kosack
mesh_terms: D002166:Camptothecin / Q000494:pharmacology; D015169:Colony Count, Microbial; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism*; D005057:Eukaryotic Cells / Q000187:drug effects / Q000201:enzymology; D005670:Fusarium / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development / Q000472:pathogenicity*; D017353:Gene Deletion; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000302:isolation & purification / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D009183:Mycotoxins / Q000096:biosynthesis; D010641:Phenotype; D010802:Phylogeny; D012100:Reproduction, Asexual / Q000187:drug effects; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D013172:Spores, Fungal / Q000187:drug effects / Q000502:physiology*; D014908:Triticum / Q000187:drug effects / Q000382:microbiology
chemical_list: D050505:Mutant Proteins; D009183:Mycotoxins; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin