title: Identification of virulence genes in Fusarium oxysporum f. sp. lycopersici by large-scale transposon tagging.
abstract: Forward genetic screens are efficient tools for the dissection of complex biological processes, such as fungal pathogenicity. A transposon tagging system was developed in the vascular wilt fungus Fusarium oxysporum f. sp. lycopersici by inserting the novel modified impala element imp160::gfp upstream of the Aspergillus nidulans niaD gene, followed by transactivation with a constitutively expressed transposase. A collection of 2072 Nia(+) revertants was obtained from reporter strain T12 and screened for alterations in virulence, using a rapid assay for invasive growth on apple slices. Seven strains exhibited reduced virulence on both apple slices and intact tomato plants. Five of these were true revertants showing the re-insertion of imp160::gfp within or upstream of predicted coding regions, whereas the other two showed either excision without re-insertion or no excision. Linkage between imp160::gfp insertion and virulence phenotype was determined in four transposon-tagged loci using targeted deletion in the wild-type strain. Knockout mutants in one of the genes, FOXG_00016, displayed significantly reduced virulence, and complementation of the original revertant with the wild-type FOXG_00016 allele fully restored virulence. FOXG_00016 has homology to the velvet gene family of A. nidulans. The high rate of untagged virulence mutations in the T12 reporter strain appears to be associated with increased genetic instability, possibly as a result of the transactivation of endogenous transposable elements by the constitutively expressed transposase.
authors.affiliation: Departamento de Genética, Universidad de Córdoba, Campus Universitario de Rabanales, Edif C5, 14071 Córdoba, Spain.
authors.forename: Manuel Sánchez
authors.initials: MS
authors.lastname: López-Berges
authors.forename: Antonio
authors.initials: A
authors.lastname: DI Pietro
authors.forename: Marie-Josée
authors.initials: MJ
authors.lastname: Daboussi
authors.forename: Hala Abdel
authors.initials: HA
authors.lastname: Wahab
authors.forename: Christelle
authors.initials: C
authors.lastname: Vasnier
authors.forename: M Isabel G
authors.initials: MI
authors.lastname: Roncero
authors.forename: Marie
authors.initials: M
authors.lastname: Dufresne
authors.forename: Concepción
authors.initials: C
authors.lastname: Hera
mesh_terms: D001233:Aspergillus nidulans / Q000235:genetics; D004251:DNA Transposable Elements; D005670:Fusarium / Q000235:genetics / Q000472:pathogenicity*; D005800:Genes, Fungal; D049452:Green Fluorescent Proteins / Q000235:genetics; D018551:Solanum lycopersicum / Q000382:microbiology; D016254:Mutagenesis, Insertional; D010957:Plasmids; D016133:Polymerase Chain Reaction; D014774:Virulence / Q000235:genetics*
chemical_list: D004251:DNA Transposable Elements; D049452:Green Fluorescent Proteins