title: Identification of pathogenicity-related genes in Fusarium oxysporum f. sp. cepae.
abstract: Pathogenic isolates of Fusarium oxysporum, distinguished as formae speciales (f. spp.) on the basis of their host specificity, cause crown rots, root rots and vascular wilts on many important crops worldwide. Fusarium oxysporum f. sp. cepae (FOC) is particularly problematic to onion growers worldwide and is increasing in prevalence in the UK. We characterized 31 F. oxysporum isolates collected from UK onions using pathogenicity tests, sequencing of housekeeping genes and identification of effectors. In onion seedling and bulb tests, 21 isolates were pathogenic and 10 were non-pathogenic. The molecular characterization of these isolates, and 21 additional isolates comprising other f. spp. and different Fusarium species, was carried out by sequencing three housekeeping genes. A concatenated tree separated the F. oxysporum isolates into six clades, but did not distinguish between pathogenic and non-pathogenic isolates. Ten putative effectors were identified within FOC, including seven Secreted In Xylem (SIX) genes first reported in F. oxysporum f. sp. lycopersici. Two highly homologous proteins with signal peptides and RxLR motifs (CRX1/CRX2) and a gene with no previously characterized domains (C5) were also identified. The presence/absence of nine of these genes was strongly related to pathogenicity against onion and all were shown to be expressed in planta. Different SIX gene complements were identified in other f. spp., but none were identified in three other Fusarium species from onion. Although the FOC SIX genes had a high level of homology with other f. spp., there were clear differences in sequences which were unique to FOC, whereas CRX1 and C5 genes appear to be largely FOC specific.
authors.affiliation: Warwick Crop Centre, School of Life Sciences, University of Warwick, Wellesbourne, Warwick, CV35 9EF, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Taylor
authors.affiliation: Warwick Crop Centre, School of Life Sciences, University of Warwick, Wellesbourne, Warwick, CV35 9EF, UK.
authors.forename: Viktória
authors.initials: V
authors.lastname: Vágány
authors.affiliation: Warwick Crop Centre, School of Life Sciences, University of Warwick, Wellesbourne, Warwick, CV35 9EF, UK.
authors.forename: Alison C
authors.initials: AC
authors.lastname: Jackson
authors.affiliation: East Malling Research, New Road, East Malling, Kent, ME19 6BJ, UK.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Harrison
authors.affiliation: Warwick Crop Centre, School of Life Sciences, University of Warwick, Wellesbourne, Warwick, CV35 9EF, UK.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Rainoni
authors.affiliation: Warwick Crop Centre, School of Life Sciences, University of Warwick, Wellesbourne, Warwick, CV35 9EF, UK.
authors.forename: John P
authors.initials: JP
authors.lastname: Clarkson
mesh_terms: D000595:Amino Acid Sequence; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005670:Fusarium / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity*; D015966:Gene Expression Regulation, Fungal; D018506:Gene Expression Regulation, Plant; D020043:Genes, Essential; D005800:Genes, Fungal; D016013:Likelihood Functions; D019697:Onions / Q000235:genetics / Q000382:microbiology; D010802:Phylogeny; D018517:Plant Roots / Q000235:genetics / Q000382:microbiology; D016415:Sequence Alignment; D013045:Species Specificity
chemical_list: D005656:Fungal Proteins
keywords: Fusarium basal rot; Fusarium oxysporum f. sp. cepae; Secreted In Xylem (SIX); effector genes; onion; pathogenicity