title: Fungal-specific transcription factor AbPf2 activates pathogenicity in Alternaria brassicicola.
abstract: Alternaria brassicicola is a successful saprophyte and necrotrophic plant pathogen. To identify molecular determinants of pathogenicity, we created non-pathogenic mutants of a transcription factor-encoding gene, AbPf2. The frequency and timing of germination and appressorium formation on host plants were similar between the non-pathogenic ∆abpf2 mutants and wild-type A. brassicicola. The mutants were also similar in vitro to wild-type A. brassicicola in terms of vegetative growth, conidium production, and responses to a phytoalexin, reactive oxygen species and osmolites. The hyphae of the mutants grew slowly but did not cause disease symptoms on the surface of host plants. Transcripts of the AbPf2 gene increased exponentially soon after wild-type conidia contacted their host plants . A small amount of AbPf2 protein, as monitored using GFP fusions, was present in young, mature conidia. The protein level decreased during saprophytic growth, but increased and was located primarily in fungal nuclei during pathogenesis. Levels of the proteins and transcripts sharply decreased following colonization of host tissues beyond the initial infection site. When expression of the transcription factor was induced in the wild-type during early pathogenesis, 106 fungal genes were also induced in the wild-type but not in the ∆abpf2 mutants. Notably, 33 of the 106 genes encoded secreted proteins, including eight putative effector proteins. Plants inoculated with ∆abpf2 mutants expressed higher levels of genes associated with photosynthesis, the pentose phosphate pathway and primary metabolism, but lower levels of defense-related genes. Our results suggest that AbPf2 is an important regulator of pathogenesis, but does not affect other cellular processes in A. brassicicola.
authors.affiliation: Plant and Environmental Protection Sciences, University of Hawaii at Manoa, 3190 Maile Way, St John 317, Honolulu, HI 96822, USA. yangrae@hawaii.edu
authors.forename: Yangrae
authors.initials: Y
authors.lastname: Cho
authors.forename: Robin A
authors.initials: RA
authors.lastname: Ohm
authors.forename: Igor V
authors.initials: IV
authors.lastname: Grigoriev
authors.forename: Akhil
authors.initials: A
authors.lastname: Srivastava
mesh_terms: D000528:Alternaria / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*; D017360:Arabidopsis / Q000382:microbiology; D001483:Base Sequence; D001937:Brassica / Q000382:microbiology; D017124:Conserved Sequence; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D054884:Host-Pathogen Interactions / Q000235:genetics; D025301:Hyphae / Q000235:genetics; D009154:Mutation; D010935:Plant Diseases / Q000382:microbiology; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013172:Spores, Fungal / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins
keywords: Alternaria brassicicola; Brassica oleracea; gene expression profile; gene induction; necrotrophic fungus; pathogenesis mechanism; pathogenesis regulator; plant response to pathogen