title: Identification of novel virulence factors associated with signal transduction pathways in Alternaria brassicicola.
abstract: Alternaria brassicicola is an important, necrotrophic fungal pathogen that causes black spot disease on Brassicas. In order to study pathogenicity mechanisms, gene deletion mutants were generated for 21 putative regulatory genes including kinases and transcription factors subjectively selected from the annotated A. brassicicola genome. Except for Ste12, the deletion of the SNF1 kinase, XlnR, and CreA homologues that control cell wall-degrading enzyme production did not significantly affect virulence in contrast to other pathogenic fungi. Only deletion of XlnR but not CreA, Ste12 or SNF1 impaired the fungus' ability to utilize sole carbon sources suggesting Alternaria regulates expression of cell wall-degrading enzymes in a novel manner. In addition, two novel virulence factors encoding a transcription factor (AbPro1) and a two-component histidine kinase gene (AbNIK1) were discovered. Deletion of AbPro1 resulted in a 70% reduction in virulence and a 25% reduction in vegetative growth rates in vitro. Deletion of AbNIK1 resulted in a near complete loss of virulence, increased sensitivity to osmotic stress, and no changes in vegetative growth rates in vitro. Interestingly, addition of long polypeptides to spores of both Deltaabste12 and Deltaabnik1 during inoculations resulted in a complete restoration of pathogenicity through a yet to be defined mechanism.
authors.affiliation: Virginia Bioinformatics Institute and Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
authors.forename: Yangrae
authors.initials: Y
authors.lastname: Cho
authors.forename: Kwang-Hyung
authors.initials: KH
authors.lastname: Kim
authors.forename: Mauricio
authors.initials: M
authors.lastname: La Rota
authors.forename: Derrick
authors.initials: D
authors.lastname: Scott
authors.forename: Graciela
authors.initials: G
authors.lastname: Santopietro
authors.forename: Meagan
authors.initials: M
authors.lastname: Callihan
authors.forename: Thomas K
authors.initials: TK
authors.lastname: Mitchell
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Lawrence
mesh_terms: D000528:Alternaria / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005816:Genetic Complementation Test; D000071677:Histidine Kinase; D016296:Mutagenesis; D010935:Plant Diseases / Q000382:microbiology; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; D014157:Transcription Factors; D037521:Virulence Factors; D011494:Protein Kinases; D000071677:Histidine Kinase