|Kistler, H - Corby|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2005
Publication Date: 7/1/2005
Citation: Seong, K., Hou, Z., Tracy, M., Kistler, H.C., Xu, J. 2005. Random insertional mutagenesis identifies genes associated with virulence in the wheat scab fungus Fusarium graminearum. Phytopathology. 95:744-750. Interpretive Summary: Fusarium head blight is a major threat to the profitable and dependable production of wheat and barley crops in the United States. By understanding the fundamental mechanisms by which these microorganisms cause disease, we may be able to develop novel, stable, and environmentally sensible disease management practices aimed at interfering with the essential processes of pathogenesis. This paper describes several novel mechanisms by which the fungus may cause disease that could be targeted for disease control. These disease management strategies may involve chemical disruption of these vital and newly discovered developmental pathways. The primary users of the research in this publication will be other scientists engaged in research to improve disease management on small grain crops.
Technical Abstract: Fusarium graminearum is an important pathogen of small grains and maize in many areas of the world. Wheat scab (head blight), caused primarily by F. graminearum in North America, poses a major threat to wheat production. To better understand the molecular mechanisms of plant infection and virulence of F. graminearum, we used the REMI (Restriction-Enzyme Mediated Integration) approach to generate random insertional mutants. Eleven pathogenicity mutants were identified by screening 6,500 hygromycin-resistant transformants with a corn silk infection assay and confirmed by wheat head infection assays. Genetic analyses indicated that the defects in plant infection were tagged by the transforming vector in seven of these mutants. In mutant M8, the transforming plasmid was integrated 110-bp upstream from the start codon of the cystathionine beta-lyase gene (CBL1). Gene replacement mutants deleted for CBL1 and the methionine synthase gene MSY1 were also obtained. Both the cbl1 and msy1 deletion mutants were methionine autotrophic and significantly reduced in virulence on corn silks and wheat heads, indicating that the methionine synthesis pathway is important for pathogenesis in F. graminearum. We also have identified genes disrupted by the transforming DNA in five other REMI mutants. In mutants 222 and M68, the transforming vectors were inserted in two housekeeping genes encoding the HMG-CoA reductase and the NADH: ubiquinone oxidoreductase. However, the putative b-ZIP transcription factor gene ZIF1, the transducin beta-subunit-like gene TBL1, and a putative hydrolase gene HYD1 disrupted in mutants M7, M75, and 25C3, respectively, had no known homologs in other filamentous fungi and were likely to be novel fungal virulence factors. The HYD1 gene may be unique for plant pathogens because it has no homolog in Neurospora crassa and Aspergillus nidulans, but it has two homologs in Magnaporthe grisea.