Pathogen Genetics and Genomics

The development of expressed sequence tag (EST) databases, directed transformation and a sequenced genome have facilitated the functional analyses of Fusarium graminearum genes. Extensive analysis of 10,397 ESTs, derived from thirteen cDNA libraries of F. graminearum grown under diverse conditions, identified a novel cluster of eight genes (gene loci fg08077 – fg08084) located within a 17 kb region of genomic sequence contig 1.324. The expression of these genes, as detected by Northern analysis and qPCR, is concomitantly up-regulated under growth conditions that promote mycotoxin production. Gene disruption experiments followed by metabolite analysis of the transformants indicated that one of the genes, fg08079, is directly involved in butenolide synthesis, a secondary metabolite derived from glutamic acid. The mycotoxin butenolide is produced by several Fusarium species and has been suggested, but not proven, to be associated with tall fescue toxicoses in grazing cattle. To confirm that this gene is involved in butenolide biosynthesis, the complete, intact gene was added back to the disruption mutants. The add-back transformants were once again able to synthesize butenolide. As expression of these genes can be detected very early in wheat and barley infection, butenolide may play a role in plant infection. However, greenhouse testing for FHB (Fusarium Head Blight) using disruption mutants of fg08079, showed that this gene did not contribute significantly to virulence in wheat heads. We will continue to exploit genomic and proteomic tools to identify genes that are involved in FHB disease.