Fusarium graminearum mycotoxins and their biosynthetic genes

The plant pathogenic fungus Fusarium graminearum (teleomorph: Gibberella zeae) is a crucial pathogen of major cereal crops and the fungus has taken on greater importance throughout the world. Taking advantage of rapid progress on fungal molecular techniques, we have studied biosynthetic pathways of harmful secondary metabolites of F. graminearum such as trichothecenes, zearalenone, and aurofusarin. We revealed that both Tri13 and Tri7 genes are requried for the chemotype determination of trichothecenes for nivalenol and 4 -acetyl-nivalenol production, respectively. We also constructed efficient chemotype determination system by utilizing distrupted Tri7 gene sequences of deoxinivalenol producers. Forward and reverse genetic approaches enabled us to characterize the gene clusters responsible for the biosynthesis of two polyketide compounds, zearalenone and aurofusarin. Both gene clusters cover genes encoding polyketide synthases and transcription activators. We also characterized an ABC transporter, ZRA 1, related with zearaleone production and constructed a zearalenone conditional gene expression system from the microarray analyses. These results increased our understanding on Fusarium genetics and mycotoxicology. Our future works will focus on revealing the regulatory mechanisms of toxin production and biological functions of these secondary metabolites.