Identification of ABC Transporter Genes of <i>Fusarium graminearum</i> with Roles in Azole Tolerance and/or Virulence

<div><p><i>Fusarium graminearum</i> is a plant pathogen infecting several important cereals, resulting in substantial yield losses and mycotoxin contamination of the grain. Triazole fungicides are used to control diseases caused by this fungus on a worldwide scale. Our previous microarray study indicated that 15 ABC transporter genes were transcriptionally upregulated in response to tebuconazole treatment. Here, we deleted four ABC transporter genes in two genetic backgrounds of <i>F. graminearum</i> representing the DON (deoxynivalenol) and the NIV (nivalenol) trichothecene chemotypes. Deletion of <i>FgABC3</i> and <i>FgABC4</i> belonging to group I of ABC-G and to group V of ABC-C subfamilies of ABC transporters, respectively, considerably increased the sensitivity to the class I sterol biosynthesis inhibitors triazoles and fenarimol. Such effects were specific since they did not occur with any other fungicide class tested. Assessing the contribution of the four ABC transporters to virulence of <i>F. graminearum</i> revealed that, irrespective of their chemotypes, deletion mutants of <i>FgABC1</i> (ABC-C subfamily group V) and <i>FgABC3</i> were impeded in virulence on wheat, barley and maize. Phylogenetic context and analyses of mycotoxin production suggests that <i>FgABC3</i> may encode a transporter protecting the fungus from host-derived antifungal molecules. In contrast, <i>FgABC1</i> may encode a transporter responsible for the secretion of fungal secondary metabolites alleviating defence of the host. Our results show that ABC transporters play important and diverse roles in both fungicide resistance and pathogenesis of <i>F. graminearum</i>.</p>