Set3 Is Required for Asexual Development, Aflatoxin Biosynthesis, and Fungal Virulence in Aspergillus flavus

Abstract

<i>Aspergillus flavus</i> is an opportunistic pathogenic fungus for both plant and animal that produces carcinogenic toxins termed aflatoxins (AFs). To identify possible genetic targets to reduce AF contamination, in this study, we have characterized a novel <i>A. flavus</i> Set3, and it shares sequence homology with the yeast protein Set3. The <i>set3</i> deletion mutants present no difference in growth rate but alterations in asexual development and secondary metabolite production when compared to the <i>A. flavus</i> wild type. Specifically, deletion of <i>set3</i> gene decreases conidiophore formation and conidial production through downregulating expression of <i>brlA</i> and <i>abaA</i> genes. In addition, normal levels of <i>set3</i> are required for sclerotial development and expression of sclerotia-related genes <i>nsdC</i> and <i>sclR</i>. Further analyses demonstrated that Set3 negatively regulates AF production as well as the concomitant expression of genes in the AF gene cluster. Importantly, our results also display that <i>A. flavus</i> Set3 is involved in crop kernel colonization. Taking together, these results reveal that a novel Set3 plays crucial roles in morphological development, secondary metabolism, and fungal virulence in <i>A. flavus</i>.