Promoter tools for further development of Aspergillus oryzae as a platform for fungal secondary metabolite production

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>The filamentous fungus<jats:italic>Aspergillus oryzae</jats:italic>is widely used for secondary metabolite production by heterologous expression; thus, a wide variety of promoter tools is necessary to broaden the application of this species. Here we built a procedure to survey<jats:italic>A. flavus</jats:italic>genes constitutively highly expressed in 83 transcriptome datasets obtained under various conditions affecting secondary metabolite production, to find promoters useful for heterologous expression of genes in<jats:italic>A. oryzae</jats:italic>.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>To test the ability of the promoters of the top 6 genes to induce production of a fungal secondary metabolite, ustiloxin B, we inserted the promoters before the start codon of<jats:italic>ustR</jats:italic>, which encodes the transcription factor of the gene cluster responsible for ustiloxin B biosynthesis, in<jats:italic>A. oryzae</jats:italic>. Four of the 6 promoters induced ustiloxin B production in all tested media (solid maize, liquid V8 and PDB media), and also<jats:italic>ustR</jats:italic>expression. Two of the 4 promoters were those of<jats:italic>tef1</jats:italic>and<jats:italic>gpdA</jats:italic>, which are well characterized in<jats:italic>A. oryzae</jats:italic>and<jats:italic>A. nidulans</jats:italic>, respectively, whereas the other two, those of AFLA_030930 and AFLA_113120, are newly reported here and show activities comparable to that of the<jats:italic>gpdA</jats:italic>promoter with respect to induction of gene expression and ustiloxin B production.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>We newly reported two sequences as promoter tools for secondary metabolite production in<jats:italic>A. oryzae</jats:italic>. Our results demonstrate that our simple strategy of surveying for constitutively highly expressed genes in large-scale transcriptome datasets is useful for finding promoter sequences that can be used as heterologous expression tools in<jats:italic>A. oryzae</jats:italic>.</jats:p></jats:sec>