Overexpression of the RNA-binding protein NrdA affects global gene expression and secondary metabolism in Aspergillus species

Abstract

RNA-binding protein Nrd1 plays a role in RNA polymerase II transcription termination. In this study, we showed that the orthologous NrdA is important in global mRNA expression and secondary metabolism in Aspergillus species. We constructed an nrdA conditional expression strain using the Tet-On system in Aspergillus luchuenesis mut. kawachii. Downregulation of nrdA caused a severe growth defect, indicating that NrdA is essential for the proliferation of A. kawachii. Parallel RNA-sequencing and RNA immunoprecipitation-sequencing analysis identified potential NrdA-interacting transcripts, corresponding to 32% of the predicted protein coding genes of A. kawachii. Subsequent gene ontology analysis suggested that overexpression of NrdA affects the production of secondary metabolites. To clarify this, we constructed NrdA-overexpressing strains of Aspergillus nidulans, Aspergillus fumigatus, and Aspergillus oryzae. Overexpression of NrdA reduced the production of sterigmatocystin and penicillin in A. nidulans, as well as that of helvolic acid and pyripyropene A in A. fumigatus. Moreover, it increased the production of kojic acid and reduced production of penicillin in A. oryzae. These effects were accompanied by almost consistent transcriptional changes in the relevant genes. Collectively, these results suggest that NrdA is the essential RNA-binding protein, which plays a significant role in global gene expression and secondary metabolism in Aspergillus species. IMPORTANCE Nrd1, a component of the Nrd1–Nab3–Sen1 complex, is an essential RNA-binding protein involved in transcriptional termination in yeast. However, its role in filamentous fungi has not been studied. In this study, we characterized an orthologous NrdA in the Aspergillus species, identified potential NrdA-interacting mRNA, and investigated the effect of overexpression of NrdA on mRNA expression in Aspergillus luchuensis mut. kawachii. The results indicated that NrdA controls global gene expression involved in versatile metabolic pathways, including the secondary metabolic process. We demonstrated that NrdA overexpression significantly affected the production of secondary metabolites in Aspergillus nidulans, Aspergillus oryzae, and Aspergillus fumigatus. Our findings are of importance to the fungal research community because the secondary metabolism is an industrially and clinically important aspect for the Aspergillus species.