Overexpression of the RNA-binding protein NrdA affects global gene expression and secondary metabolism inAspergillusspecies

Abstract

ABSTRACTRNA-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 inAspergillusspecies. We constructed annrdAconditional expression strain using the Tet-On system inAspergillus luchuenesismut.kawachii. Downregulation ofnrdAcaused a severe growth defect, indicating that NrdA is essential for the proliferation ofA. kawachii. Parallel RNA-sequencing and RNA immunoprecipitation-sequencing analysis identified potential NrdA-interacting transcripts, corresponding to 32% of the predicted protein coding genes ofA. kawachii. Subsequent gene ontology analysis suggested that overexpression of NrdA affects the production of secondary metabolites. To clarify this, we constructed NrdA-overexpressing strains ofAspergillus nidulans,Aspergillus fumigatus, andAspergillus oryzae. Overexpression of NrdA reduced the production of sterigmatocystin and penicillin inA. nidulans, as well as that of helvolic acid and pyripyropene A inA. fumigatus. Moreover, it increased the production of kojic acid and reduced production of penicillin inA. 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 inAspergillusspecies.IMPORTANCENrd1, 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 theAspergillusspecies, identified potential NrdA-interacting mRNA, and investigated the effect of overexpression of NrdA on mRNA expression inAspergillus luchuensismut.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 inAspergillus nidulans,Aspergillus oryzae, andAspergillus fumigatus. Our findings are of importance to the fungal research community because the secondary metabolism is an industrially and clinically important aspect for theAspergillusspecies.