The ochratoxin A (OTA) biosynthetic gene cluster includes a bZIP transcription factor (TF) gene (OTAbzip) that has been identified in different fungal species. However, most previous studies identified the OTAbzip gene in ochratoxigenic fungi using bioinformatics methods, while few studies focused on deleting the gene, let alone overexpressing it, to characterize the function of the OTAbZIP TF. Here, we characterized the AnOTAbZIP TF in an ochratoxigenic isolate of Aspergillus niger by deleting and overexpressing the AnOTAbzip gene and examining the role of AnOTAbZIP in morphological development, OTA biosynthesis, and pathogenicity. Chemical and gene expression analyses revealed that AnOTAbZIP positively regulates OTA biosynthesis, since the loss of OTA production and the downregulation of the OTA biosynthetic genes were observed in the ΔAnOTAbzip strain, compared with the wild-type (WT) and OE::AnOTAbzip strains. In terms of pathogenicity, the ΔAnOTAbzip strain produced a greater lesion on grape berries, especially with respect to the OE::AnOTAbzip strain, rather than WT. Finally, the ΔAnOTAbzip strain was also more tolerant to oxidative stress with respect to the OE::AnOTAbzip and WT strains in that order. These new findings improve our understanding of the AnOTAbZIP regulatory mechanism and help develop strategies to attenuate plant pathogenicity and reduce OTA biosynthesis of A. niger.
Keywords: Aspergillus niger; bZIP transcription factor; fungal growth; gene expression; gene knockout; ochratoxin A; regulation.