Role of the OTAbZIP gene in regulating growth and OTA production in Aspergillus westerdijkiae fc-1 under osmotic stress

Ochratoxin A (OTA), a potent carcinogenic mycotoxin, is produced by fungi from the Aspergillus and Penicillium genera. Reducing OTA contamination in food remains a global challenge. Osmotic stress is a key factor that influencing fungal development and secondary metabolism, particularly in Aspergillus species. In this study, we explored regulatory role of the OTAbZIP gene, a bZIP-type transcription factor, in growth and OTA biosynthesis under varying NaCl-induced osmotic conditions. Using RNA-Seq and RT-qPCR, we analyzed the transcriptomic responses of wild-type (WT) and ΔOTAbZIP mutant strains of Aspergillus westerdijkiae fc-1 exposed to 0, 20, and 100 g/L NaCl. Deletion of OTAbZIP significantly altered the expression of genes involved in DNA replication, sugar metabolism, ribosome function, and arginine and proline metabolism. The ΔOTAbZIP mutant exhibited greater sensitivity to osmotic stress and lower expression of OTA biosynthetic genes (otaA–D) than the WT. Although components of the HOG-MAPK pathway (Hog1, Gpd1, Cdc28, and Ctt1) were differentially expressed, OTAbZIP deletion did not block Hog1 activation, suggesting OTAbZIP may function in a distinct regulatory role upstream or parallel to this pathway. Overall, our findings highlight OTAbZIP as a key regulator of osmotic stress response and OTA biosynthesis in A. westerdijkiae, offering potential molecular targets to reduce OTA contamination in food and feed.