Role of the OTAbZIP Gene in Regulating Growth and OTA Production in Aspergillus westerdijkiae fc-1 Under Osmotic Stress

Background Ochratoxins are toxins primarily produced by fungi from the Aspergillus and Penicillium genera. Among these, Ochratoxin A (OTA) is the most toxic and exhibits strong carcinogenic effects. Reducing food contamination by OTA is a critical global challenge. Osmotic pressure is an important environmental factor that regulates various metabolic pathways in Aspergillus westerdijkiae . It particularly affects the HOG pathway, which controls fungal mycelium growth and OTA production. The OTAbZIP gene is a key transcription factor and receptor in A. westerdijkiae . It plays a vital role in responding to osmotic pressure and regulating the expression of OTA biosynthesis genes ( otaA-D ). This study explored the role of OTAbZIP in fungal growth and OTA production under different osmotic conditions using RNA-Seq and RT-qPCR analyses. Results Transcriptomic analysis showed that the OTAbZIP gene influences several pathways. These include DNA replication, sugar metabolism, ribosome function, and arginine and proline metabolism at NaCl concentrations of 0, 20, and 100 g/L. Genes in the high osmolarity glycerol, mitogen-activated protein kinase (MAPK HOG) pathway, such as Hog1 , Gpd1 , Cdc28 , and Ctt1 were affected. The ΔOTAbZIP mutant strain exhibited increased sensitivity to osmotic stress. RT-qPCR results confirmed that OTA biosynthesis gene expression was significantly lower in the ΔOTAbZIP mutant strain than in the wild-type (WT) strain of A. westerdijkiae fc-1. However, the ΔOTAbZIP mutation did not affect the activation of the Hog1 gene. Conclusions This study highlights the role of the OTAbZIP gene in regulating metabolic pathways linked to growth and OTA production in A. westerdijkiae fc-1. These findings enhance our understanding of the gene's functions of A. westerdijkiae fc-1 under various somatic pressures. They also offer insights for developing strategies to control OTA contamination in food and feed.