Role of the osaA transcription factor gene in development, secondary metabolism and virulence in Aspergillus flavus

We investigated the role of a putative WOPR transcription factor gene, osaA, in Aspergillus flavus. Deletion of osaA altered key developmental processes, including reduced conidiation and sclerotial formation, and led to decreased production of aflatoxin B1 and cyclopiazonic acid. Interestingly, transcriptome analysis revealed upregulation of aflatoxin biosynthetic genes despite reduced toxin accumulation, suggesting regulation beyond transcription, potentially through cofactors or post-transcriptional mechanisms. The osaA mutant also showed increased expression of genes in the imizoquin and aspirochlorine clusters, reduced fungal burden and aflatoxin content during corn kernel colonization, and changes in cell-wall chitin levels and oxidative stress sensitivity. Promoter analysis of osaA-dependent genes indicated enrichment of motifs associated with stress-responsive regulators such as Sko1 and Cst6. These findings highlight osaA as a central regulator of development, secondary metabolism, and pathogenicity in A. flavus, providing insight into fungal biology and potential strategies for mitigating aflatoxin contamination.