Integrated Transcriptome and Proteome Analyses Reveal a Close Association Between Secondary Metabolite Production Capabilities and Aspergillus flavus Isolate Oxidative Stress Tolerance

The contamination of crops with aflatoxins during Aspergillus flavus infection is exacerbated by drought stress. Reactive oxygen species have been shown to be produced in plant tissues in response to drought and to stimulate the production of aflatoxin by A. flavus in vitro. To better understand the role of aflatoxin production in oxidative stress responses and contributing factors of isolate-to-isolate variation in stress tolerance, transcriptomes and proteomes of select toxigenic and atoxigenic isolates of A. flavus were examined in medium supplemented with varying levels of H₂O₂. Isolates with greater oxidative stress tolerance and aflatoxin production capability exhibited fewer differentially expressed genes (DEGs) and proteins (DEPs). Comparative analyses between the proteome and transcriptome data showed a weak correlation between significant DEGs and protein fold changes (r = 0.2477) and between DEPs and transcript fold changes (r = 0.1114). Several metabolic pathways were commonly regulated in both datasets including carbon metabolism, aminobenzoate degradation, glutathione metabolism, and secondary metabolite biosynthesis. Aflatoxin and aflatrem biosynthetic components were found to be significantly regulated in both studies in response to increasing stress. Kojic acid biosynthetic genes were also regulated by stress in both toxigenic and atoxigenic isolates. Aflatoxin biosynthetic gene expression was also found to be highly correlated with isolate stress tolerance which implies that this process along with antioxidant benefits afforded by kojic acid and other secondary metabolites may provide partial alleviation of oxidative stress. These additional secondary metabolites may, therefore, be useful in the selection of biological control isolates prior to deployment.