RNAseq analysis reveals oxidative stress responses of Aspergillus flavus related to stress tolerance and aflatoxin production

Aflatoxin contamination by Aspergillus flavus is exacerbated by drought stress in the field. Given that reactive oxygen species (ROS) both accumulate in plant tissues during drought and can stimulate aflatoxin production in vitro, we examined the responses of toxigenic isolates of A. flavus to oxidative stress focusing on secondary metabolite production using whole transcriptome sequencing. We examined two high toxin producing isolates, Tox4 and AF13, and one moderate producer, NRRL3357, in aflatoxin conducive yeast extract sucrose medium amended with various levels of H2O2. The high producers exhibited fewer differentially expressed genes (DEGs) than the moderate producer in response to increasing stress. Altered aminobenzoate degradation expression along with altered conidiation and growth also suggests reduced developmental rates in the isolates caused by oxidative stress. Aflatoxin genes were upregulated in response to increasing stress along with genes encoding aflatrem and kojic acid biosynthesis. Additional changes in primary metabolic genes also indicates adaptations to increasing stress. Given that the number and diversity of DEGs observed correlated with previously observed aflatoxin production and oxidative stress tolerance for each isolate, these data suggest that secondary metabolite production is involved in A. flavus oxidative responses. Continuing proteomic analyses using gel and iTRAQ methods are underway to confirm the transcriptome results