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ARS Home » Southeast Area » Tifton, Georgia » Crop Protection and Management Research » Research » Publications at this Location » Publication #335108
Title: Responses of Aspergillus flavus to oxidative stress are related to fungal development regulator, antioxidant enzyme, and secondary metabolite biosynthetic gene expression

Author
item FOUNTAIN, JAKE - University Of Georgia
item BAJAJ, PRASAD - International Crops Research Institute For Semi-Arid Tropics (ICRISAT) - India
item NAYAK, SPURTHI - International Crops Research Institute For Semi-Arid Tropics (ICRISAT) - India
item YANG, LIMING - University Of Georgia
item PANDEY, MANISH - International Crops Research Institute For Semi-Arid Tropics (ICRISAT) - India
item KUMAR, VINAY - International Crops Research Institute For Semi-Arid Tropics (ICRISAT) - India
item JAYALE, ASHWIN - International Crops Research Institute For Semi-Arid Tropics (ICRISAT) - India
item CHITIKINENI, ANU - International Crops Research Institute For Semi-Arid Tropics (ICRISAT) - India
item LEE, ROBERT - University Of Georgia
item KEMERAIT, ROBERT - University Of Georgia
item VARSHNEY, RAJEEV - International Crops Research Institute For Semi-Arid Tropics (ICRISAT) - India
item Guo, Baozhu

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2016
Publication Date: 12/21/2016
Citation: Fountain, J.C., Bajaj, P., Nayak, S.N., Yang, L., Pandey, M.K., Kumar, V., Jayale, A.S., Chitikineni, A., Lee, R.D., Kemerait, R.C., Varshney, R.K., Guo, B. 2016. Responses of Aspergillus flavus to oxidative stress are related to fungal development regulator, antioxidant enzyme, and secondary metabolite biosynthetic gene expression. Frontiers in Microbiology. 7:2048 doi: 10.3389/fmicb.2016.02048.

Interpretive Summary: The contamination of crops with aflatoxin is a threat to human health, global food safety and security. In our previous studies, isolates of Aspergillus flavus were found to exhibit different degrees of oxidative stress tolerance which appeared to correlate with their aflatoxin production capability suggesting that aflatoxin production may contribute to stress tolerance. In order to better understand the differences in isolate-specific responses to oxidative stress, and to further explore the potential role of aflatoxin production in stress alleviation in A. flavus, we examined the global transcriptional responses of several isolates of A. flavus to increasing oxidative stress. In this study, we report a detailed analysis of changes in the transcriptomes of different toxigenic A. flavus isolates with distinguished aflatoxin production capabilities to increasing oxidative stress in an aflatoxin conducive culture medium. Isolates which produced higher levels of aflatoxin tended to exhibit fewer differentially expressed genes than isolates with lower levels of production. Genes found to be differentially expressed in response to increasing oxidative stress included antioxidant enzymes, primary metabolism components, antibiosis-related genes, and secondary metabolite biosynthetic components specifically for aflatoxin, aflatrem, and kojic acid. Aflatoxin biosynthetic genes and antioxidant enzyme genes were also found to be co-expressed and highly correlated with fungal biomass under stress. This suggests that these secondary metabolites may be produced as part of coordinated oxidative stress responses in A. flavus along with antioxidant enzyme gene expression and developmental regulation.

Technical Abstract: The infection of maize and peanut with Aspergillus flavus and subsequent contamination with aflatoxin pose a threat to global food safety and human health, and is exacerbated by drought stress. Drought stress-responding compounds such as reactive oxygen species (ROS) are associated with fungal stress responsive signaling and secondary metabolite production, and can stimulate the production of aflatoxin by A. flavus in vitro. These secondary metabolites have been shown to possess diverse functions in soil-borne fungi including antibiosis, competitive inhibition of other microbes, and abiotic stress alleviation. Previously, we observed that isolates of A. flavus showed differences in oxidative stress tolerance which correlated with their aflatoxin production capabilities. In order to better understand these isolate-specific oxidative stress responses, we examined the transcriptional responses of field isolates of A. flavus with varying levels of aflatoxin production (NRRL3357, AF13, and Tox4) to H2O2-induced oxidative stress. Isolates which produced higher levels of aflatoxin tended to exhibit fewer differentially expressed genes than isolates with lower levels of production. Genes found to be differentially expressed in response to increasing oxidative stress included antioxidant enzymes, primary metabolism components, antibiosis-related genes, and secondary metabolite biosynthetic components specifically for aflatoxin, aflatrem, and kojic acid. The expression of fungal development-related genes including aminobenzoate degradation genes and conidiation regulators were found to be regulated in response to increasing stress. Aflatoxin biosynthetic genes and antioxidant enzyme genes were also found to be co-expressed and highly correlated with fungal biomass under stress. This suggests that these secondary metabolites may be produced as part of coordinated oxidative stress responses in A. flavus along with antioxidant enzyme gene expression and developmental regulation.