Transformation of major peanut (arachis hypogaea) stilbenoid phytoalexins caused by selected microorganisms

Authors: Sobolev, Victor; Walk, Travis; Arias De Ares, Renee; Massa, Alicia; Orner, Valerie; Lamb, Marshall

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2022
Publication Date: 1/21/2022
Citation: Sobolev, V., Walk, T., Arias De Ares, R.S., Massa, A.N., Orner, V.A., Lamb, M.C. 2022. Transformation of major peanut (arachis hypogaea) stilbenoid phytoalexins caused by selected microorganisms. Journal of Agricultural and Food Chemistry. 70,1101-1110. https://doi.org/10.1021/acs.jafc.1c06122.
DOI: https://doi.org/10.1021/acs.jafc.1c06122

Interpretive Summary: Common soil fungi, Aspergillus flavus and Aspergillus parasiticus, are opportunistic pathogens that invade preharvest peanut seeds. These fungi often produce carcinogenic aflatoxins that pose a threat to human and animal health through food chains and cause significant economic losses worldwide. The peanut plant accumulates defensive compounds, phytoalexins, in response to the presence of soil fungi, which in turn produce phytoalexin-detoxifying enzymes for successfully invading the plant host. However, the mechanism of peanut-fungus interaction has not been sufficiently studied. We used pure peanut stilbenoids to study their effects on the viability of and metabolite production by several important toxigenic Aspergillus species in comparison with some other fungal and bacterial species. Despite considerable progress in peanut research, relatively little is known about the dynamics of peanut phytoalexin transformation/detoxification by important fungal species. The present research revealed that in feeding experiments, Aspergillus species that commonly infect peanut seeds were capable of degrading the major peanut phytoalexin, arachidin-3, into its hydroxylated homologue and a less toxic pigmented metabolite, SB-1. However, other fungal and bacterial species tested that are not known to be involved in the infection of the peanut plant, were incapable of changing the structure of arachidin-3. The results of feeding experiments with arachidin-1 and resveratrol are also reported. The research provided new knowledge on the dynamics of peanut stilbenoid transformations by essential fungi. These findings may contribute to the elucidation of the phytoalexin detoxification mechanisms involved in the infection of peanut by important toxigenic Aspergillus spp.

Technical Abstract: The peanut plant accumulates defensive stilbenoid phytoalexins in response to the presence of soil fungi, which in turn produce phytoalexin-detoxifying enzymes for successfully invading the plant host. Aspergillus spp. are opportunistic pathogens that invade peanut seeds; most common fungal species often produce highly carcinogenic aflatoxins. The purpose of the present research was to evaluate the in vitro dynamics of peanut phytoalexin transformation/detoxification by important fungal species. The present research revealed that in feeding experiments, Aspergillus spp. from section Flavi were capable of degrading the major peanut phytoalexin, arachidin-3, into its hydroxylated homologue, arachidin-1 and a benzenoid, SB-1. However, A. niger from section Nigri as well as other fungal and bacterial species tested that are not known to be involved in the infection of the peanut plant, were incapable of changing the structure of arachidin-3. The results of feeding experiments with arachidin-1 and resveratrol are also reported. The research provided new knowledge on the dynamics of peanut stilbenoid transformations by essential fungi. These findings may contribute to the elucidation of the phytoalexin detoxification mechanisms involved in the infection of peanut by important toxigenic Aspergillus spp.