Linolenic Acid-Derived Oxylipins Inhibit Aflatoxin Biosynthesis in Aspergillus flavus through Activation of Imizoquin Biosynthesis

Oxylipins play important
signaling roles in aflatoxin
(AF) biosynthesis
in Aspergillus flavus. We previously
showed that exogenous supply of autoxidated linolenic acid (AL) inhibited
AF biosynthesis in A. flavus via oxylipins,
but the molecular mechanism is still unknown. Here, we performed multiomics
analyses of A. flavus grown in media
with or without AL. Targeted metabolite analyses and quantitative
reverse transcription (qRT)-polymerase chain reaction (PCR) showed
that the imizoquin (IMQ) biosynthetic pathway was distinctly upregulated
in the presence of AL. 13C-glucose labeling confirmed in
parallel that the tricarboxylic acid cycle was also enhanced by AL,
consistent with observed increases in mycelial growth. Moreover, we
integrated thermal proteome profiling and molecular dynamics simulations
to identify a potential receptor of AL; AL was found to interact with
a transporter (ImqJ) located in the IMQ gene cluster, primarily through
hydrophobic interactions. Further analyses of strains with an IMQ
pathway transcription factor overexpressed or knocked out confirmed
that this pathway was critical for AL-mediated inhibition of AF biosynthesis.
Comparison of 22 assembled A. flavus and Aspergillus oryzae genomes showed
that genes involved in the IMQ pathway were positively selected in A. oryzae. Taken together, the results of our study
provide novel insights into oxylipin-mediated regulation of AF biosynthesis
and suggest potential methods for preventing AF contamination of crops.