Down-regulation of aflatoxin biosynthetic genes in Aspergillus parasiticus by Heliopsis longipes roots and affinin for reduction of aflatoxin production.

Affinin present in roots has been identified as an anti-aflatoxin molecule. However, its mechanism of action has yet to be clarified. Aflatoxins biosynthesis involves not less than 27 enzymatic reactions. In this work, the genes G, H, I, K, L, M, O, P, and Q of the aflatoxins cluster and the S gene encoding an internal regulatory factor involved in aflatoxins biosynthesis in were studied by qRT-PCR. Results demonstrated that ethanolic extract of roots and affinin inhibit aflatoxin biosynthesis and fungal growth in a dose-dependent manner. At 300 µg/mL, ethanolic extract and affinin presented the highest inhibition of radial growth (86% and 94%) and aflatoxin production (68% and 80%). The qRT-PCR analysis demonstrated that nine tested genes were down-regulated by affinin and ethanolic extract. The most down-regulated was the K, a gene that encodes an enzyme cyclase with double function during the aflatoxin biosynthesis. While no significant down-regulation was obtaining for H gene. Exposure to affinin also resulted in decreased transcript levels of the internal regulator factor S. Based on our results, a model showing the regulatory mechanism in aflatoxin biosynthesis and its role in gene expression was proposed. In conclusion, affinin modulates the expression of several aflatoxin biosynthetic genes, leading to mycotoxin biosynthesis inhibition. Therefore, roots is a suitable candidate to developed control strategies via lowering gene expressions as a future perspective in reducing aflatoxin contamination.