YAP1-LIKE GENE MODULATES AFLATOXIN BIOSYNTHESIS IN ASPERGILLUS PARASITICUS.

In Aspergillus parasiticus Speare, NRRL 2999, lipoperoxide promotes aflatoxin biosynthesis in media favouring and not favouring their biosynthesis (potato dextrose broth -PDB- and czapek dox broth -CD-, respectively). To stimulate oxidative stress in CD, cumene hydroperoxide (CH, 1 mM), a lipoperoxidation inducer, was used. The two regioisomers of the hydroperoxides of linoleic acid (9-HODE and 13-HODE) were analysed in A. parasiticus mycelia by liquid chromatography-mass spectrometry (LC-MS). Some oxidative stress-related transcription factors such as yap1-like, skn7-like and hsf2-like appeared to drive, following their activation, the correlation between oxidative stress in the mycelia and aflatoxin biosynthesis. Expression of these factors led to the activation of defence responses of A. parasiticus cells such as antioxidant enzyme activities: superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX). In accordance with the role played by antioxidant machinery in the cell and toxin biosynthesis, the well-known antioxidants caffeic acid and BHA, were able to inhibit lipoperoxide formation and aflatoxin biosynthesis. The A. parasiticus mutant Δyap1-like grown in an aflatoxin conducive medium (PDB) anticipated and increased aflatoxin biosynthesis in comparison to wild type and, at the same time, markedly inhibited SOD, CAT and GPX activity. Probably in Δyap1-like strain the cell environment is more suitable to support earlier and higher toxin formation. Reactive species as lipoperoxides formed during fungal growth create a stressing environment in front of which fungal cell activates oxidative stress transcription factors and aflatoxin biosynthesis. Yap1-like appears to play a modulating role in metabolic events leading to aflatoxin biosynthesis in A. parasiticus.