Seed Lipoxygenase Products Modulate Aspergillus Mycotoxin Biosynthesis

Abstract

Oilseed crops are frequently subject to contamination by mycotoxins produced by Aspergillus spp., particularly aflatoxin (AF) and to a lesser extent sterigmatocystin (ST). Several studies have suggested that metabolites generated from the plant lipoxygenase (LOX) pathway may either decrease or increase mycotoxin production by Aspergillus spp. We tested the possibility that the occurrence of seed LOX isozymes that produce distinct hydroperoxy fatty acids may account for these different effects on AF biosynthesis. For example, soybean LOX1 catalyzes the addition of O2 to the C13 position of linoleic and linolenic acids while maize embryo LOX catalyzes the addition of O2 to the C9 position. In vitro experiments showed that 13S-hydroperoxy fatty acids at concentrations of 10 and 100 μM repressed AF and ST pathway gene expression and significantly (P = 0.05) reduced AF and ST production in both A. parasiticus (AF producer) and A. nidulans (ST producer). Treatment with 1 μM 13S-hydroperoxy linoleic acid also significantly decreased AF production when introduced into growth media at continuous 24-h intervals. In contrast, the same concentrations of 9S-hydroperoxy linoleic acid did not reduce AF or ST production but extended the length of time AF and ST transcripts were detectable. These results show that 13S-hydroperoxy fatty acids directly or indirectly repress AF and ST biosynthesis and provide in vitro evidence that specific seed lipoxygenase activity could provide resistance to mycotoxin contamination by Aspergillus spp.