SEED LIPOXYGENASE PRODUCTS MODULATE ASPERGILLUS MYCOTOXIN BIOSYNTHESIS

Oilseed crops are frequently subject to contamination by mycotoxins pr oduced by Aspergillus spp., particularly aflatoxin (AF) and to a lesse r extent sterigmatocystin (ST). Several studies have suggested that me tabolites generated from the plant lipoxygenase (LOX) pathway may eith er decrease or increase mycotoxin production by Aspergillus spp. We te sted the possibility that the occurrence of seed LOX isozymes that pro duce distinct hydroperoxy fatty acids may account for these different effects on AF biosynthesis, For example, soybean LOX1 catalyzes the ad dition of O-2 to the C13 position of linoleic and linolenic acids whil e maize embryo LOX catalyzes the addition of O-2 to the C9 position. I n vitro experiments showed that 13S-hydroperoxy fatty acids at concent rations of 10 and 100 mu M 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 wit h 1 mu M 13S-hydroperoxy linoleic acid also significantly decreased AF production when introduced into growth media at continuous 24-h inter vals. In contrast, the same concentrations of 9S-hydroperoxy linoleic acid did not reduce AF or ST production but extended the length of tim e AF and ST transcripts were detectable. These results show that 13S-h ydroperoxy fatty acids directly or indirectly repress AF and ST biosyn thesis and provide in vitro evidence that specific seed lipoxygenase a ctivity could provide resistance to mycotoxin contamination by Aspergi llus spp.