Influence of water activity on fumonisin and bikaverin gene expression and toxin production in Fusarium verticillioides

Fusarium verticillioides, the main cause of ear rot disease of maize, can produce a variety of secondary metabolites including fumonisins (FBs) and bikaverin (BIK). The former are toxins known to cause diseases and cancers in both animals and humans; the latter is a red-pigment with self-defence activity for the fungus. Water activity (aw) is one of the main environmental factors known to influence secondary metabolite production in filamentous fungi. The biosynthetic pathways of these metabolites are under study; however the conditions at which genes regulating the pathways are activated are not clearly understood. In this work, we studied the production of FBs and BIK and the expression of 4 FUM genes (FUM3, FUM8, FUM13 and FUM14) and BIK1 in two F. verticillioides strains in relation to changing of aw. FBs and BIK were produced by both strains and FBs level was around 5 times higher than BIK. Both their synthesis was favoured by higher aw=0.990. FUM genes and BIK1 were expressed at all conditions studied. The higher transcription level was observed in strain 1744; FUM14 and BIK1 were respectively the highest and the lowest genes expressed. At lower aw=0.955 the expression of both FUM genes and BIK1 decreased at 21 days, while at aw=0.990 all genes had the opposite behaviour. These results showed a significant influence of aw on F. verticillioides secondary metabolites production and expression of the genes involved and further confirmed the relationship between FUM and BIK genes expression under FBs-inducing conditions.