Effects of temperature and water activity on FUM2 and FUM21 gene expression and fumonisin B production in Fusarium verticillioides

The fungus Fusarium verticillioides is a pathogen of maize and can produce the mycotoxins fumonisins. The present work examined the effect of abiotic factors on the expression of two fumonisin biosynthetic genes (FUM2 and FUM21) and fumonisin production in the fungus. Specifically, the effects of water activity (0.901-0.990), temperature (20-30°C) and incubation time (7-21 days) were analysed in cultures of F. verticillioides strains ITEM 10027 and ITEM 1744. Fumonisin B were measured through liquid chromatography tandem mass spectrometry and gene expression was quantified with relative real-time PCR, using the Livak method. Fumonisin production increased with incubation time up to 21 days and the transcription of both genes was highest at 14 days; however intraspecific variability was observed. FUM2 and FUM21 expression was positively correlated to fumonisin synthesis (p<=0.01 and 0.05) at different water activity and temperature regimes. . A sensibly higher transcription of FUM2 in comparison with FUM21 was observed for all the conditions considered. Incubation time played a significant role on fumonisin production and gene expression, with the highest contamination and the highest gene expression respectively after 21 and 14 days of incubation. Temperature significantly affected only FUM21 expression, with optimum at 25°C; while water activity did not have a significant effect.