In vitro study of fum gene expression and fumonisins production in Fusarium verticillioides under different ecological conditions.

F. verticillioides is a fungus associated to maize ears all over the world. It can cause Fusarium pink ear rot and produces fumonisins (FBs), mycotoxins found in both maize kernels and its derivatives. They are toxic to humans, in particular FB1 is classified as possibly carcinogenic. Fumonisins biosynthetic pathway is regulated by several genes belonging to FUM cluster whose behaviour in different ecological conditions was poorly studied. The aim of this work was to investigate the behaviour of 2 F. verticillioides strains grown in vitro both on a FB-inducing (Malt extract agar-MEA) and FB-inhibiting (Czapeck yeast agar-CYA) media. Fungal growth, FBs production and gene expression were studied in different temperature (T; 20-30) and water activity (aw; 0.90-0.99) regimes, in liquid cultures incubated for 7-21 days. The expression of two genes: FUM21 and FUM2 was considered; relative quantitation of gene expression was performed by RealTime (RT)-PCR. The results showed that, with aw fixed at 0.99, maximum FUM21 and FUM2 expression was observed at 30°C after 14 days of incubation, while FBs production increased from 7 to 21 days. At fixed T (25°C), fungal growth at 0.90 aw was not observed after 21 days of incubation. Gene expression increased with incubation time both at 0.95 and 0.99 aw, FB production increased till to 21 and 14 days respectively at 0.95 and 0.99 aw. In all the conditions studied the expression of the 2 genes considered followed a very similar trend, but FUM2 was much more expressed than FUM21 and more influenced by aw conditions.