Identification and analysis of cis-acting regulatory motifs on the promoter of FUM1, a key fumonisin biosynthetic gene of Fusarium verticillioides

Fumonisins are mycotoxins -produced mainly by Gibberella moniliformis (anamorph Fusarium verticillioides, Fv)- that contaminate maize and maize-based products and cause great concern for human and animal health. Several biosynthetic (FUM) genes are known; among them, FUM1 encodes a key polyketide synthase indispensable for fumonisin synthesis, and whose transcripts are always detectable when these metabolites are produced. To study the genetic and environmental factors linked to fumonisin production, we performed bioinformatic analyses on the putative promoter sequences of all known FUM genes, which are known to be co-regulated at the transcriptional level. Results suggested the presence of a 6-bp sequence statistically over-represented in the promoters of the genes in the FUM cluster compared to the rest of the genome. This motif could cis-act on the regulation of the FUM genes and notably of FUM1, since it is repeated twice in its putative promoter sequence (pFUM1). To validate the in silico prediction, a wt pFUM1 sequence from a toxigenic Fv strain and a synthetic version where this motif is mutated (mut-pFUM1) were obtained. Both pFUM1 and mut-pFUM1 were used to drive the expression of GFP in transgenic Fv strains. Transcript quantification of the endogenous FUM1 and of GFP by RT-qPCR in both Fv transformants is under way, and will allow us to confirm the importance of the identified motif for wild-type expression of FUM1 under various conditions.