Bioinformatic prediction of cis-acting elements in FUM gene promoters putatively involved in transcriptional control of fumonisins biosynthesis

Fumonisins are secondary metabolites produced by the maize pathogen Fusarium verticillioides, agent of pink ear rot; these mycotoxins cause agro-economical losses and detrimental health effects in animals and humans. The FUM genes needed for fumonisins biosynthesis are clustered and co-expressed in the fumonisins producers. In eukaryotes, coordination of gene transcription is mostly attained through transcription factors shared by co-regulated genes, whose specificity relies on the recognition of cis-regulatory elements on the promoters of their targets. A bioinformatic analysis of FUM gene promoters in F. verticillioides identified a partially degenerated motif potentially involved in the regulation of FUM genes expression, and therefore in fumonisins biosynthesis. The same oligomer was found in the clustered FUM genes of the other fumonisins producers Fusarium oxysporum and Aspergillus niger; while it is not significantly over-represented in the scattered FUM homologs of the fumonisins non-producing euascomycetes F. graminearum, A. nidulans, Magnaporthe grisea and Neurospora crassa. Comparison of the transcriptional strength of the intact FUM1 promoter and of a synthetic version, where the motif discovered had been mutated, was carried out in vivo and in planta by quantifying GFP transcripts in F. verticillioides transformants, carrying either promoter upstream of the GFP reporter. Our results show that mutation of the main motif in FUM1 promoter is sufficient to significantly impair its efficiency, thus validating our in silico approach as a discovery tool. The presence of the degenerated 6-mer in all clustered FUM genes suggests that this set of oligomers includes candidate regulatory sequences.