Overexpression of NRPS4 leads to increased surface hydrophobicity in Fusarium graminearum

The plant pathogen Fusarium graminearum is the infamous cause of Fusarium head blight worldwide resulting in significant losses of yield and reduced grain feed quality. It also has the potential to produce a range of small bioactive peptides produced by the nonribosomal peptide synthetases (NRPSs). Most of these are unknown as F. graminearum contains 19 NRPS encoding genes, but only 3 have been assigned products. For the first time, we use deletion and overexpression mutants to investigate the functions and product of NRPS4 in F. graminearum. Deletion of NRPS4 homologues in Alternaria brassicicola and Cochloibolus heterostrophus has been shown to result in mutants unable to repel water. In a time study of surface hydrophobicity we observed that water droplets could penetrate seven day old colonies of the NRPS4 deletion mutants. Loss in ability to repel water was first observed on 13 days old cultures of the wild type strain, whereas the overexpression strain remained water repellant throughout the 38 day time study. The conidia of both mutants were examined and those of the overexpression mutant showed distinct morphological differences in form of collapsed cells. These observations might suggest that the peptide product of NRPS4 could be an architectural factor in the cell walls of Fusarium or an indirect regulator of hydrophobicity.