Cellular iron utilization is regulated by putative siderophore transporter FgSit1 not by free iron transporter in Fusarium graminearum

This report investigated FgSit1, which encodes a putative ferrichrome transporter of Fusarium graminearum. The identity of the deduced amino acid sequence of FgSit1 with the amino acid sequence of ScArn1p, an FC-Fe3+ transporter of Saccharomyces cerevisiae, was 51%; both the growth defect related to the Δfet3Δarn1-4 strain of S. cerevisiae in an iron-depleted condition and the FC-Fe3+ uptake activity were recovered upon the introduction of FgSit1 into the Δfet3Δarn1-4 strain. Although ScArn1p was found in the late endosomal compartment in S. cerevisiae, FgSit1 was found on the plasma membrane in S. cerevisiae; when FgSit1 was expressed exogenously in S. cerevisiae, it showed greater FC-Fe3+ uptake activity than did ScArn1p. Additionally, in F. graminearum FC-Fe3+ uptake activity in the Δfgsit1 strain was found to be one-fourth that of the wild-type. However, Fe3+ uptake activity in the Δfgsit1 strain was 5-fold higher than that of wild-type; the gene expression of FgFtr1, a putative iron transporter, was induced by the deletion of FgSit1, but was not induced by the deletion of FgSit2. Taken together, these results strongly suggest that FgSit1 encodes a putative FC-Fe3+ transporter that mediates FC-Fe3+ uptake using a different mechanism than ScArn1p and plays an important role in the regulation of cellular iron availability in F. graminearum.