Submitted to: Eukaryotic Cell
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/9/2007
Publication Date: 11/15/2007
Citation: Oide, S., Krasnoff, S., Gibson, D.M., Turgeon, G. 2007. Intracellular siderophores are essential for ascomycete sexual development in heterothallic Cochliobolus heterostrophus and homothallic Gibberella zeae. Eukaryotic Cell. 6:1339-1353. Interpretive Summary: Genome-wide searches of fungal systems have revealed a number of genes involved in secondary metabolites for which no products are known. Nonribosomally derived peptide synthetases (NRPSs) are one gene family involved in forming secondary peptide metabolites, and these genes may play major roles in fungal development and virulence. In this study, we sought to define the products of a particular gene, NRPS2, and understand its role in fungal morphology and development in two different fungi. We found that NPRS2 is responsible for the synthesis of a highly conserved iron-binding peptide, ferrocrocin, found within the cell that is involved in regulating iron metabolism. The results of this study establish that iron and ferricrocin are essential for successful sexual development of both fungi.
Technical Abstract: Connections between fungal development and secondary metabolism have been reported previously, but as yet, no comprehensive analysis of a family of secondary metabolites and their possible role in fungal development has been reported. In the present study, mutant strains of the heterothallic ascomycete, Cochliobolus heterostrophus, each lacking one of twelve genes (NPS1 to NPS12) encoding a non-ribosomal peptide synthetase (NRPS), were examined for a role in sexual development. One type of strain (Dnps2) was defective in ascus/ascospore development in homozygous Dnps2 crosses. Homozygous crosses of the remaining eleven Dnps strains showed wild-type fertility. Phylogenetic, expression, and biochemical analyses demonstrated that the NRPS encoded by NPS2 is responsible for biosynthesis of ferricrocin, the intracellular siderophore of C. heterostrophus. Functional conservation of NPS2 in both heterothallic C. heterostrophus and the unrelated, homothallic, ascomycete Gibberella zeae was demonstrated. G. zeae Dnps2 strains are defective, concomitantly, in intracellular siderophore (ferricrocin) biosynthesis and sexual development. Exogenous application of iron partially restored fertility to C. heterostrophus and G. zeae Dnps2 strains, demonstrating that abnormal sexual development of Dnps2 strains is at least partly due to their iron deficiency. Exogenous application of the natural siderophore, ferricrocin, to C. heterostrophus and G. zeae Dnps2 strains restored WT fertility. NPS1 a G. zeae NPS gene that groups, phylogenetically, with NPS2, does not play a role in sexual development. Overall, these data demonstrate that iron and intracellular siderophores are essential for successful sexual development of the heterothallic ascomycete C. heterostrophus and homothallic ascomycete G. zeae.