Self-protection against the sphingolipid biosynthesis inhibitor fumonisin B1 is conferred by a FUM cluster-encoded ceramide synthase

Authors: JANEVSKA, SLAVICA - Hans-Knoll Institute; LULIIA, FERLING - Hans-Knoll Institute; RAUTSCHEK, JULIA - Hans-Knoll Institute; HOEFGEN, SANDRA - Hans-Knoll Institute; Proctor, Robert; HILLMAN, FALK - Hans-Knoll Institute; VALIANTE, VITO - Hans-Knoll Institute

Submitted to: mBio
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2020
Publication Date: 6/16/2020
Citation: Janevska, S., Luliia, F., Rautschek, J., Hoefgen, S., Proctor, R.H., Hillman, F., Valiante, V. 2020. Self-protection against the sphingolipid biosynthesis inhibitor fumonisin B1 is conferred by a FUM cluster-encoded ceramide synthase. mBio. 11(3):e00455-20. https://doi.org/10.1128/mBio.00455-20.
DOI: https://doi.org/10.1128/mBio.00455-20

Interpretive Summary: Fumonisins are a group of fungal toxins that frequently contaminate corn, and as a result pose health risks to people, pets, and livestock that eat corn-base food or feed. Fumonisins are toxic because they inhibit an enzyme, ceramide synthase, that is required for formation of sphingolipids, a group of lipids that is essential for normal functioning of animal, plant, and fungal cells. Because sphingolipids are an essential component of fungal cells, fungi that produce fumonisins must have a mechanism to protect themselves from the toxins. Therefore, in this study, we determined how the fungus Fusarium verticillioides, the predominant cause of fumonisin contamination in corn, protects itself from the toxins. We found that F. verticillioides has five genes that serve as blue prints for ceramide synthases. Two of the genes, FUM17 and FUM18, are located on a F. verticillioides chromosome in a region that includes all of the genes required for synthesis of fumonisins. We also found that FUM18, but not FUM17, is required for normal levels of fumonisin self-protection exhibited by F. verticillioides. Furthermore, we found that the FUM18 protein can function as a ceramide synthase by itself, but the FUM17 protein requires another protein to function as a ceramide synthase. These results indicate that the FUM18 ceramide synthase helps protect F. verticillioides from the toxic effects of fumonisins. Such knowledge has potential to contribute to strategies to protect humans and animals from the health hazards posed by fumonisins.

Technical Abstract: Fumonisin (FB) mycotoxins are produced by some species of the fungus Fusarium and have detrimental effects on human and animal health through their ability to inhibit the sphingolipid biosynthetic enzyme ceramide synthase (CS). Because sphingolipids are an essential component of eukaryotic cells, FB-producing fungi require a mechanism to protect themselves from the toxins. Here, we investigated whether an ABC transporter gene (FUM19) and two CS genes (FUM17 and FUM18) in the FB biosynthetic gene (FUM) cluster in Fusarium verticillioides contribute to FB self-protection. FUM19 deletion induced expression of other FUM cluster genes and increased FB1 production, whereas FUM19 overexpression repressed FUM gene expression. Deletion of FUM18 increased sensitivity of F. verticillioides to the fumonisin analog FB1, while heterologous expression of the gene increased FB1 tolerance in wild-type Saccharomyces cerevisiae. By themselves, FUM18 and two other F. verticillioides CS genes, CER2 and CER3, complemented a S. cerevisiae CS null mutant, whereas FUM17 and CER3, another F. verticillioides CS gene, did not complement the mutant by themselves, but did complement when introduced into the mutant together. Our results indicate that FUM cluster genes contribute to FB-self-protection in two ways. First, FUM19 indirectly contributes to self-protection by modulating levels of FB through its effects on expression of FUM cluster genes. Second, FUM18 provides more direct protection, presumably by providing additional copies of CS. These findings provide insight into FB-self-protection in fungi and point to novel methods for CS-related drug discovery.