Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2011
Publication Date: 3/11/2011
Citation: Breakspear, A., Pasquali, M., Broz, K.L., Dong, Y., Kistler, H.C. 2011. Npc1 is involved in sterol trafficking in the filamentous fungus Fusarium graminearum. Fungal Genetics and Biology. 48:725-730. Interpretive Summary: The process by which pathogenic fungi make sterols has been exploited for the control of fungal diseases of both plants and animals. Two important classes of fungicides, the allylamines and azoles, each inhibit different steps in the synthesis of the major fungal sterol known as ergosterol, which is related to the human sterol cholesterol. Despite the importance of these compounds and their action for control of fungal diseases, little is known about regulation of sterol synthesis and transport within cells of filamentous fungi. This study describes a fungal gene which controls the process by which ergosterol is moved within the cell to its final destination in the outer layer of the cell. Strains of the fungus created lacking the gene were less pathogenic to plants and more sensitive to fungicides. Because of the importance of ergosterol biosynthesis as a target for antifungal therapy of human and plant diseases, further knowledge of ergosterol utilization and movement is warranted. Information generated by this work will be used by other scientists involved in fungicide improvement and control of fungal diseases by use of antifungal compounds.
Technical Abstract: The ortholog of the human gene NPC1 was identified in the plant pathogenic, filamentous fungus Fusarium graminearum by shared amino acid sequence, protein domain structure and cellular localization of the mature fungal protein. The Fusarium Npc1 gene shares 34% amino acid sequence identity and 51% similarity to the human gene, has similar domain structure and is constitutively expressed, although up-regulated in ungerminated macroconidia and ascospores. GFP-tagged Npc1p localizes to the fungal vacuolar membrane. Cultures derived from a 'npc1 mutant strain contain significantly more ergosterol than cultures of the wild type. Staining with the fluorescent, sterol binding dye filipin, shows that ergosterol accumulates in vacuoles of the 'npc1 mutant but not the wild type strain. The 'npc1 mutant has a temperature dependent reduction in growth and greater sensitivity to the ergosterol synthesis inhibiting fungicide tebuconazole compared with the wildtype strain or the mutant complemented with wild type Npc1. The mutant also is significantly reduced in pathogenicity to wheat. Our results are consistent with the interpretation that Npc1p is important for normal transport of ergosterol from the vacuole and is essential for proper membrane function under particular environmental conditions.