The Ca²⁺-binding penta-EF-hand protein PEF-1 is part of a fungal resistance mechanism against cell fusion-induced lysis and membrane-destabilizing antifungals

To establish a mycelial colony, germinating vegetative spores of Neurospora crassa fuse with each other and form a supracellular network. Fusion pore formation involves highly controlled cell wall breakdown and plasma membrane merger. These steps bear the risk of cell lysis and death by membrane rupture.

We identified the Ca²⁺-binding penta-EF-hand protein PEF-1 as part of a proposed membrane repair mechanism. Subcellular localization and live-cell imaging revealed that PEF-1 is recruited to the fusion point of lysing germling pairs. Additionally, PEF-1 accumulates at the plasma membrane after treatment with antifungal and membrane-destabilizing drugs, such as nystatin or the plant defense compound tomatine. The treatment with tomatine also results in PEF-1 recruitment to septa and occlusion of the septal pore. Consistent with this finding, the growth of a pef-1 knock-out mutant on medium containing tomatine is highly impaired, compared to the wild type strain.

In addition, PEF-1 functions appear to be conserved in the fungal kingdom. For example, the PEF-1 homologue of the grey mold Botrytis cinerea also shows membrane recruitment after tomatine treatment. Moreover, our data indicate that Pef-1p, as part of a repair mechanism, promotes survival of the human fungal pathogen Candida albicans inside of macrophages.

We hypothesize that, membrane damage results in the influx of calcium, which activates PEF-1, which in turn mediates plasma membrane repair. Further studies aim to characterize the molecular bases of this repair mechanism in different fungi. Since PEF-1 mediates resistance to the phytoanticipin tomatine, we are currently also testing its contribution to fungal virulence using B. cinerea as a model. Further studies will also investigate the role of Pef-1p -as a potential pathogenicity factor- during infections by C. albicans.