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Endocytosis and exocytosis are strictly segregated at the ends of hyphal cells of filamentous fungi, with a collar of endocytic activity encircling the growing cell tip, which elongates through directed membrane fusion. It has been proposed that this separation supports an endocytic recycling pathway that maintains polar localization of proteins at the growing apex. In a search for proteins in the filamentous fungus Aspergillus nidulans that possess an NPFxD motif, which signals for endocytosis, a Type 4 P-Type ATPase was identified and named DnfA. Interestingly, NPFxD is at a different region of DnfA than the same motif in the Saccharomyces cerevisiae ortholog, although endocytosis is dependent on this motif for both proteins. DnfA is involved in asexual sporulation and polarized growth. Additionally, it is segregated within the Spitzenkörper from another Type 4 P-type ATPase, DnfB. Next, the phosphatidylserine marker GFP::Lact-C2 was expressed in growing hyphae, which revealed that this phospholipid is enriched on the cytosolic face of secretory vesicles. This distribution is affected by deleting either dnfA or dnfB. These findings provide evidence for the spatial and temporal segregation of Type4-ATPases in filamentous fungi, and the asymmetric distribution of phosphatidylserine to the Spitzenkörper in A. nidulans.
Schultzhaus et al. (Fri,) studied this question.