Using fimbrin to quantify the endocytic subapical collar during polarized growth in three filamentous fungi

ABSTRACT

Filamentous fungi produce specialized cells called hyphae. These cells grow by polarized extension at their apex, which is maintained by the balance of endocytosis and exocytosis at the apex. Although endocytosis has been well characterized in other organisms, the details of endocytosis and its role in maintaining polarity during hyphal growth in filamentous fungi is comparatively sparsely studied. In recent years, a concentrated region of protein activity that trails the growing apex of hyphal cells has been discovered. This region, dubbed the “endocytic collar” (EC), is a dynamic 3-dimensional region of concentrated endocytic activity, the disruption of which results in the loss of hyphal polarity. Here, fluorescent protein–tagged fimbrin was used as a marker to map the collar during growth of hyphae in three fungi: Aspergillus nidulans, Colletotrichum graminicola, and Neurospora crassa. Advanced microscopy techniques and novel quantification strategies were then utilized to quantify the spatiotemporal localization and recovery rates of fimbrin in the EC during hyphal growth. Correlating these variables with hyphal growth rate revealed that the strongest observed relationship with hyphal growth is the distance by which the EC trails the apex, and that measured endocytic rate does not correlate strongly with hyphal growth rate. This supports the hypothesis that endocytic influence on hyphal growth rate is better explained by spatiotemporal regulation of the EC than by the raw rate of endocytosis.

KEYWORDS:

• Endocytic collar
• endocytosis
• hyphal growth
• polarity

ACKNOWLEDGMENTS

We thank James Taylor and Dr. Charles Kenerley for providing the pFPL-Rh plasmid originally created by Dr. Mark Farman, and Dr. Rosa Mouriño-Pérez for providing the Neurospora FIM-1::sGFP strain.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

SUPPLEMENTARY MATERIAL

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00275514.2023.2202689.

Additional information

Funding

This work was also supported in part by U.S. Department of Agriculture National Institute of Food and Agriculture (USDA NIFA) project [TEX0-1-9018].