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Septum-directed secretion in the filamentous fungus Aspergillus oryzae

Yugo Hayakawa1, Eri Ishikawa, Jun-Ya Shoji

  • 1Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.

Molecular Microbiology
|May 14, 2011
PubMed

Insights

Fungal cells perform exocytosis not only at hyphal tips but also at septa. This non-tip exocytosis is crucial for delivering proteins like AoUapC and AoGap1 to the fungal cell.

Area of Science:

  • Cell Biology
  • Mycology
  • Molecular Biology

Background:

  • Exocytosis, the process of vesicle fusion with the plasma membrane, is known to occur at hyphal tips in fungal cells.
  • Circumstantial evidence suggests exocytosis may also occur at other cellular sites, such as fungal septa.

Purpose of the Study:

  • To investigate the occurrence and characteristics of exocytosis at fungal septa.
  • To determine if exocytosis at septa differs from that at hyphal tips.

Main Methods:

  • Monitoring the dynamics of EGFP-fused α-amylase (AmyB-EGFP) in Aspergillus oryzae.
  • Analyzing the requirement of microtubules and F-actin for protein accumulation at septa.
  • Utilizing fluorescence recovery after photobleaching (FRAP) to study secretory vesicle fusion at septa.
  • Tracking the localization of plasma membrane transporters (AoUapC, AoGap1).

Main Results:

  • AmyB-EGFP accumulated at both hyphal tips and septal periplasm.
  • Septal accumulation of AmyB-EGFP required microtubules but not F-actin, differing from tip exocytosis.
  • Secretory vesicles were observed to fuse with the septal plasma membrane.
  • Plasma membrane transporters AoUapC and AoGap1 preferentially accumulated at septa and lateral membranes, not apical regions.

Conclusions:

  • Exocytosis occurs at fungal septa in addition to hyphal tips.
  • Non-tip directed exocytosis at septa is important for the delivery of specific proteins.
  • This finding expands our understanding of protein trafficking and secretion in filamentous fungi.

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