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ORIGINAL RESEARCH article

Front. Fungal Biol.
Sec. Fungal Genomics and Evolution
Volume 5 - 2024 | doi: 10.3389/ffunb.2024.1505388
This article is part of the Research Topic Highlights of the 16th European Conference on Fungal Genetics (Innsbruck, 5-8th March 2023) View all articles

CSE-8, a filamentous fungus-specific Shr3-like chaperone, facilitates endoplasmic reticulum exit of chitin synthase CHS-3 (class I) in Neurospora crassa

Provisionally accepted
Samantha Veronica González-Téllez Samantha Veronica González-Téllez Meritxell Riquelme Meritxell Riquelme *
  • Center for Scientific Research and Higher Education in Ensenada (CICESE), Ensenada, Mexico

The final, formatted version of the article will be published soon.

    Chitin is a crucial structural polysaccharide in fungal cell walls, essential for maintaining cellular plasticity and integrity. Its synthesis is orchestrated by chitin synthases (CHS), a major family of transmembrane proteins. In Saccharomyces cerevisiae, the cargo receptor Chs7, belonging to the Shr3-like chaperone family, plays a pivotal role in the exit of Chs3 from the endoplasmic reticulum (ER) and its subsequent activity in the plasma membrane (PM). However, the auxiliary machinery responsible for CHS trafficking in filamentous fungi remains poorly understood. The Neurospora crassa genome encodes two orthologues of Chs7: chitin synthase export (CSE) proteins CSE-7 (NCU05720) and CSE-8 (NCU01814), both of which are highly conserved among filamentous fungi. In contrast, yeast forms only possess a single copy CHS export receptor. Previous research highlighted the crucial role of CSE-7 in the localization of CHS-4 at sites of cell wall synthesis, including the Spitzenkörper (SPK) and septa. In this study, CSE-8 was identified as an export protein for CHS-3 (class I). In the ∆cse-8 knockout strain of N. crassa, CHS-3-GFP fluorescence was absent from the SPK or septa, indicating that CSE-8 is required for the exit of CHS-3 from the ER. Additionally, sexual development was disrupted in the ∆cse-8 strain, with 20% of perithecia from homozygous crosses exhibiting two ostioles. A ∆cse-7;∆cse-8 double mutant strain showed reduced N-acetylglucosamine (GlcNAc) content and decreased radial growth. Furthermore, the loss of cell polarity and the changes in subcellular distribution of CSE-8-GFP and CHS-3-GFP observed in hyphae under ER stress induced by the addition of tunicamycin and dithiothreitol reinforce the hypothesis that CSE-8 functions as an ER protein. The current evidence suggests that the biogenesis of CHS exclusive to filamentous fungi may involve pathways independent of CSE-mediated receptors.

    Keywords: Chitin synthases, endoplasmic reticulum, cargo receptor protein, Spitzenkörper, ER chaperone, perithecia CHS, chitin synthases, CSE, chitin synthase export protein, ER, endoplasmic reticulum, GFP, green fluorescent protein, PM, plasma membrane, SPK, Spitzenkörper, LSCM, Laser scanning confocal microscopy, SDCM, spinning disc confocal microscopy

    Received: 02 Oct 2024; Accepted: 18 Dec 2024.

    Copyright: © 2024 González-Téllez and Riquelme. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Meritxell Riquelme, Center for Scientific Research and Higher Education in Ensenada (CICESE), Ensenada, Mexico

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