The Aspergillus nidulans Peripheral ER: Disorganization by ER Stress and Persistence during Mitosis

Ane Markina-Iñarrairaegui,Miguel A Peñalva,Areti Pantazopoulou,Eduardo A Espeso,Jae-Hyuk Yu

doi:10.1371/journal.pone.0067154

Ane Markina-Iñarrairaegui, Miguel A Peñalva + Show 3 more

Open Access

https://doi.org/10.1371/journal.pone.0067154

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Abstract

The genetically amenable fungus Aspergillus nidulans is well suited for cell biology studies involving the secretory pathway and its relationship with hyphal tip growth by apical extension. We exploited live-cell epifluorescence microscopy of the ER labeled with the translocon component Sec63, endogenously tagged with GFP, to study the organization of ‘secretory’ ER domains. The Sec63 A. nidulans ER network includes brightly fluorescent peripheral strands and more faintly labeled nuclear envelopes. In hyphae, the most abundant peripheral ER structures correspond to plasma membrane-associated strands that are polarized, but do not invade the hyphal tip dome, at least in part because the subapical collar of endocytic actin patches constrict the cortical strands in this region. Thus the subapical endocytic ring might provide an attachment for ER strands, thereby ensuring that the growing tip remains ‘loaded’ with secretory ER. Acute disruption of secretory ER function by reductive stress-mediated induction of the unfolded protein response results in the reversible aggregation of ER strands, cessation of exocytosis and swelling of the hyphal tips. The secretory ER is insensitive to brefeldin A treatment and does not undergo changes during mitosis, in agreement with the reports that apical extension continues at normal rates during this period.

Highlights

A remarkable aspect of the biology of filamentous fungi is their ability to grow exclusively by apical extension
Morphology of the A. nidulans ER Visualized with Endogenously Tagged Sec63
Sec63-GFP localizes to a network of ‘strands’ corresponding to the different ER ‘domains’ reported in yeast [14], namely nuclear envelopes (NEs) and ‘peripheral’ ER, including pm-associated ER strands and a faint network of interconnecting tubules (Figure 1)

Summary

Introduction

A remarkable aspect of the biology of filamentous fungi is their ability to grow exclusively by apical extension. Sec63-GFP localizes to a network of ‘strands’ corresponding to the different ER ‘domains’ reported in yeast [14], namely nuclear envelopes (NEs) and ‘peripheral’ ER, including pm-associated ER strands and a faint network of interconnecting tubules (Figure 1).

Results

Conclusion