Abstract
Recent research in filamentous fungi has revealed that the motility of an endocytic organelle early endosome (EE) has a versatile role in many physiological functions. Here, to further examine the motility of EEs in the industrially important fungus Aspergillus oryzae, we visualized these organelles via the Rab5 homolog AoRab5 and identified AoHok1, a putative linker protein between an EE and a motor protein. The Aohok1 disruptant showed retarded mycelial growth and no EE motility, in addition to an apical accumulation of EEs and peroxisomes. We further demonstrated that the Aohok1 disruptant exhibited less sensitivity to osmotic and cell wall stresses. Analyses on the protein secretory pathway in ΔAohok1 cells showed that, although distribution of the endoplasmic reticulum and Golgi was not affected, formation of the apical secretory vesicle cluster Spitzenkörper was impaired, probably resulting in the observed reduction of the A. oryzae major secretory protein α-amylase. Moreover, we revealed that the transcript level of α-amylase-encoding gene amyB was significantly reduced in the Aohok1 disruptant. Furthermore, we observed perturbed conidial and sclerotial formations, indicating a defect in cell differentiation, in the Aohok1 disruptant. Collectively, our results suggest that EE motility is crucial for α-amylase production and cell differentiation in A. oryzae.
Highlights
The early endosome (EE) is an organelle in the endocytic pathway in filamentous fungi that is constantly moved along the microtubule (MT) by two motor proteins, kinesin and dynein[1]
Similar motility was observed for the plasma membrane purine transporter AoUapC tagged with EGFP, which was colocalized with the endocytic marker dye FM4-64, when endocytosis was induced in A. oryzae cells[19]
To further identify the moving dots labelled with EGFP-AoRab[5], we co-stained the cells with FM4-64
Summary
The early endosome (EE) is an organelle in the endocytic pathway in filamentous fungi that is constantly moved along the microtubule (MT) by two motor proteins, kinesin and dynein[1]. By analyzing the disruptant of Aohok[1], which encodes an ortholog of Hook, we confirmed that ΔAohok[1] cells showed the same phenotypes of EE and PO distribution as observed in disruptants of U. maydis and A. nidulans. These results suggest that EE motility is crucial for abundant α-amylase production and proper cell differentiation in A. oryzae.
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