The Aspergillus niger RmsA protein

Abstract

Many cells and organisms go through polarized growth phases during their life. Cell polarization is achieved by local accumulation of signaling molecules which guide the cytoskeleton and vesicular trafficking to specific parts of the cell and thus ensure polarity establishment and maintenance. Polarization of signaling molecules is also fundamental for the lifestyle of filamentous fungi such as Aspergillus niger and essential for their morphogenesis, development and survival under environmental stress conditions. Considerable advances in our understanding on the protagonists and processes mediating polarized growth in filamentous fungi have been made over the past years. However, how the interplay of different signaling pathways is coordinated has yet to be determined. We found that the A. niger RmsA protein is central for the polarization of actin at the hyphal tip but also of vital importance for the metabolism, viability and stress resistance of A. niger. This suggests that RmsA could occupy an important position in the global network of pathways that balance growth, morphogenesis and survival of A. niger.

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Acknowledgements

This project was carried out within the research programme of the Kluyver Centre for Genomics of Industrial Fermentation which is part of the Netherlands Genomics Initiative/Netherlands Organization for Scientific Research.

Figures and Tables

Figure 1 Phenotypic analyses of ramosa-1 and the wild type strain T312. (A) Spores of both strains were allowed to germinate for 17 h at 25°C, after which the temperature was set to 37°C for 4 h. Hyphae were stained with 2 µM FUN-1 and subjected to microscopy using FITC and dsRed filters. FUN-1 stains nucleic acids yielding to a diffuse green cytoplasmic fluorescence. Only metabolic active cells transport FUN-1 to the vacuole and convert it to red fluorescent CIVS.9 A control staining is shown in the lower panel where the wt strain was heat-inactivated for 4 h at 50°C. Bar, 10 µm. (B) 10⁴ spores of both strains were point-inoculated on minimal agar plates containing 500 mM of different salts. Control plates did not contain any additional supplements (upper). Plates were incubated at 25°C for 4 days or at 37°C for 3 days. (C) 5 × 10⁵ spores of both strains were evenly spread on minimal agar plates. A Whatman paper disc was wetted with 5 µl of a 30% H₂O₂ solution and the plates were incubated at 37°C for 3 days.

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