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Microtubules in the fungal pathogen Ustilago maydis are highly dynamic and determine cell polarity
G Steinberg1, R Wedlich-Söldner, M Brill
1Institut für Genetik und Mikrobiologie, LMU, Maria-Ward-Strasse 1a, D-80638 Munich, Germany. Gero.Steinberg@mailer.uni-marburg.de
Abstract:
Many fungal pathogens undergo a yeast-hyphal transition during their pathogenic development that requires rearrangement of the cytoskeleton, followed by directed membrane traffic towards the growth region. The role of microtubules and their dynamic behavior during this process is not well understood. Here we set out to elucidate the organization, cellular role and in vivo dynamics of microtubules in the dimorphic phytopathogen Ustilago maydis. Hyphae and unbudded yeast-like cells of U. maydis contain bundles of spindle pole body-independent microtubules. At the onset of bud formation two spherical tubulin structures focus microtubules towards the growth region, suggesting that they support polar growth in G(2), while spindle pole body-nucleated astral microtubules participate in nuclear migration in M and early G(1). Conditional mutants of an essential alpha-tubulin gene from U. maydis, tub1, confirmed a role for interphase microtubules in determination of cell polarity and growth. Observation of GFP-Tub1 fusion protein revealed that spindle pole body-independent and astral microtubules are dynamic, with elongation and shrinkage rates comparable to those found in vertebrate systems. In addition, very fast depolymerization was measured within microtubule bundles. Unexpectedly, interphase microtubules underwent bending and rapid translocations within the cell, suggesting that unknown motor activities participate in microtubule organization in U. maydis. Movies available on-line: http://www.biologists.com/JCS/movies/jcs1792.html
Insights
Microtubules in fungal pathogens like Ustilago maydis are crucial for cell growth and polarity. Their dynamic behavior and organization are essential for pathogenic development.
Area of Science:
- Cell Biology
- Mycology
- Plant Pathology
Background:
- Fungal pathogens often switch between yeast and hyphal forms during infection.
- Cytoskeletal rearrangements, particularly microtubules, are vital for this transition and directed growth.
- The precise role and dynamics of microtubules in dimorphic fungi remain unclear.
Purpose of the Study:
- To investigate microtubule organization, function, and dynamics in the dimorphic phytopathogen Ustilago maydis.
- To understand how microtubules contribute to cell polarity and growth during pathogenic development.
Main Methods:
- Microscopy of Ustilago maydis, including live-cell imaging of GFP-Tub1 fusion protein.
- Conditional mutagenesis of the essential alpha-tubulin gene (tub1).
- Analysis of microtubule organization and dynamics in different cell cycle stages.
Main Results:
- Ustilago maydis utilizes spindle pole body-independent microtubule bundles for interphase growth and polarity.
- Astral microtubules nucleated by the spindle pole body are involved in nuclear migration.
- Conditional tub1 mutants demonstrate the importance of interphase microtubules for cell polarity.
- Microtubules exhibit dynamic behavior, including rapid depolymerization, bending, and translocation, suggesting motor protein involvement.
Conclusions:
- Microtubules play a dual role in Ustilago maydis: supporting polar growth via interphase bundles and nuclear migration via astral microtubules.
- The dynamic nature and active organization of microtubules are critical for the dimorphic transition and pathogenicity.
- Further research is needed to identify the motor proteins responsible for microtubule organization in this fungus.