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

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2001

Supplementary information

Supplementary Data
Bending 1 (new)

graphic

Bending of a MT in FB1otefGFPTub1. Note that the bend MT is neither in contact with the cortex nor with other MTs suggesting that it interacts with invisible cell components.

- mov file
Supplementary Data
Bending 2 (see Fig. 7A)

graphic

Bending of MTs in FB1otefGFPTub1. MTs are focussed towards one cell pole. Cortical sliding of MTs appears to cause bending of the left bundle, demonstrating that MTs interact at the focus point. Note that bending is followed by a release and another bending.

- mov file
Supplementary Data
Bending 3 (see Fig 7C)

Bending of a MT-bundle in FB2rGFPTub1. No indications for MT interaction with the cortex is obvious, suggesting that bending results from sliding within the bundle.

- jpeg file
Supplementary Data
Mitosis (see Fig. 9A)

graphic

In FB1otefGFPTub1 a rigid bridge of spindle MTs connects two asters during anaphase B. Astral MTs have contact with the cortex and appear to exert pulling force on the spindle poles resulting in lateral motion of the aster. These forces most likely supports spindle elongation during mitosis.

- mov file
Supplementary Data
MT-motion 1 (see Fig. 7D)

graphic

Motion of a short MT along a filamentous track that appears dark as it excludes the cytoplasmic background of GFP-Tub1 fusion protein in FB1otefGFPTub1. Note that the MT has no contact with other MTs.

- mov file
Supplementary Data
MT-motion 2 (see Fig. 8A)

graphic

Formation, sliding and cortical motion of a short free MT. A MT elongates while it remains attached to another MT. The attached end slides along this MT, while the other end still elongates. As it gains contact with the cortex the short MT changes direction and subsequently detaches and rapidly moves along the cortex.

- mov file
Supplementary Data
Aster motion (see Fig. 9B)

graphic

In FB1otefGFPTub1 a rigid bridge of spindle MTs connects two asters during anaphase B. Astral MTs have contact with the cortex and appear to exert pulling force on the spindle poles resulting in lateral motion of the aster. These forces most likely support spindle elongation during mitosis.

- mov file
Supplementary Data
Nuclear positioning (see Fig. 9C)

graphic

Prior to cytokinesis, nuclei are positioned within mother and daughter cell, respectively. Dynamic astral MTs kept contact with the cortex and prominent short range motion of the asters was observed.

- mov file