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Vol. 16, Issue 6, 2746-2758, June 2005
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Max-Planck-Institut für terrestrische Mikrobiologie, D-35043 Marburg, Germany
Submitted March 1, 2005;
Revised March 31, 2005;
Accepted April 1, 2005
Monitoring Editor: David Drubin
Fungal pathogenicity often involves a yeast-to-hypha transition, but the structural basis for this dimorphism is largely unknown. Here we analyze the role of the cytoskeleton in early steps of pathogenic development in the corn pathogen Ustilago maydis. On the plant yeast-like cells recognize each other, undergo a cell cycle arrest, and form long conjugation hyphae, which fuse and give rise to infectious filaments. F-actin is essential for polarized growth at all these stages and for cell-cell fusion. Furthermore, F-actin participates in pheromone secretion, but not perception. Although U. maydis contains prominent tubulin arrays, microtubules are neither required for cell-cell recognition, nor for cell-cell fusion, and have only minor roles in morphogenesis of yeast-like cells. Without microtubules hyphae are formed, albeit at 60% reduced elongation rates, but they reach only 
50 µm in length and the nucleus fails to migrate into the hypha. A similar phenotype is found in dynein mutants that have a nuclear migration defect and stop hyphal elongation at 50 µm. These results demonstrate that microtubules are dispensable for polarized growth during morphological transition, but become essential in long-distance hyphal growth, which is probably due to their role in nuclear migration.
Abbreviations used: MT, microtubule; F-actin, filamentous actin; GFP, green fluorescent protein; CFP, cyan-shifted fluorescent protein; YFP, yellow-shifted fluorescent protein; aa, amino acids.
Address correspondence to: Gero Steinberg (Gero.Steinberg{at}staff.uni-marburg.de).
This article has been cited by other articles:
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