Microtubules are dispensable for the initial pathogenic development but required for long-distance hyphal growth in the corn smut fungus Ustilago maydis.

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.