The plant pathogenic fungus Ustilago maydis induces disease only in its dikaryotic stage that is generated after mating. This process involves coordinated cAMP and mitogen-activated protein kinase signalling to regulate transcriptional as well as morphological responses. Among the induced products is the key regulator for pathogenic development. Recent advances identified crucial nodes that interconnect these pathways. The key regulator orchestrates a complex transcriptional cascade, the components of which have been uncovered by genomic strategies. This is complemented by insights into organization, dynamics and function of the cytoskeleton, which begin to establish the links between signalling, intracellular transport processes and morphology.