The phytopathogenic fungus Ustilago maydis is a heterobasidiomycete belonging to the order Ustilaginales and the family Ustilaginaceae. U. maydis It's host range is limited to maize (Zea mays) and Teosinte (Zea mays ssp. mexicana und Zea mays ssp. pavigluminis). After infection of the maize plant characteristical disease symptoms are induced, those have been first described by Bonnet in 1754. These range from the formation of chloroses and anthocyan production to the formation of tumors on all plant parts abouve ground. The tumors crack open and release the black teliospores, the resulting burnt look of the plant has been eponymous to the disease's name.
Although U. maydis has only a minor economic impact, the organism has become one of the most important model organisms for phytopathogenic fungi during the last decades. It's dimorphic life cycle, divided into a saprophytic and a biotrophic phase, can be reconstructed under laboratory conditions in only 3 to 4 weeks. Additionaly it is possible to cultivate U. maydis during it's saprophytic growth phase on synthetic media, and to address the organism with a multitude of molecular methods. Protocols for effective transformation of self-replicating plasmids as well as integration of DNA-sequences by homologous recombination have been established. Several antibiotic resistances and auxotrophic markers are available, and regulable gene expression is possible with the promotors nar1 and crg1, which are controllable by nitrate- or carbon source respectively. Sequencing of the 20 Mb genome is finsihed and the sequences are publicly available (Kämper et al., 2006), this allows in silico approaches, e.g. identification of homologuos genes that are already known from other organisms. All these powerful tools for the molecular analysis of U. maydis in combination with its similarities to a multitude of phyto- as well as humanpathogenic fungi render this organism an ideal candidate for the analysis of fungal infections.