Lichtregulation der Genexpression und Entwicklung in Ustilago maydis

In this thesis the largely unknown photobiology of the basidiomycete Ustilago maydis was investigated. Transcriptomic analysis showed that dark-adapted U. maydis sporidia were able to perceive monochromatic blue, red and far-red light and in response regulated the expression of numerous genes. In FB1 wild-type, in total 404 genes were differentially expressed in one or more light conditions, which corresponds to around 5.9 % of the protein coding genes in U. maydis. White collar 1 (Wco1) was identified as the essential photoreceptor for blue light conditions and phytochrome (Phy1) as photoreceptor for red and far-red light conditions, respectively. But Wco1 also influenced the gene expression in red and far-red light and Phy1 had an effect on the number of differentially expressed genes in blue light. Additionally, both photoreceptors also showed a light-independent function. Functional analysis revealed many blue light-regulated genes with a role in oxidation-reduction processes and also metabolism was affected by genes differentially expressed among all three light conditions. Furthermore, expression of genes for the synthesis of ferrichromes was regulated by Wco1 in the dark. Localization studies showed Wco1 and Wco2 mainly in the nucleus and in less concentration in the cytoplasm. Phy1 on the other hand was found nearly exclusively in the cytoplasm. No evidence for a direct interaction of Wco1, Wco2 and Phy1 was found by yeast-two-hybrid analysis. Next to the light effect on gene expression the importance of light, Wco1 and Phy1 for the development of U. maydis was investigated. Blue and red light showed a minor inhibitory effect on the formation of conjugation tubes and this light-dependency was abolished in ∆wco1 and ∆phy1 deletion mutants. Neither treatment with several light conditions nor the deletion of Wco1 or Phy1 had an impact on the ability of compatible U. maydis cells to form filaments. Lastly, pathogenicity was slightly reduced in ∆wco1 compared to wild-type. Thus, light and the photoreceptors Wco1 and Phy1 only had a low regulatory effect on development, at least in the experimental conditions used in the presented studies.