ausblenden:
Schlagwörter:
-
Zusammenfassung:
Transition between different morphological shapes is an essential step during development in many organisms. In the phytopathogenic basidiomycete Ustilago maydis the transition between yeast-like and filamentous growth is crucial for pathogenic development. It has been shown that the mRNA-binding Protein Rrm4 plays an important role in mRNA-distribution during the establishment of unipolar growth. In rrm4-mutants unconventional secretion of the chitinase Cts1 is defective. Although the main chitinase activity relies on Cts1, its biological role is still unknown. Besides cts1 also mRNAs of mitochondrial Proteins have been identified as targets of Rrm4. rrm4-mutants exhibit an increased production of mitochondrial superoxide which implies defects of the respiratory chain. Thus, it is assumed that Rrm4-dependent mRNA-transport affects protein import dynamics and the assembly of respiratory chain complexes. In this study, the chitinolytic machinery of U. maydis was investigated aiming to identify the biological function of chitinases. Thereby it was shown that the partly redundant chitinases Cts1 and Cts2 degrade remnant chitin in the division zone during yeast-like growth and thus contribute to cell separation. However both chitinases differ in their substrate cleavage site specificity. During filamentous growth only Cts1 is active and localizes in specific patterns mainly in the empty sections at the basal pole. There it also contributes to chitin degradation and thereby prevents aggregation of filaments. The unconventional secretion of Cts1 depends on septation events, whereas there might exist a second putative secretion mechanism in filaments. Besides the chitinolytic machinery, the influence of Rrm4 on mitochondrial protein import was investigated. The analysis of respiratory chain complexes by blue native gel electrophoresis however, did not show differences in the size or amount of the complexes. The analysis of protein import dynamics by live-cell imaging failed due to stochastic long-range motility of mitochondria into the bleaching area. Therefore the fluorescent marker proteins mEos2 and sfGfp were established to investigate dynamic processes in U. maydis.
