Mechanistische Grundlagen uniparentaler mitochondrialer DNA-Vererbung
Final Report Abstract
A major achievement of the research project was the finding of mitoribosomal proteins as interaction partners of Mrb1. The ability of Mrb1 (p32) to bind to multiple subunits suggests a function as a protein assembly factor. Hereby, putative MRPL35 (UMAG_03337) represents a novel candidate, which has not yet been identified to interact with p32 family proteins. Based on recent insight into the role of mammalian p32 in mitochondrial (mt) translational fidelity, this finding suggests an analogous function of Mrb1 with respect to control of uniparental mtDNA inheritance (UPI). Proteomic analysis has confirmed that Mrb1 is not critical for yeast-like growth of U. maydis, specifying a role of Mrb1 under mt stress conditions. With regards to the function of Rga2, two interesting potential interaction partners were identified. Firstly, a homologue of Mdm12 (UMAG_01549), which in yeast is the major component of the mitochore complex, and secondly, a potential mitochondria-associated Zn2Cys6 zinc finger transcription factor (UMAG_12255). To discriminate between the relevance of these two candidates, detailed knowledge of their subcellular localization as well as of the submitochondrial localization of Rga2 will be mandatory. Hereby, the possibility that Rga2 is targeted to the IMS deserves further investigation. With regards to the identification of potential Lga2 complexes, conditions have been identified to release mt proteins, however, subsequent purification steps were not successful. Consistent with a specific Lga2 target in U. maydis, conditional overexpression of lga2 in yeast caused no detectable effects. Biochemical analysis has implied that a main portion of Lga2 is tightly associated with mitochondria. Proteomic analysis revealed numerous deregulated proteins in response to lga2 induction, including proteins of the respiratory chain complexes and the TCA cycle. Based on the outer membrane localization of Lga2, however, this likely represents an indirect effect to compensate for a lowered metabolic state. Together with analysis of a role of mitophagy in UPI, this study has strengthened a working model in which Lga2 interferes with mtDNA maintenance and consequently mtRNA levels, which in turn provokes a compensatory response involving Mrb1 to promote translational efficiency. In summary, this work has strongly sharpened ongoing research directions to gain understanding of complex regulatory processes underlying UPI. A surprising result was the finding of enhanced levels as well as of putative isoforms of Mrb1 under lga2-inducing conditions. This may refer to the importance of Mrb1 as central component in controlling mt homeostasis in response to mt dysfunction. In addition, it was surprising that protein levels associated with respiratory chain complexes were differently affected under lga2-imposed stress conditions, suggesting a highly dynamic behaviour in the assembly of their subunits. Furthermore, the robustness of the mt inner membrane of isolated U. maydis mitochondria to the applied detergents was unexpected. The reason for this is currently unknown as analysis of the composition of mt membranes from U. maydis has not yet been studied.
Publications
- (2015) Uniparental mitochondrial DNA inheritance is not affected in Ustilago maydis ∆atg11 mutants blocked in mitophagy. BMC Microbiol. Feb 6;15(1):23
Wagner-Vogel G, Lämmer F, Kämper J, Basse CW
(See online at https://doi.org/10.1186/s12866-015-0358-z)
