Mitochondrial fusion increases the mitochondrial DNA copy number in budding yeast

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Mitochondrial fusion is crucial for maintaining mitochondrial DNA (mtDNA), but the exact mechanisms remain elusive.
• Reactive oxygen species (ROS) can stimulate recombination-mediated mtDNA replication in yeast.
• The homologous DNA pairing protein Mhr1 is essential for mtDNA maintenance.

Purpose of the Study:

• To investigate the role of mitochondrial fusion in mtDNA maintenance.
• To elucidate the mechanisms by which mitochondrial fusion influences mtDNA copy number.
• To explore the involvement of ROS and specific proteases in this process.

Main Methods:

• Monitoring yeast mitochondrial fusion using bimolecular fluorescence complementation (BiFC) with green fluorescent protein (GFP).
• Assessing mtDNA copy number changes in wild-type and mutant yeast strains.
• Analyzing the impact of reactive oxygen species (ROS) levels and inner membrane AAA proteases (e.g., Yme1) on mtDNA synthesis and maintenance.

Main Results:

• Mitochondrial fusion increases mtDNA copy number in an Mhr1-dependent manner.
• Fusion events lead to increased ROS levels, associated with the degradation of electron transport chain complex IV subunits by Yme1.
• Elevated ROS levels enhance de novo mtDNA synthesis and copy number, while reducing ROS in yme1 mutants decreases mtDNA copy number, increasing mtDNA-less cells.

Conclusions:

• Mitochondrial fusion induces mtDNA synthesis through ROS-triggered, recombination-mediated replication.
• This fusion-dependent mechanism is critical for preventing the formation of mtDNA-lacking mitochondria.
• The interplay between mitochondrial fusion, ROS, and proteases like Yme1 is vital for robust mtDNA maintenance.