Avoiding organelle mutational meltdown across eukaryotes with or without a germline bottleneck.

Area of Science:

• Genetics
• Molecular Biology
• Evolutionary Biology

Background:

• Mitochondrial DNA (mtDNA) and plastid DNA (ptDNA) are crucial for cellular energy production.
• Mutations in organelle DNA (oDNA) can lead to severe cellular dysfunction.
• The animal germline bottleneck enhances selection against mutant mtDNA, but its mechanisms and broader eukaryotic relevance are unclear.

Purpose of the Study:

• To develop a comprehensive genetic model explaining how eukaryotes avoid the accumulation of deleterious oDNA mutations (Muller's ratchet).
• To quantitatively describe mechanisms that segregate and reduce oDNA damage across diverse eukaryotic taxa.
• To investigate the role of gene conversion in maintaining oDNA integrity.

Main Methods:

• Development of a predictive genetic model for oDNA mutation dynamics.
• Application of the model to analyze single-cell observations in mouse models.
• Analysis of genomic, transcriptomic, and structural datasets across eukaryotes.

Main Results:

• The animal germline bottleneck was characterized using single-cell data and the developed genetic model.
• Gene conversion was identified as a potent mechanism for increasing beneficial cell-to-cell variance in oDNA without reducing oDNA copy number.
• Evidence supports gene conversion as a key mechanism for managing oDNA damage in organisms lacking a germline bottleneck, including plants and fungi.

Conclusions:

• A unified framework explains how diverse eukaryotes avoid Muller's ratchet, reconciling differences in oDNA management strategies.
• Gene conversion provides a mechanism for generating beneficial genetic variance in oDNA, crucial for organisms without specialized germlines.
• The study clarifies the evolutionary strategies employed by eukaryotes to maintain the integrity of their essential organelle genomes.