Horizontally transferred mitochondrial DNA tracts become circular by microhomology-mediated repair pathways

Area of Science:

• Plant genomics
• Mitochondrial genetics
• Horizontal gene transfer

Background:

• The holoparasitic plant Lophophytum mirabile shows extensive mitochondrial horizontal gene transfer (HGT).
• Understanding HGT mechanisms requires comparative data from related species and their hosts.

Purpose of the Study:

• To investigate the origin and timing of mitochondrial HGT in Lophophytum species.
• To elucidate the molecular mechanisms driving extensive HGT in plant mitochondria.
• To propose a novel model for mitochondrial HGT.

Main Methods:

• Sequencing of mitochondrial genomes (mtDNA) from Lophophytum species and mimosoid hosts.
• Application of stringent phylogenomic analyses to trace gene origins.
• Investigation of DNA repair pathways involved in foreign DNA integration.

Main Results:

• Ancestral and recent HGT events significantly altered Lophophytum spp. mtDNA, with foreign DNA comprising up to 74%.
• Fourteen foreign mitochondrial chromosomes originated from host mtDNA, flanked by direct repeats and circularized.
• Foreign noncoding chromosomes exist independently and are subject to genetic drift.

Conclusions:

• A novel 'circle-mediated HGT' model is proposed, where foreign DNA forms independent, plasmid-like circular molecules.
• This model suggests successful HGT does not require integration into the recipient genome.
• The findings challenge conventional understanding of gene transfer mechanisms in eukaryotes.