Mitochondrial plasmids of Neurospora: integration into mitochondrial DNA and evidence for reverse transcription in...

Area of Science:

• Molecular Biology
• Mycology
• Genetics

Background:

• The Mauriceville and Varkud mitochondrial plasmids in Neurospora are circular DNA molecules.
• Their genetic makeup suggests a link to mobile genetic elements like retrotransposons and introns.

Purpose of the Study:

• To investigate the detrimental effects of these mitochondrial plasmids on Neurospora growth.
• To characterize the molecular basis of plasmid-induced growth impairment.

Main Methods:

• Isolation and characterization of Neurospora mutants exhibiting impaired growth due to plasmid activity.
• Analysis of plasmid and mitochondrial DNA (mtDNA) sequences in mutant strains.
• Investigation of plasmid structure, including insertions and integration sites.

Main Results:

• Twelve mutants with impaired growth were identified, all harboring suppressive variant plasmids.
• Ten of these mutants also showed defective mitochondrial DNA (mtDNA).
• Suppressive plasmids contained insertions, often including tRNA sequences, near the 5' RNA start site, suggesting reverse transcription involvement.
• Mitochondrial plasmid sequences were found integrated into the mtDNA of at least three mutants, with junctions indicative of RNA-mediated integration.

Conclusions:

• The study demonstrates that Neurospora mitochondrial plasmids can exhibit detrimental behavior, leading to impaired growth and defective mtDNA.
• The findings suggest a mechanism involving RNA intermediates and reverse transcription in the generation and integration of these suppressive plasmids.
• These plasmids represent a unique example of mobile genetic elements impacting host mitochondrial genome integrity.