MSH1 is required for maintenance of the low mutation rates in plant mitochondrial and plastid genomes

Significance Plant mitochondrial and plastid genomes maintain unusually low mutation rates, but the mechanisms responsible for their accurate transmission of DNA sequences have remained mysterious. Application of high-fidelity DNA sequencing techniques enabled detection of new mutations still present at low frequencies within tissue samples from the flowering plant Arabidopsis and showed that disrupting a gene in the mutS mismatch repair family ( MSH1 ) increases the frequency of mitochondrial and plastid sequence variants approximately 10-fold to 1,000-fold. This gene has an unusually disjunct distribution across the tree of life, implying a history of horizontal gene transfer among eukaryotes, prokaryotes, and viruses. Its presence in plants and absence in lineages such as animals may contribute to radical differences in organelle mutation rates across eukaryotes.