The evolutionarily diverged single-stranded DNA-binding proteins SSB1/SSB2 differentially affect the replication, recombination and mutation of organellar genomes in .

Single-stranded DNA-binding proteins (SSBs) play essential roles in the replication, recombination and repair processes of organellar DNA molecules. In , SSBs are encoded by a small family of two genes ( and ). However, the functional divergence of these two copies in plants remains largely unknown, and detailed studies regarding their roles in the replication and recombination of organellar genomes are still incomplete. In this study, phylogenetic, gene structure and protein motif analyses all suggested that SSB1 and SSB2 probably diverged during the early evolution of seed plants. Based on accurate long-read sequencing results, and mutants had decreased copy numbers for both mitochondrial DNA (mtDNA) and plastid DNA (ptDNA), accompanied by a slight increase in structural rearrangements mediated by intermediate-sized repeats in mt genome and small-scale variants in both genomes. Our findings provide an important foundation for further investigating the effects of DNA dosage in the regulation of mutation frequencies in plant organellar genomes.