MSH1 maintains organelle genome stability and genetically interacts with RECA and RECG in the moss Physcomitrella patens. (1st June 2017) - Odahara, Masaki
Summary: Chloroplast and mitochondrial DNA encodes genes that are essential for photosynthesis and respiration, respectively. Thus, loss of integrity of the genomic DNA of organelles leads to a decline in organelle function and alteration of organelle genetic information. RECA (RECA1 and RECA2) and RECG, which are homologs of bacterial homologous recombination repair (HRR) factors RecA and RecG, respectively, play an important role in the maintenance of integrity of the organelle genome by suppressing aberrant recombination between short dispersed repeats (SDRs) in the moss Physcomitrella patens . On the other hand, MutS homolog 1 (MSH1), a plant‐specific MSH with a C‐terminal GIY‐YIG endonuclease domain, is involved in the maintenance of integrity of the organelle genome in the angiosperm Arabidopsis thaliana . Here, we address the role of the duplicated MSH1 genes, MSH1A and MSH1B, in P. patens, in which MSH1A lacks the C‐terminal endonuclease domain. MSH1A and MSH1B localized to both chloroplast and mitochondrial nucleoids in protoplast cells. Single and double knockout (KO) mutants of MSH1A and MSH1B showed no obvious morphological defects; however, MSH1B KO and double KO mutants, as well as MSH1B GIY‐YIG deletion mutants, exhibited genomic instability due to recombination between SDRs in chloroplasts and mitochondria. Creating double KO mutations of each combination of MSH1B, RECA2 and RECG synergistically increased recombination between SDRs in chloroplasts and mitochondria. These results show the role of MSH1 in the maintenance of integrity of the organelle genome and the genetic interaction between MSH1 and homologs of HRR factors in the basal land plant P. patens . Significance Statement: Maintenance of stability of the chloroplast and mitochondrial genomes is essential for photosynthesis and respiration, respectively, and MSH1 is known to be involved in maintenance of the genome stability of organelles in angiosperms. However, the role of MSH1 in chloroplasts remains poorly characterized. Here, we find that MSH1 suppresses recombination between short dispersed repeats in organellar genomes in Physcomitrella patens, and genetically interacts with homologs of genes for bacterial homologous recombination, RECA and RECG, to maintain the genome stability of organelles.