Msh1

Maréchal A & Brisson N 2010 Recombination and the maintenance of plant organelle genome stability. New Phytol 186:299-317.

  • there are apparently no plant MutL or MutH homologues predicted to localize to organelles
  • this protein represents a compact system with mismatch recognition and endonuclease functions bundled together
  • the role of MutS family proteins in preventing recombination between homeologous DNA regions is broadly conserved in bacteria, yeast, humans and plants
  • MSH1 proteins from Arabidopsis and tomato can localize to both organelles whereas their counterparts from maize and soybean (Glycine max) are targeted solely to mitochondria
  • As no plastid DNA rearrangements have been observed to date in msh1 mutants, it is possible that MSH1 proteins could play additional roles in the plastids of some plant species
  • very few genes of the RecA family have been found outside prokaryotes
  • the discovery of a RecA homologue encoding a protein that localizes to the stroma of pea (Pisum sativum) chloroplasts was thus somewhat surprising
  • complete sequencing of the nuclear genome of Arabidopsis revealed that it harbours at least three active RecA homologues
  • a fourth RecA-like gene exists but as it encodes a heavily truncated protein, it is probably a pseudogene
  • the effect of RecA3 mutation on mtDNA recombination is different from that observed in msh1 plants
  • the affected repeats appear to be a subset of those perturbed in MSH1 mutant plants
  • reintroducing a functional copy of RecA3 can result in the loss of aberrant DNA molecules in the majority of the progeny
  • recA3 single mutants have no phenotype that could distinguish them from WT plants, indicating that mitochondria can cope with a certain level of rearrangements
  • the other two RecA homologues are apparently essential for viability as null alleles could not be recovered
  • the RecA3 protein differs from RecA1 and RecA2 in that it lacks the acidic C-terminal domain also found in prokaryotic RecA proteins
  • C-terminal deletions in bacterial recombinases enhances most in vitro activities of RecA, supporting an autoregulatory role for this portion of the protein
  • the antirecombination activity of MutS is a result of the inhibition of RecA-mediated strand-transfer activity between ssDNA molecules and homeologous or damaged DNA duplexes
  • MSH1 might have a similar regulatory role in the strand-exchange activity of RecA homologues in plant organelles