Amplification of Nicotiana sylvestris mitochondrial subgenomes is under nuclear control and is associated with phenotypic changes.

We have previously shown the presence in a Nicotiana sylvestris protoplast-derived plant of both a nuclear mutation conferring male sterility (ms4) and a mtDNA reorganisation, named U, characterised by the amplification of substoichiometric mtDNA fragments generated by recombination in the parent T mtDNA. Here we show by physical mapping that the recombining repeats are in direct orientation, thus generating two subgenomes both of which are amplified in the U organisation to the detriment of the parent molecule, and are maintained through sexual reproduction. The nuclear ms4 mutation is likely to have play a role in the shift in mitochondrial molecule equilibrium, as higher levels of recombinant fragments were present in protoplast-derived T calli carrying the ms4 allele than in wild type calli or leaves.