MITOCHONDRIAL-DNA VARIABILITY DETECTED IN A SINGLE WHEAT REGENERANT INVOLVES A RARE RECOMBINATION EVENT ACROSS A SHORT REPEAT

The mitochondrial genome of the selfed progeny of a plant regenerated from long-term somatic tissue culture displays specific structural rea rrangements characterized by the appearance of novel restriction fragm ents. A mitochondrial DNA library was constructed from this selfed pro geny in the SalI site of cosmid pHC79 and the novel fragments were sub sequently studied. They were shown to arise from reciprocal recombinat ion events involving DNA sequences present in the parental plant. The regions of recombination were sequenced and the nucleotide sequences w ere aligned with those of the presumptive parental fragments. We chara cterized an imperfect short repeated DNA sequence, 242 bp long, within which a 7-bp DNA repeat could act as a region of recombination. The u se of PCR technology allowed us to show that these fragments were pres ent in both parental plants and tissue cultures as low-abundance seque nce arrangements.