Variant mitochondrial plasmids of broad bean arose by recombination and are controlled by the nuclear genome

Various cytoplasms of broad bean contain three mitochondrial plasmids (mtp1, 2 and 3), previously described. In cytoplasm 350 we have observed several additional mitochondrial plasmids, varying in number and in identity according to the nuclear background. Replacement of the nucleus by backcrossing led to the appearance or disappearance of additional plasmids, indicating that the nuclear genome controls either the creation or the copy level of mitochondrial plasmids. Analysis of eight variant additional plasmids (mtp4-11) suggests that they all result from a double recombination event between mtp1 and mtp2. In all cases, one recombination point was located within a 276-bp sequence, identical in both plasmids. For 7 plasmids, the region in which the second recombination event occurred could be narrowed down to a short stretch containing imperfect tandem repeats of a 31-bp motif. The largest sequence shared by the recombination regions was hexanucleotide GCGACG.