Variable number of tandem repeat loci in the mitochondrial genomes of beets

We found four unrelated tandem repeat loci (TR1, TR2, TR3 and TR4) in the mitochondrial genomes of beets, with the TR1 locus embedded within a three-membered family of recombining repeat sequences (the rrn26-repeat). TR1 is composed of an array of 32-bp tandem repeats, the number of which varies from 2 to 13 among the seven beet genotypes examined. It is interesting to note that TR1 has 7-bp direct repeats flanking the array, which may be involved in the generation of the tandem repeat array. Such striking features are shared by the remaining TR loci, and this is thus the first description of minisatellite nucleotide sequences from a higher-plant mitochondrial genome.