Small interspersed sequences that serve as recombination sites at the cox2 and atp6 loci in the mitochondrial genome of soybean are widely distributed in higher plants

Abstract

Mitochondrial DNA (mtDNA) fragments that contain cox2 and atp6 were cloned from a wild soybean (Glycine soja, accession `B09002') and from a cultivated soybean (G. max, `Harosoy'). Comparison of these DNAs revealed that two sets of repeated sequences, namely, 299 bp and 23 bp, were present in the 5′ regions of cox2 and atp6. The 299-bp and 23-bp repeats were present close to each other on the 5′ flanking region and the 5′ part of the coding region of cox2 in both `Harosoy' and `B09002', as well as on the 5′ flanking region of atp6 in `Harosoy', while these two repeats were separated by a 706-bp nucleotide sequence that contained a truncated sequence of nad3 at the 5′ flanking region of atp6 in `B09002'. The mtDNA configurations upstream from atp6 and cox2 found in `Harosoy' appeared to have been generated from configurations of cox2 and atp6 found in `B09002' via recombination across the 299-bp or 23-bp repeated sequences, or vice versa, in the mitochondrial genome of the hypothetical progenitor of these plants. The 299-bp sequence was found to be interspersed in the mitochondrial genome. Eight loci were identified that include mtDNA configurations that are inter-convertible with each other via recombination across this sequence in `B09002'. Various loci on the mitochondrial genomes of higher plants that harbor segments of the 299-bp repeats in Glycine were identified.