Preferential amplification of mitochondrial DNA fragments in somatic hybrids of the Gramineae

Summary

Somatic hybrid cell lines of Pennisetum americanum + Panicum maximum, and of Pennisetum americanum + Saccharum officinarum display unique mitochondrial DNA (mtDNA) restriction patterns suggestive of mitochondrial fusion and recombination. Apparent recombinant fragments of the hybrids were recovered, cloned, and hybridized to parental and somatic hybrid mtDNAs. In each somatic hybrid, “novel” fragments were found to be present at low copy number in one or both of the parental mtDNAs, and amplified 15–30 times in the hybrids. In pearl millet-sugarcane somatic hybrid cells, the amplification does not appear to involve enhanced recombination. The presumably amplified restriction fragment of the pearl millet-Guinea grass somatic hybrids is a junction fragment of a repeat, present in low copy number in both parents, and in high copy number in the hybrids. Thus protoplast and probable mitochondrial fusion results in a marked shift in the direction of mtDNA recombination events. We conclude that amplification of parental mtDNA fragments is a common event in somatic hybrid cells of these Gramineae.