ROLLING-CIRCLE REPLICATION OF MITOCHONDRIAL-DNA IN THE HIGHER-PLANT CHENOPODIUM-ALBUM (L)

The mitochondrial genomes of higher plants are larger and more complex than those of all other groups of organisms, We have studied the in v ivo replication of chromosomal and plasmid mitochondrial DNAs prepared from a suspension culture and whole plants of the dicotyledonous high er plant Chenopodium album (L.), Electron microscopic studies revealed sigma-shaped, linear, and open circular molecules (subgenomic circles ) of variable size as well as a minicircular plasmid of 1.3 kb (mp1). The distribution of single-stranded mitochondrial DNA in the sigma str uctures and the detection of entirely single-stranded molecules indica te a rolling-circle type of replication of plasmid mp1 and subgenomic circles, About half of the sigma-like molecules had tails exceeding th e lengths of the corresponding circle, suggesting the formation of con catemers. Two replication origins (nicking sites) could be identified on mp1 by electron microscopy and by a new approach based on the mappi ng of restriction fragments representing the identical 5' ends of the tails of sigma-like molecules. These data provide, for the first time, evidence for a rolling-circle mode of replication in the mitochondria of higher plants.