Physical and gene mapping of chloroplast DNA from normal and cytoplasmic male sterile (radish cytoplasm) lines of Brassica napus.

Using the restriction endonucleases SaII, SmaI, BgII and KpnI, physical maps of chloroplast DNA isolated from normal and cytoplasmic male sterile (radish cytoplasm) lines of B. napus were constructed and compared. In this study, a rapid and simple procedure was developed for the isolation of chloroplast DNA restriction fragments from low gelling temperature agarose gels.The overall structural organization of N and cms B. napus appears to be rather similar to that of cpDNAs of other higher plants. It is composed of two identical sequences (each about 15 Md) arranged as an inverted repeat separated by two single copy-regions of different sizes (about 54 and 15 Md). In both genomes the ribosomal RNAs are encoded by duplicate genes situated at one end of the inverted repeat. The two chloroplast genomes are distinguished by a point mutation in the rRNA locus. Genes for the large subunit of ribulose-1.5-biphosphate carboxylase and a 32 kilodalton photosystem II polypeptide are separated by a minimum of 30 Md of DNA within the large single copy region.