Physical map of chloroplast DNA in sugi, Cryptomeria japonica

To investigate the evolution of conifer species, we constructed a physical map of the chloroplast DNA of sugi, Cryptomeria japonica, with four restriction endonucleases, PstI, SalI, SacI and XhoI. The chloroplast genome of C. japonica was found to be a circular molecule with a total size of approximately 133 kb. This molecule lacked an inverted repeat. Twenty genes were localized on the physical map of C. japonica cpDNA by Southern hybridization. The chloroplast genome structure of C. japonica showed considerable rearrangements of the standard genome type found in vascular plants and differed markedly from that of tobacco. The difference was explicable by one deletion and five inversions. The chloroplast genome of C. japonica differed too from that of the genus Pinus which also lacks one of the inverted repeats. The results indicate that the conifer group originated monophyletically from an ancient lineage, and diverged independently after loss of an inverted repeat structure.