Chloroplast DNA differences between cultivated hop, Humulus lupulus and the related species H. japonicus

Chloroplast DNA (cpDNA) of Humulus Lupulus and H. japonicus was examined by restriction endonuclease analysis with BamHI, BanI, BclI, BstEII, DraI, EcoRI, EcoRV, HindIII, KpnI, PaeR7I, PstI, PvuII, SalI and XhoI. The restriction fragment patterns showed that the cpDNAs shared a large number of restriction sites. However, the chloroplast genomes of the two species could be distinguished by differences in restriction site and restriction fragment patterns in the PstI, PvuII, BclI, EcoRV, DraI and HindIII digests. On the basis of the complexity of restriction enzyme patterns, the enzymes PstI, PvuII, SalI, KpnI and XhoI were selected for mapping the chloroplast genomes. Single and double restriction enzyme digests of cpDNA from the two species were hybridized to cpDNA probes of barley and tobacco. The data obtained from molecular hybridization experiments were used to construct the cleavage site maps. Except for the PstI digest, the arrangement of cpDNA restriction sites was found to be the same for both species. An extra PstI site was present in H. lupulus. Three small insertions/deletions of about 0.8 kbp each were detected in the chloroplast genomes of the two species. Two of these insertions/deletions were present in the large and one in the small singlecopy region of the chloroplast genome. The cpDNA of Humulus was found to be a circular molecule of approximately 148 kbp that contains two inverted repeat regions of 23 kbp each, a small and a large single -copy region of approximately 20 kbp and 81 kbp, respectively. The chloroplast genome of hop has the same physical and structural organization as that found in most angiosperms.