Extensive sequence rearrangements in the chloroplast genomes of the green algaeChlamydomonas eugametos andChlamydomonas reinhardtii

Summary We have compared the overall sequence organization of chloroplast DNA (cpDNA) from the unicellular green algaeChlamydomonas eugametos andChlamydomonas reinhardtii. Cloned restriction fragments whose locations are known on the chloroplast genome of one or the other alga were hybridized to Southern blots of cpDNA digests from both algae and the positions of hybridization signals were used to align the two algal cpDNA restriction maps. In agreement with the important biological differences reported betweenC. eugametos andC. reinhardtii, we found extensive sequence rearrangements and low overall sequence homology between the two cpDNAs. To explain the striking contrast between our results and the remarkable conservation reported for the sequence and the organization of angiosperm cpDNAs containing inverted repeats, we suggest that the divergence between theC. eugametos andC. reinhardtii chloroplast genomes simply reflects a longer time of separate evolution relative to the angiosperm lineages. However, we cannot exclude the possibility that the algal cpDNAs rearranged faster than angiosperm cpDNAs.