MOLECULAR PHYLOGENY OF THE ATPB AND ATPE GENES OF THE BROWN ALGA PYLAIELLA-LITTORALIS

Recent phylogenetic studies suggest that plastid ribosomal RNA genes f rom Pylaiella littoralis have a cyanobacterial origin, whereas their R ubisco genes are related to the homologous alpha- and beta- purple eub acterial genes. We have constructed a phylogenetic tree based upon the atpB and atpE sequences, including the same range of taxa (chlorophyt es, chromophytes, cyanobacteria, alpha- and gamma-purple eubacteria) a nd using the same methods as previously described for rbcL genes. This phylogenetic tree clearly shows that the atpB and atpE genes of this brown alga are more closely related to their cyanobacterial homologues than to those of alpha- or gamma-purple eubacteria. Different hypothe ses that could explain the apparently composite origin of red-chromoph yte plastomes are discussed.