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

Recent phylogenetic studies suggest that plastid ribosomal RNA genes from Pylaiella littoralis have a cyanobacterial origin, whereas their Rubisco genes are related to the homologous alpha- and beta- purple eubacterial genes. We have constructed a phylogenetic tree based upon the atpB and atpE sequences, including the same range of taxa (chlorophytes, chromophytes, cyanobacteria, alpha- and gamma-purple eubacteria) and 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 hypotheses that could explain the apparently composite origin of red-chromophyte plastomes are discussed.