title: Multiple evolutionary origins of prochlorophytes, the chlorophyll b-containing prokaryotes.
abstract: Prochlorophytes are prokaryotes that carry out oxygenic photosynthesis using chlorophylls a and b, but lack phycobiliproteins as light-harvesting pigments. These characteristics distinguish them from cyanobacteria, which contain phycobiliproteins, but no chlorophyll b. Three prochlorophyte genera have been described: Prochloron, Prochlorothrix and Prochlorococcus. The prochlorophytes share their pigment characteristics with green plant and euglenoid chloroplasts, which has led to a debate on whether these chloroplasts may have arisen from an endosymbiotic prochlorophyte rather than a cyanobacterium. Molecular sequence data, including those presented here based on a fragment of the rpoC1 gene encoding a subunit of DNA-dependent RNA polymerase, indicate that the known prochlorophyte lineages do not include the direct ancestor of chloroplasts. We also show that the prochlorophytes are a highly diverged polyphyletic group. Thus the use of chlorophyll b as a light-harvesting pigment has developed independently several times in evolution. Similar conclusions have been reached in parallel studies using 16S ribosomal RNA sequences.
authors.affiliation: Molecular Genetics and Cell Biology, University of Chicago, Illinois 60637.
authors.forename: B
authors.initials: B
authors.lastname: Palenik
authors.forename: R
authors.initials: R
authors.lastname: Haselkorn
mesh_terms: D000595:Amino Acid Sequence; D017033:Anabaena / Q000235:genetics; D005075:Biological Evolution; D002734:Chlorophyll / Q000378:metabolism*; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000201:enzymology / Q000235:genetics*; D012321:DNA-Directed RNA Polymerases / Q000235:genetics*; D008969:Molecular Sequence Data; D010788:Photosynthesis; D010802:Phylogeny; D010944:Plants / Q000201:enzymology / Q000235:genetics; D016133:Polymerase Chain Reaction; D012689:Sequence Homology, Nucleic Acid
chemical_list: D002734:Chlorophyll; C037184:chlorophyll b; D012321:DNA-Directed RNA Polymerases