Molecular Evidence for the Early Evolution of Photosynthesis
Jin Xiong,1
William M. Fischer,1
Kazuhito Inoue,2
Masaaki Nakahara,2
Carl E. Bauer1*
The origin and evolution of photosynthesis have
long remained enigmatic due to a lack of sequence information of
photosynthesis genes across the entire photosynthetic domain. To probe
early evolutionary history of photosynthesis, we obtained new sequence information of a number of photosynthesis genes from the green sulfur
bacterium Chlorobium tepidum and the green nonsulfur
bacterium Chloroflexus aurantiacus. A total of 31 open
reading frames that encode enzymes involved in
bacteriochlorophyll/porphyrin biosynthesis, carotenoid biosynthesis,
and photosynthetic electron transfer were identified in about 100 kilobase pairs of genomic sequence. Phylogenetic analyses of multiple
magnesium-tetrapyrrole biosynthesis genes using a combination of
distance, maximum parsimony, and maximum likelihood methods indicate
that heliobacteria are closest to the last common ancestor of all
oxygenic photosynthetic lineages and that green sulfur bacteria and
green nonsulfur bacteria are each other's closest relatives. Parsimony
and distance analyses further identify purple bacteria as the earliest
emerging photosynthetic lineage. These results challenge previous
conclusions based on 16S ribosomal RNA and Hsp60/Hsp70
analyses that green nonsulfur bacteria or heliobacteria are the
earliest phototrophs. The overall consensus of our phylogenetic
analysis, that bacteriochlorophyll biosynthesis evolved before
chlorophyll biosynthesis, also argues against the long-held Granick
hypothesis.
1 Department of Biology, Indiana University,
Bloomington, IN 47405, USA.
2 Department of
Biological Sciences, Kanagawa University, Hiratsuka, Kanagawa,
259-1293, Japan.
*
To whom correspondence should be addressed. E-mail:
cbauer{at}bio.indiana.edu
