Molecular Evidence for the Early Evolution of Photosynthesis

Rcjohnsen rcjohnsen at
Mon Sep 11 21:43:48 EST 2000

Sept 8th Sci 1719-1724
Molecular Evidence for the Early Evolution of Photosynthesis 

Jin Xiong,1 William M. Fischer,1 Kazuhito Inoue,2 Masaaki Nakahara,2 Carl E.
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.  

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