Plant and Cell Physiology Advance Access originally published online on October 27, 2006
Plant and Cell Physiology 2006 47(12):1622-1629; doi:10.1093/pcp/pcl026
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Identification of Chlorophyllide a Oxygenase in the Prochlorococcus Genome by a Comparative Genomic Approach
1 Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, 060-0810 Japan
2 Institute of Low Temperature Science, Hokkaido University, Sapporo, 060-0819 Japan
* Corresponding author: E-mail, Ayumi{at}pop.lowtem.hokudai.ac.jp; Fax, +81-11-706-5493.
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Abstract |
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Chl b is a major photosynthetic pigment of peripheral antenna complexes in chlorophytes and prochlorophytes. Chl b is synthesized by chlorophyllide a oxygenase (CAO), an enzyme that has been identified from higher plants, moss, green algae and two groups of prochlorophytes, Prochlorothrix and Prochloron. Based on these results, we previously proposed the hypothesis that all of the Chl b synthesis genes have a common origin. However, the CAO gene is not found in whole genome sequences of Prochlorococcus although a gene which is distantly related to CAO was reported. If Prochlorococcus employs a different enzyme, a Chl synthesis gene should have evolved several times on the different phylogenetic lineages of Prochlorococcus and other Chl b-containing organisms. To examine these hypotheses, we identified a Prochlorococcus Chl b synthesis gene by using a combination of bioinformatics and molecular genetics techniques. We first identified Prochlorococcus-specific genes by comparing the whole genome sequences of Prochlorococcus marinus MED4, MIT9313 and SS120 with Synechococcus sp. WH8102. Synechococcus is closely related to Prochlorococcus phylogenetically, but it does not contain a Chl b synthesis gene. By examining the sequences of Prochlorococcus-specific genes, we found a candidate for the Chl b synthesis gene and introduced it into Synechocystis sp. PCC6803. The transformant cells accumulated Chl b, indicating that the gene product catalyzes Chl b synthesis. In this study, we discuss the evolution of CAO based upon the molecular phylogenetic studies we performed.
Keywords: BLAST - Chlorophyll - Chlorophyllide a oxygenase - Comparative genomics - Prochlorococcus
Abbreviations: CAO, chlorophyllide a oxygenase; DVR, 3, 8-divinyl protochlorophyllide 8-vinyl reductase; ORF, open reading frame; PcCAO, Prochlorococcus CAO.
(Received September 7, 2006; Accepted October 20, 2006)
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