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Tracking molecular evolution of photosynthesis by characterization of a major photosynthesis gene cluster from Heliobacillus mobilis - PubMed

  • ️Thu Jan 01 1998

Tracking molecular evolution of photosynthesis by characterization of a major photosynthesis gene cluster from Heliobacillus mobilis

J Xiong et al. Proc Natl Acad Sci U S A. 1998.

Abstract

A DNA sequence has been obtained for a 35.6-kb genomic segment from Heliobacillus mobilis that contains a major cluster of photosynthesis genes. A total of 30 ORFs were identified, 20 of which encode enzymes for bacteriochlorophyll and carotenoid biosynthesis, reaction-center (RC) apoprotein, and cytochromes for cyclic electron transport. Donor side electron-transfer components to the RC include a putative RC-associated cytochrome c553 and a unique four-large-subunit cytochrome bc complex consisting of Rieske Fe-S protein (encoded by petC), cytochrome b6 (petB), subunit IV (petD), and a diheme cytochrome c (petX). Phylogenetic analysis of various photosynthesis gene products indicates a consistent grouping of oxygenic lineages that are distinct and descendent from anoxygenic lineages. In addition, H. mobilis was placed as the closest relative to cyanobacteria, which form a monophyletic origin to chloroplast-based photosynthetic lineages. The consensus of the photosynthesis gene trees also indicates that purple bacteria are the earliest emerging photosynthetic lineage. Our analysis also indicates that an ancient gene-duplication event giving rise to the paralogous bchI and bchD genes predates the divergence of all photosynthetic groups. In addition, our analysis of gene duplication of the photosystem I and photosystem II core polypeptides supports a "heterologous fusion model" for the origin and evolution of oxygenic photosynthesis.

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Figures

Figure 1
Figure 1

The H. mobilis photosynthesis gene cluster. Directions of transcription are indicated by thick solid arrows with the plasmid pHM6 insert sequence delineated with a bracket.

Figure 2
Figure 2

Comparison of organizations of pet genes coding for cytochrome bc/bc1/b6f complexes from various organisms. The nuclear-encoded genes are enclosed in dashed lines. Separated boxes indicate nonlinked genes on chromosome.

Figure 3
Figure 3

(A) This phylogenetic tree of BchL/ChlL was created with the neighbor-joining method. NifH from M. jannaschii is used as an outgroup. Photosynthetic taxa are delineated by brackets and identified as oxygenic (+O2) or anoxygenic (−O2). Horizontal branch lengths represent relative evolutionary distances with the scale bar corresponding to 0.1 amino acid substitutions per site. Bootstrap values above 40% are indicated at each node, except basal nodes. (B) This phylogenetic tree of BchH/ChlH used CobN from M. jannaschii as an outgroup. (C) This phylogenetic tree of PetB used PetB from Sulfolobus acidocaldarius as an outgroup. (D) This composite phylogenetic tree of paralogous gene products Mg-chelatase subunits BchI/ChlI/BchD/ChlD used BchI and BchD homolog from Methanobacterium thermoautotrophicum as an outgroup. (C) This composite phylogenetic tree of PSI-like RC polypeptides (PshA/PscA/PsaA/PsaB) together with two PSII core antenna polypeptides (CP47 and CP43) used PscA of C. limicola as an outgroup.

Figure 4
Figure 4

A heterologous fusion model for the evolution of oxygenic photosynthesis based on phylogenetic analysis. Details of the model are provided in the text.

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