How do endosymbionts become organelles? Understanding early events in plastid evolution

Authors

  • Debashish Bhattacharya,

    Corresponding author
    1. Department of Biological Sciences and the Roy J. Carver Center for Comparative Genomics, University of Iowa, Iowa City.
    • University of Iowa, Department of Biological Sciences and the Roy J. Carver Center for Comparative Genomics, 446 Biology Building, Iowa City, IA 52242.
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  • John M. Archibald,

    1. The Canadian Institute for Advanced Research, Program in Evolutionary Biology, Department of Biochemistry and Molecular Biology, Dalhousie University, Sir Charles Tupper Medical Building, Halifax, Nova Scotia, Canada.
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  • Andreas P.M. Weber,

    1. Department of Plant Biochemistry, Heinrich-Heine-University, 40225 Düsseldorf, Germany
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  • Adrian Reyes-Prieto

    1. Department of Biological Sciences and the Roy J. Carver Center for Comparative Genomics, University of Iowa, Iowa City.
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Abstract

What factors drove the transformation of the cyanobacterial progenitor of plastids (e.g. chloroplasts) from endosymbiont to bona fide organelle? This question lies at the heart of organelle genesis because, whereas intracellular endosymbionts are widespread in both unicellular and multicellular eukaryotes (e.g. rhizobial bacteria, Chlorella cells in ciliates, Buchnera in aphids), only two canonical eukaryotic organelles of endosymbiotic origin are recognized, the plastids of algae and plants and the mitochondrion. Emerging data on (1) the discovery of non-canonical plastid protein targeting, (2) the recent origin of a cyanobacterial-derived organelle in the filose amoeba Paulinella chromatophora, and (3) the extraordinarily reduced genomes of psyllid bacterial endosymbionts begin to blur the distinction between endosymbiont and organelle. Here we discuss the use of these terms in light of new data in order to highlight the unique aspects of plastids and mitochondria and underscore their central role in eukaryotic evolution. BioEssays 29:1239–1246, 2007. © 2007 Wiley Periodicals, Inc.

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