, Volume 58, Issue 1–3, pp 127–133 | Cite as

Conservative sorting in the muroplasts of Cyanophora paradoxa: a reevaluation based on the completed genome sequence

  • Jürgen M. Steiner
  • Debashish Bhattacharya
  • Wolfgang Löffelhardt


After primary endosymbiosis, massive gene transfer occurred from the genome of the cyanobacterial endosymbiont to the nucleus of the protist host cell. In parallel, a specific protein import apparatus arose for reimport of many, but not all products of the genes moved to the nuclear genome. Presequences evolved to allow recognition of plastid proteins at the envelope and their translocation to the stroma. However, plastids (and cyanobacteria) also comprise five other subcompartments. Protein sorting to the cyanobacterial thylakoid membrane, the thylakoid lumen, the inner envelope membrane, the periplasmic space, and the outer envelope membrane is achieved by prokaryotic protein translocases recognizing, e.g., signal sequences. The “conservative sorting” hypothesis postulates that these translocases remained functional in endosymbiotic organelles and obtained their passengers not only from imported proteins but also from proteins synthesized in organello. For proteins synthesized in the cytosol, a collaboration of the general import apparatus and the former prokaryotic translocase is necessary which is often reflected by the use of bipartite presequences, e.g., stroma targeting peptide and signal peptide. For plants, this concept has been experimentally proven and verified. The muroplasts from Cyanophora paradoxa, that have several features more in common with cyanobacteria than with plastids, were analyzed with the availability of the recently completed nuclear genome sequence. Interesting findings include the absence of the post-translational signal recognition particle pathway, dual Sec translocases in thylakoid and inner envelope membranes that are produced from a single set of genes, and a co-translational signal recognition pathway operating without a 4.5S RNA component.


Cyanophora paradoxa Glaucophyta Muroplasts Conservative sorting 



Support from the “Fonds zur Förderung der wissenschaftlichen Forschung” (P19683, to W.L.) is gratefully acknowledged. We are indebted to M.A. Rosenblad (Gothenburg) for communicating data prior to publication.


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Copyright information

© Springer Science+Business Media Dordrecht 2012

Authors and Affiliations

  • Jürgen M. Steiner
    • 1
  • Debashish Bhattacharya
    • 2
  • Wolfgang Löffelhardt
    • 3
  1. 1.Department of Biology/Plant PhysiologyMartin-Luther-University Halle-WittenbergHalleGermany
  2. 2.Department of Ecology, Evolution, and Natural Resources and Institute of Marine and Coastal SciencesRutgers UniversityNew BrunswickUSA
  3. 3.Max F. Perutz Laboratories, Department of Biochemistry and Cell BiologyUniversity of ViennaViennaAustria

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