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Presentation
Diatom plastids depend on nucleotide import from the cytosol
Proceedings of the National Academy of Sciences of the United States of America (2009)
  • Michelle Ast, Technische Universität Kaiserslautern
  • Ansgar Gruber, Universität Konstanz
  • Stephan Schmitz-Esser, University of Vienna
  • Horst E. Neuhaus, Technische Universität Kaiserslautern
  • Peter G. Kroth, Universität Konstanz
  • Matthias Horn, University of Vienna
  • Ilka Haferkamp, Technische Universität Kaiserslautern
Abstract
Diatoms are ecologically important algae that acquired their plastids by secondary endosymbiosis, resulting in a more complex cell structure and an altered distribution of metabolic pathways when compared with organisms with primary plastids. Diatom plastids are surrounded by 4 membranes; the outermost membrane is continuous with the endoplasmic reticulum. Genome analyses suggest that nucleotide biosynthesis is, in contrast to higher plants, not located in the plastid, but in the cytosol. As a consequence, nucleotides have to be imported into the organelle. However, the mechanism of nucleotide entry into the complex plastid is unknown. We identified a high number of putative nucleotide transporters (NTTs) in the diatoms Thalassiosira pseudonana and Phaeodactylum tricornutum and characterized the first 2 isoforms (NTT1 and NTT2). GFP-based localization studies revealed that both investigated NTTs are targeted to the plastid membranes, and that NTT1 most likely enters the innermost plastid envelope via the stroma. Heterologously expressed NTT1 acts as a proton-dependent adenine nucleotide importer, whereas NTT2 facilitates the counter exchange of (deoxy-)nucleoside triphosphates. Therefore, these transporters functionally resemble NTTs from obligate intracellular bacteria with an impaired nucleotide metabolism rather than ATP/ADP exchanging NTTs from primary plastids. We suggest that diatoms harbor a specifically-adapted nucleotide transport system and that NTTs are the key players in nucleotide supply to the complex plastid.
Keywords
  • chloroplast,
  • complex plastids,
  • nucleotide synthesis,
  • nucleotide transport
Publication Date
March, 2009
DOI
10.1073/pnas.0808862106
Comments
2009 Ast et al.
Citation Information
Michelle Ast, Ansgar Gruber, Stephan Schmitz-Esser, Horst E. Neuhaus, et al.. "Diatom plastids depend on nucleotide import from the cytosol" Proceedings of the National Academy of Sciences of the United States of America (2009)
Available at: http://works.bepress.com/stephan-schmitz-esser/19/