title: Biogenesis of photosynthetic complexes in the chloroplast of Chlamydomonas reinhardtii requires ARSA1, a homolog of prokaryotic arsenite transporter and eukaryotic TRC40 for guided entry of tail-anchored proteins.
abstract: as1, for antenna size mutant 1, was obtained by insertion mutagenesis of the unicellular green alga Chlamydomonas reinhardtii. This strain has a low chlorophyll content, 8% with respect to the wild type, and displays a general reduction in thylakoid polypeptides. The mutant was found to carry an insertion into a homologous gene, prokaryotic arsenite transporter (ARSA), whose yeast and mammal counterparts were found to be involved in the targeting of tail-anchored (TA) proteins to cytosol-exposed membranes, essential for several cellular functions. Here we present the characterization in a photosynthetic organism of an insertion mutant in an ARSA-homolog gene. The ARSA1 protein was found to be localized in the cytosol, and yet its absence in as1 leads to a small chloroplast and a strongly decreased chlorophyll content per cell. ARSA1 appears to be required for optimal biogenesis of photosynthetic complexes because of its involvement in the accumulation of TOC34, an essential component of the outer chloroplast membrane translocon (TOC) complex, which, in turn, catalyzes the import of nucleus-encoded precursor polypeptides into the chloroplast. Remarkably, the effect of the mutation appears to be restricted to biogenesis of chlorophyll-binding polypeptides and is not compensated by the other ARSA homolog encoded by the C. reinhardtii genome, implying a non-redundant function.
authors.affiliation: Dipartimento di Biotecnologie, Università di Verona, 15, Strada Le Grazie, I-37134 Verona, Italy.
authors.forename: Cinzia
authors.initials: C
authors.lastname: Formighieri
authors.forename: Stefano
authors.initials: S
authors.lastname: Cazzaniga
authors.forename: Richard
authors.initials: R
authors.lastname: Kuras
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
mesh_terms: D020418:Algal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018053:Arsenites / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D002874:Chromosome Mapping; D003600:Cytosol / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D016254:Mutagenesis, Insertional; D009154:Mutation; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011994:Recombinant Proteins; D017422:Sequence Analysis, DNA
chemical_list: D020418:Algal Proteins; D018053:Arsenites; D008565:Membrane Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins; D011994:Recombinant Proteins; C112475:Toc34 protein, plant; C021261:thylakoid polypeptides; D002734:Chlorophyll; C015001:arsenite