Biogenesis of photosynthetic complexes in the chloroplast of C hlamydomonas reinhardtii requires ARSA 1, a homolog of prokaryotic arsenite transporter and eukaryotic TRC 40 for guided entry of tail‐anchored proteins

• Published in: The Plant journal : for cell and molecular biology 2013-03, Vol.73 (5), p.850-861
• Main Authors: Formighieri, Cinzia, Cazzaniga, Stefano, Kuras, Richard, Bassi, Roberto
• Format: Article
• Language: English
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.12077

as1 , for antenna size mutant 1 , was obtained by insertion mutagenesis of the unicellular green alga C hlamydomonas 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 ARSA 1 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. ARSA 1 appears to be required for optimal biogenesis of photosynthetic complexes because of its involvement in the accumulation of TOC 34, 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.