title: Plastid proteome assembly without Toc159: photosynthetic protein import and accumulation of N-acetylated plastid precursor proteins.
abstract: Import of nuclear-encoded precursor proteins from the cytosol is an essential step in chloroplast biogenesis that is mediated by protein translocon complexes at the inner and outer envelope membrane (TOC). Toc159 is thought to be the main receptor for photosynthetic proteins, but lacking a large-scale systems approach, this hypothesis has only been tested for a handful of photosynthetic and nonphotosynthetic proteins. To assess Toc159 precursor specificity, we quantitatively analyzed the accumulation of plastid proteins in two mutant lines deficient in this receptor. Parallel genome-wide transcript profiling allowed us to discern the consequences of impaired protein import from systemic transcriptional responses that contribute to the loss of photosynthetic capacity. On this basis, we defined putative Toc159-independent and Toc159-dependent precursor proteins. Many photosynthetic proteins accumulate in Toc159-deficient plastids, and, surprisingly, several distinct metabolic pathways are negatively affected by Toc159 depletion. Lack of Toc159 furthermore affects several proteins that accumulate as unprocessed N-acetylated precursor proteins outside of plastids. Together, our data show an unexpected client protein promiscuity of Toc159 that requires a far more differentiated view of Toc159 receptor function and regulation of plastid protein import, in which cytosolic Met removal followed by N-terminal acetylation of precursors emerges as an additional regulatory step.
authors: Department of Biology, Eidgenössische Technische Hochschule Zurich, 8092 Zurich, Switzerland.
authors: Sylvain
authors: S
authors: Bischof
authors: Katja
authors: K
authors: Baerenfaller
authors: Thomas
authors: T
authors: Wildhaber
authors: Raphael
authors: R
authors: Troesch
authors: Pierre-Alexandre
authors: PA
authors: Vidi
authors: Bernd
authors: B
authors: Roschitzki
authors: Matthias
authors: M
authors: Hirsch-Hoffmann
authors: Lars
authors: L
authors: Hennig
authors: Felix
authors: F
authors: Kessler
authors: Wilhelm
authors: W
authors: Gruissem
authors: Sacha
authors: S
authors: Baginsky
mesh_terms: D000107:Acetylation; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D060365:Chloroplast Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D015536:Down-Regulation; D020558:GTP Phosphohydrolases / Q000235:genetics* / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010788:Photosynthesis; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D018087:Plastids / Q000235:genetics / Q000378:metabolism*; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; D008565:Membrane Proteins; D011498:Protein Precursors; C403444:TOC159 protein, Arabidopsis; D008715:Methionine; D020558:GTP Phosphohydrolases