title: Importance of Translocon Subunit Tic56 for rRNA Processing and Chloroplast Ribosome Assembly.
abstract: Toc159-containing complexes at the outer chloroplast envelope membrane form stable supercomplexes with a 1-MD translocon at the inner chloroplast envelope membrane of which Tic56 is one essential subunit. While the single mutants tic56-1 and ppi2 (toc159) have an albino phenotype and are able to grow heterotrophically, we find the double mutant to be embryo lethal. Comprehensive quantitative proteome profiling with both single mutants in combination with GeneChip analyses identified a posttranscriptional defect in the accumulation of plastid ribosomal proteins and diminished expression of plastid encoded proteins. In the tic56-1 mutant, the assembly of functional ribosomes is furthermore hampered by a processing defect of the plastid 23S rRNA. Spectinomycin-treatment of wild-type plants phenocopies the molecular phenotype of plastid proteome accumulation in tic56-1 and to a smaller degree also ppi2 plastids, suggesting that a defect in plastid translation is largely responsible for the phenotype of both import mutants. Import experiments with the tic56-3 mutant revealed no significant defect in the import of small ribosomal protein 16 in the absence of full-length Tic56, suggesting that the defect in ribosome assembly in tic56-1 may be independent of a function of Tic56 in protein import. Our data establish a previously unknown link between plastid protein import, the processing of plastid rRNAs, and the assembly of plastid ribosomes and provide further knowledge on the function of the translocon components and the molecular basis for their albino phenotype.
authors.affiliation: Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, Biozentrum, 06120 Halle (Saale), Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Köhler
authors.affiliation: Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, Biozentrum, 06120 Halle (Saale), Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Helm
authors.affiliation: Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, Biozentrum, 06120 Halle (Saale), Germany.
authors.forename: Birgit
authors.initials: B
authors.lastname: Agne
authors.affiliation: Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, Biozentrum, 06120 Halle (Saale), Germany sacha.baginsky@biochemtech.uni-halle.de.
authors.forename: Sacha
authors.identifier: 0000-0002-5440-3898
authors.initials: S
authors.lastname: Baginsky
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D060365:Chloroplast Proteins / Q000378:metabolism; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D014176:Protein Biosynthesis / Q000187:drug effects; D021122:Protein Subunits / Q000378:metabolism*; D020543:Proteome / Q000378:metabolism; D040901:Proteomics; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects / Q000235:genetics*; D012335:RNA, Ribosomal / Q000235:genetics* / Q000378:metabolism; D012269:Ribosomal Proteins / Q000378:metabolism; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism*; D012639:Seeds / Q000187:drug effects / Q000378:metabolism; D000198:Spectinomycin / Q000494:pharmacology
chemical_list: D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; D026901:Membrane Transport Proteins; D021122:Protein Subunits; D020543:Proteome; D012335:RNA, Ribosomal; D012269:Ribosomal Proteins; C000604211:Tic56 protein, Arabidopsis; D000198:Spectinomycin