RAP, the Sole Octotricopeptide Repeat Protein in Arabidopsis, Is Required for Chloroplast 16S rRNA Maturation

• Published in: The Plant cell 2014-02, Vol.26 (2), p.777-787
• Main Authors: Kleinknecht, Laura, Wang, Fei, Stube, Roland, Philippar, Katrin, Nickelsen, Jörg, Bohne, Alexandra-Viola
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Arabidopsis - metabolism; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - metabolism; Binding Sites; Chloroplasts; Chloroplasts - metabolism; Conserved Sequence; Gels; Molecular Sequence Data; Mutation - genetics; Plant cells; Plants; Plastids; Protein Binding; Protein Biosynthesis; Proteins; Repetitive Sequences, Amino Acid; Ribosomes; RNA; RNA precursors; RNA Precursors - metabolism; RNA probes; RNA, Plant - metabolism; RNA, Ribosomal, 16S - metabolism; RNA-Binding Proteins - chemistry; RNA-Binding Proteins - metabolism
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.114.122853

The biogenesis and activity of chloroplasts in both vascular plants and algae depends on an intracellular network of nucleusencoded, trans-acting factors that control almost all aspects of organellar gene expression. Most of these regulatory factors belong to the helical repeat protein superfamily, which includes tetratricopeptide repeat, pentatricopeptide repeat, and the recently identified octotricopeptide repeat (OPR) proteins. Whereas green algae express many different OPR proteins, only a single orthologous OPR protein is encoded in the genomes of most land plants. Here, we report the characterization of the only OPR protein in Arabidopsis thaliana, RAP, which has previously been implicated in plant pathogen defense. Loss of RAP led to a severe defect in processing of chloroplast 16S rRNA resulting in impaired chloroplast translation and photosynthesis. In vitro RNA binding and RNase protection assays revealed that RAP has an intrinsic and specific RNA binding capacity, and the RAP binding site was mapped to the 5' region of the 16S rRNA precursor. Nucleoid localization of RAP was shown by transient green fluorescent protein import assays, implicating the nucleoid as the site of chloroplast rRNA processing. Taken together, our data indicate that the single OPR protein in Arabidopsis is important for a basic process of chloroplast biogenesis.