Abstract
Post-transcriptional C-to-U RNA editing occurs in plant plastid and mitochondrial transcripts. Members of the Arabidopsis RNA-editing factor interacting protein (RIP) family and ORRM1 (Organelle RNA Recognition Motif-containing protein 1) have been recently characterized as essential components of the chloroplast RNA editing apparatus. ORRM1 belongs to a distinct clade of RNA Recognition Motif (RRM)-containing proteins, most of which are predicted to be organelle-targeted. Here we report the identification of two proteins, ORRM2 (organelle RRM protein 2) and ORRM3 (organelle RRM protein 3), as the first members of the ORRM clade to be identified as mitochondrial editing factors. Transient silencing of ORRM2 and ORRM3 resulted in reduced editing efficiency at ∼6% of the mitochondrial C targets. In addition to an RRM domain at the N terminus, ORRM3 carries a glycine-rich domain at the C terminus. The N-terminal RRM domain by itself provides the editing activity of ORRM3. In yeast-two hybrid assays, ORRM3 interacts with RIP1, ORRM2 and with itself. Transient silencing of ORRM2 in the orrm3 mutant further impairs the editing activity at sites controlled by both ORRM2 and ORRM3. Identification of the effect of ORRM2 and ORRM3 on RNA editing reveals a previously undescribed role of RRM-containing proteins as mitochondrial RNA editing factors.
Highlights
In land plants, C-to-U RNA editing is a posttranscriptional modification that occurs in plastids and mitochondrial transcripts, often resulting in changes in the amino acid sequence from what the genomic sequence predicts
Transient silencing of ORRM2 and ORRM3 leads to mitochondrial editing defects
In order to characterize the function of the ORRM family proteins in RNA editing, we performed Virus Induced Gene Silencing (VIGS) to transiently silence two Arabidopsis genes whose RNA Recognition Motif (RRM) are closely related to the RRM found in ORRM1 a known plastid editing factor (Supplementary Figure S1)
Summary
C-to-U RNA editing is a posttranscriptional modification that occurs in plastids and mitochondrial transcripts, often resulting in changes in the amino acid sequence from what the genomic sequence predicts. The amino acid encoded by edited transcripts is usually more conserved than the one predicted by unedited transcripts [4]. The composition of the RNA editosome is not yet fully understood cis- as well as trans-factors have been found to be essential for the editing process. Members of the PLS subclass of the pentatricopeptide repeat (PPR) motif-containing family are site-specific recognition factors required for RNA editing in plant organelles [10,11]. Mutagenesis of conserved deaminase residues in DYW1, QED1 and RARE1 resulted in loss of editing activity [16,17], further strengthening the hypothesis that the enzyme activity resides in the DYW domain
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