Intron RNA editing is essential for splicing in plant mitochondria

Abstract

Most plant mitochondria messenger RNAs (mRNAs) undergo editing through C-to-U conversions located mainly in exon sequences. However, some RNA editing events are found in non-coding regions at critical positions in the predicted secondary and tertiary structures of introns, suggesting that RNA editing could be important for splicing. Here, we studied the relationships between editing and splicing of the mRNA encoding the ribosomal protein S10 (rps10), which has a group II intron and five editing sites. Two of them, C2 and C3, predicted to stabilize the folded structure of the intron necessary for splicing, were studied by using rps10 mutants introduced into isolated potato mitochondria by electroporation. While mutations of C2 involved in EBS2/IBS2 interactions did not affect splicing, probably by the presence of an alternative EBS2′ region in domain I of the intron, the edition of site C3 turned out to be critical for rps10 mRNA splicing; only the edited (U) form of the transcript was processed. Interestingly, RNA editing was strongly reduced in transcripts from two different intronless genes, rps10 from potato and cox2 from wheat, suggesting that efficient RNA processing may require a close interaction of factors engaged in different maturation processes. This is the first report linking editing and splicing in conditions close to the in vivo situation.

Chloroplast RNA editing going extreme: more than 3400 events of C-to-U editing in the chloroplast transcriptome of the lycophyte Selaginella uncinata

“…Organelle introns (mainly of the group II type in plant chloroplasts and mitochondria) are characterized by conserved secondary and tertiary structures that have previously been shown to be affected by RNA editing in some cases (see e.g., Lippok et al 1994;Börner et al 1995;Carrillo and Bonen 1997;Carrillo et al 2001;Castandet et al 2010;Bégu et al 2011;Farré et al 2012). To detect RNA editing in intron sequences we used a strategy to aim for partially matured transcripts.…”

Monilophyte mitochondrial rps1 genes carry a unique group II intron that likely originated from an ancient paralog in rpl2

“…Several plant mitochondrial introns have been shown to be subject to RNA editing and at least some cases of intron editing are very likely required to restore the ability for splicing (Lippok et al 1994;Carrillo and Bonen 1997;Carrillo et al 2001;Castandet et al 2010;Bégu et al 2011;Farré et al 2012;Oldenkott et al 2014). Using a combined strategy to obtain cDNAs of intron sequences, we identified several events of RNA editing in the two introns under investigation ( Table 1).…”

Electroporation of DNA into Physarum polycephalum Mitochondria: Effects on Transcription and RNA Editing in Isolated Organelles

“…Plasmid constructs introduced into mitochondria isolated from wheat embryos [23], etiolated maize seedlings [29], and potato tubers [31] support transcription, splicing, and C to U editing, providing a means of investigating editing signals [22,25,26] and the interplay between different forms of RNA processing [27,29,30,31]. The studies in plant mitochondria utilized two distinct sets of electroporation and expression conditions, and variations of each were tested using isolated P. polycephalum mitochondria.…”

“…An early study using mammalian mitochondria demonstrated DNA uptake and the effects of field strength on mitochondrial function, but did not examine transcriptional activity [21]. This methodology was subsequently adapted to study transcription, splicing, and RNA editing in mitochondria from wheat [22,23,24,25,26,27], maize and sorghum [28,29], and potato [30,31]. Accurate C to U editing of transcripts derived from chimeric genes was observed in each of these systems, allowing localization of the cis -acting signals essential for editing [22,25].…”