The unique topologies of N6-Adenosine methylation (m6A) in land-plant mitochondria and their putative effects on organellar gene-expression

Mitochondria are the main source of ATP production and also contribute to many other processes central to cellular function. Mitochondrial activities have been linked with growth, differentiation and aging. As relicts of bacterial endosymbionts, these organelles contain their own genetic system (i.e., mitogenome or mtDNA). The expression of the mtDNA in plants is complex, particularly at the posttranscriptional level. Following transcription, the polycistronic pre-RNAs in plant mitochondria are processed into individual RNAs, which then undergo extensive modifications, as trimming, splicing and C-to-U editing, before being translated by organellar ribosomes. Our study focuses on N6-methylation of Adenosine ribonucleotides (m6A-RNA) in plant mitochondria. m6A is the most common modification in eukaryotic mRNAs. The biological significance of this highly dynamic modification is under investigation, but it is widely accepted that m6A mediates structural switches that affect RNA stability and activity. By performing m6A-pulldown/RNA-seq (m6A-RIP-seq) analyses of Arabidopsis and cauliflower mitochondrial transcripts (mtRNAs), we provide with detail information on the m6A landscapes in angiosperms mitochondria. The results indicate that m6A targets different types of mtRNAs, including coding sequences, UTRs, introns and non-coding RNA species. While introns and noncoding-RNAs undergo multiple m6A modifications along the transcript, in mRNAs m6A-modifications are preferably positioned near start-codons, and may modulate the translatability of the m6A-modified transcripts.