Seminar by Prof. Oren OSTERSETZER-BIRAN, The Hebrew University of Jerusalem, Israël,

N⁶-adenosine methylation (m⁶A): an internal RNA-base modification that may affect gene-expression programs in angiosperms mitochondria -

invited by J. Gualberto et P. Giegé

Mitochondria play a critical role in the generation of metabolic energy in eukaryotic cells, and are associated with growth, differentiation and aging. As relicts of bacterial endosymbionts, mitochondria contain their own genetic system (mtDNA) and protein translation apparatus. The expression of the mtDNA in plants is highly complex, particularly at the posttranscriptional level. Following initial transcription, the polycistronic pre-RNAs in plant mitochondria undergo extensive processing and modifications (e.g., trimming, splicing, C-to-U editing and other RNA- base modifications), in order to become mature functional RNAs that can be translated by the organellar ribosomes.

Our study focuses on N⁶-methylation of Adenosine ribonucleotides (m⁶A) in plant mitochondria. The biological significance of m⁶A RNA-modifications in bacteria and eukaryotic systems is under investigation, but it’s widely accepted that m⁶A mediates structural switches that affect RNA stability or activity. By performing m⁶A-RNA-seq analyses of mitochondrial transcriptomes, we provide with a comprehensive data of the landscapes of m⁶A RNA-modifications in angiosperms mitochondria. The data indicate that m⁶A methylations target all types of mtRNAs, including structural RNAs, coding-sequences, introns, UTRs, as well as transcribed-intergenic RNA species. Interestingly, while noncoding RNAs undergo multiple m⁶A modifications along their transcripts, in mRNAs the m⁶A modification is predominantly positioned within the start-codon and may modulates mtRNA translatability. These findings might indicate that m⁶A controls gene-expression programs in plant mitochondria, and provide with new insights into the significance of RNA-base modifications in eukaryotic organelles.