N6-methyladenosine (m6A) is the most prevalent epitranscriptomic modification found in eukaryotic mRNA. The levels of m6A are determined by the coordinated actions of methyltransferases ('writers') and demethylases ('erasers') that introduce and remove m6A marks, respectively. Recent studies have demonstrated that chloroplast mRNAs are highly rich in m6A; however, the significance of m6A methylation in chloroplasts remains unknown. As no mRNA m6A writers and erasers have been identified in chloroplasts, in this study, we artificially imported ALKBH10B, a well-characterised mRNA m6A eraser localised in the nucleus and cytoplasm in Arabidopsis (Arabidopsis thaliana), into chloroplasts to uncover the potential impact of m6A modification in chloroplasts on photosynthesis and abiotic stress response. We found that the chloroplast-targeted ALKBH10B successfully removes m6A marks from numerous mRNAs in chloroplasts. Notably, the ALKBH10B-mediated demethylation f m6A marks in chloroplast mRNAs enhanced salt and drought tolerance in Arabidopsis by modulating the stability of m6A-modified photosynthesis-associated mRNAs. Overall, our findings reveal that ALKBH10B-mediated m6A demethylation in chloroplast mRNAs enhances photosynthesis and stress tolerance, highlighting that modulation of RNA methylation in chloroplasts can be a potential means for breeding stress-tolerant plants.
Han et al. (Thu,) studied this question.