m 6 A Demethylation in Chloroplasts Enhances Stress Tolerance by Modulating the Stability of Photosynthesis‐Associated mRNAs in Arabidopsis

ABSTRACT N 6 ‐methyladenosine (m 6 A) is the most prevalent epitranscriptomic modification found in eukaryotic mRNA. The levels of m 6 A are determined by the coordinated actions of methyltransferases (‘writers’) and demethylases (‘erasers’) that introduce and remove m 6 A marks, respectively. Recent studies have demonstrated that chloroplast mRNAs are highly rich in m 6 A; however, the significance of m 6 A methylation in chloroplasts remains unknown. As no mRNA m 6 A writers and erasers have been identified in chloroplasts, in this study, we artificially imported ALKBH10B, a well‐characterised mRNA m 6 A eraser localised in the nucleus and cytoplasm in Arabidopsis ( Arabidopsis thaliana ), into chloroplasts to uncover the potential impact of m 6 A modification in chloroplasts on photosynthesis and abiotic stress response. We found that the chloroplast‐targeted ALKBH10B successfully removes m 6 A marks from numerous mRNAs in chloroplasts. Notably, the ALKBH10B‐mediated demethylation f m 6 A marks in chloroplast mRNAs enhanced salt and drought tolerance in Arabidopsis by modulating the stability of m 6 A‐modified photosynthesis‐associated mRNAs. Overall, our findings reveal that ALKBH10B‐mediated m 6 A 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.