C-methyladenosine in tRNA promotes protein translation by facilitating the decoding of tandem mA-tRNA-dependent codons.

RNA modification C-methyladenosine (mA) exists in both rRNA and tRNA of Escherichia coli (E. coli), installed by the methyltransferase RlmN using a radical-S-adenosylmethionine (SAM) mechanism. However, the precise function of mA in tRNA and its ubiquity in plants have remained unclear. Here we discover the presence of mA in chloroplast rRNA and tRNA, as well as cytosolic tRNA, in multiple plant species. We identify six mA-modified chloroplast tRNAs and two mA-modified cytosolic tRNAs across different plants. Furthermore, we characterize three Arabidopsis mA methyltransferases-RLMNL1, RLMNL2, and RLMNL3-which methylate chloroplast rRNA, chloroplast tRNA, and cytosolic tRNA, respectively. Our findings demonstrate that mA37 promotes a relaxed conformation of tRNA, enhancing translation efficiency in chloroplast and cytosol by facilitating decoding of tandem mA-tRNA-dependent codons. This study provides insights into the molecular function and biological significance of mA, uncovering a layer of translation regulation in plants.