N-6-methyladenosine (m(6)A) is a dynamic, reversible, covalently modified ribonucleotide that occurs predominantly toward 3' ends of eukaryotic mRNAs and is essential for their proper function and regulation. In Arabidopsis thaliana, many RNAs contain at least one m(6)A site, yet the transcriptome-wide function of m(6)A remains mostly unknown. Here, we show that many m(6)A-modified mRNAs in Arabidopsis have reduced abundance in the absence of this mark. The decrease in abundance is due to transcript destabilization caused by cleavage occurring 4 or 5 nt directly upstream of unmodified m(6)A sites. Importantly, we also find that, upon agriculturally relevant salt treatment, m(6)A is dynamically deposited on and stabilizes transcripts encoding proteins required for salt and osmotic stress response. Overall, our findings reveal that m(6)A generally acts as a stabilizing mark through inhibition of site-specific cleavage in plant transcriptomes, and this mechanism is required for proper regulation of the salt-stress-responsive transcriptome.
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