N 6 ‐Methyladenosine mRNA methylation is important for salt stress tolerance in Arabidopsis

SUMMARY As the most abundant internal modification of mRNA, N 6 ‐methyladenosine (m 6 A) methylation of RNA is emerging as a new layer of epitranscriptomic gene regulation in cellular processes, including embryo development, flowering‐time control, microspore generation and fruit ripening, in plants. However, the cellular role of m 6 A in plant responses to environmental stimuli remains largely unexplored. In this study, we show that m 6 A methylation plays an important role in salt stress tolerance in Arabidopsis . All mutants of m 6 A writer components, including MTA, MTB, VIRILIZER (VIR) and HAKAI, displayed salt‐sensitive phenotypes in an m 6 A‐dependent manner. The vir mutant, in which the level of m 6 A was most highly reduced, exhibited salt‐hypersensitive phenotypes. Analysis of the m 6 A methylome in the vir mutant revealed a transcriptome‐wide loss of m 6 A modification in the 3ʹ untranslated region (3ʹ‐UTR). We demonstrated further that VIR ‐mediated m 6 A methylation modulates reactive oxygen species homeostasis by negatively regulating the mRNA stability of several salt stress negative regulators, including ATAF1 , GI and GSTU17 , through affecting 3ʹ‐UTR lengthening linked to alternative polyadenylation. Our results highlight the important role played by epitranscriptomic mRNA methylation in the salt stress response of Arabidopsis and indicate a strong link between m 6 A methylation and 3ʹ‐UTR length and mRNA stability during stress adaptation.