Abstract:

The mRNA modification N⁶-methyladenosine (m⁶A) plays vital roles in plant development and biotic and abiotic stress responses. The RNA m⁶A demethylase ALKBH9B can remove m⁶A in alfalfa mosaic virus RNA and plays roles in alfalfa mosaic virus infection in Arabidopsis. However, it is unknown whether ALKBH9B also exhibits demethylation activity and has a biological role in endogenous plant mRNA. We demonstrated here that mRNA m⁶A modification is induced by the phytohormone abscisic acid (ABA) and that ALKBH9B has m⁶A demethylation activity on endogenous mRNA. Knocking out ALKBH9B led to hypersensitivity to ABA treatment during seed germination and early seedling development. We further showed that ALKBH9B removes the m⁶A modification in the ABA INSENSITIVE 1 (ABI1) and BRI1-EMS-SUPPRESSOR 1 (BES1) transcripts following ABA treatment, affecting the stability of these mRNAs. Furthermore, we determined that ALKBH9B acts genetically upstream of the transcription factors ABI3 and ABI5, and its regulatory function in ABA responses depended on ABI3 and ABI5. Our findings reveal the important roles of the m⁶A modification in ABA responses and highlight the role of ALKBH9B-mediated m⁶A demethylation in regulating ABA responses post-transcriptionally.