The RNA N^(6)-methyladenosine demethylase ALKBH9B modulates ABA responses in Arabidopsis

The mRNA modification N^(6)-methyladenosine(m^(6)A)plays vital roles in plant development and biotic and abiotic stress responses.The RNA m^(6)A demethylase ALKBH9 B can remove m^(6)A in alfalfa mosaic virus RNA and plays roles in alfalfa mosaic virus infection in Arabidopsis.However,it is unknown whether ALKBH9 B also exhibits demethylation activity and has a biological role in endogenous plant mRNA.We demonstrated here that mRNA m^(6)A modification is induced by the phytohormone abscisic acid(ABA)and that ALKBH9 B has m^(6)A demethylation activity on endogenous mRNA.Knocking out ALKBH9 B led to hypersensitivity to ABA treatment during seed germination and early seedling development.We further showed that ALKBH9 B removes the m^(6)A 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 ALKBH9 B 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 m^(6)A modification in ABA responses and highlight the role of ALKBH9 Bmediated m^(6)A demethylation in regulating ABA responses post-transcriptionally.