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Although several studies have shown that AlkB homolog (ALKBH) proteins are potential RNA demethylases (referred to as 'erasers'), biological functions of only a few ALKBH proteins have been characterized to date. In this study, we determined the function of ALKBH9C (At4g36090) in seed germination and seedling growth of Arabidopsis thaliana in response to abiotic stress and abscisic acid (ABA). Seed germination of the alkbh9c mutant was delayed in response to salt, drought, cold and ABA. Moreover, seedling growth of the mutant was repressed under salt stress or ABA but enhanced under drought conditions. Notably, the stress‐responsive phenotypes were associated with the altered expression of several m6A‐modified transcripts related to salt, drought or ABA response. Global m6A levels were increased in the alkbh9c mutant, and ALKBH9C bound to m6A‐modified RNAs and had in vitro m6A demethylase activity, suggesting its potential role as an m6A eraser. The m6A levels in several stress‐responsive genes were increased in the alkbh9c mutant, and the stability of m6A‐modified transcripts was altered in the mutant. Collectively, our results suggest that m6A eraser ALKBH9C is crucial for seed germination and seedling growth of Arabidopsis in response to abiotic stresses or ABA via affecting the stability of stress‐responsive transcripts. Summary statement: Addition and removal of methylation marks in RNAs is critical for the response of plants to abiotic stresses and abscisic acid. In this study, we show that ALKBH9C is a potential m6A demethylase that plays a crucial role in seed germination and seedling growth of Arabidopsis in response to salt stress, drought stress, and abscisic acid. [ABSTRACT FROM AUTHOR]

N6‐methyladenosine (m6A) is an abundant methylation mark in eukaryotic mRNAs. It is installed and removed by methyltransferases ("writers") and demethylases ("erasers"), respectively. A recent study has demonstrated that alpha‐ketoglutarate‐dependent dioxygenase homolog 10B (ALKBH10B) is an mRNA m6A eraser affecting floral transition in Arabidopsis thaliana. However, the roles of m6A eraser proteins, including ALKHB10B, in plant adaptation to abiotic stresses are largely unknown. In this study, we aimed to determine the role of ALKBH10B in the response of A. thaliana to abiotic stresses and abscisic acid (ABA). The m6A level increased in response to salt stress, and m6A levels in alkbh10b mutants were higher than those in the wild‐type under both normal and salt stress conditions. Germination of alkbh10b mutant seeds was markedly delayed under salt stress but not under dehydration, cold, or ABA conditions. Seedling growth and survival rate of alkbh10b mutants were enhanced under salt stress. Notably, salt‐tolerant phenotypes of alkbh10b mutants were correlated with decreased levels of several m6A‐modified genes, including ATAF1, BGLU22, and MYB73, which are negative effectors of salt stress tolerance. In response to ABA, both seedling and root growth of alkbh10b mutants were inhibited via upregulating ABA signaling‐related genes, including ABI3 and ABI4. Collectively, these findings indicate that ALKBH10B‐mediated m6A demethylation affects the transcript levels of stress‐responsive genes, which are important for seed germination, seedling growth, and survival of Arabidopsis thaliana in response to salt stress or ABA. [ABSTRACT FROM AUTHOR]