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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 m 6 A-modified transcripts related to salt, drought or ABA response. Global m 6 A levels were increased in the alkbh9c mutant, and ALKBH9C bound to m 6 A-modified RNAs and had in vitro m 6 A demethylase activity, suggesting its potential role as an m 6 A eraser. The m 6 A levels in several stress-responsive genes were increased in the alkbh9c mutant, and the stability of m 6 A-modified transcripts was altered in the mutant. Collectively, our results suggest that m 6 A 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., (© 2022 John Wiley & Sons Ltd.)

To improve future agricultural production, major technological advances are required to increase crop production and yield. Targeting the coding region of genes via the Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated Protein (CRISPR/Cas) system has been well established and has enabled the rapid generation of transgene-free plants, which can lead to crop improvement. The emergence of the CRISPR/Cas system has also enabled scientists to achieve cis-regulatory element (CRE) editing and, consequently, engineering endogenous critical CREs to modulate the expression of target genes. Recent genome-wide association studies have identified the domestication of natural CRE variants to regulate complex agronomic quantitative traits and have allowed for their engineering via the CRISPR/Cas system. Although engineering plant CREs can be advantageous to drive gene expression, there are still many limitations to its practical application. Here, we review the current progress in CRE editing and propose future strategies to effectively target CREs for transcriptional regulation for crop improvement., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Epitranscriptomics has added a new layer of regulatory machinery to eukaryotes, and the advancement of sequencing technology has revealed more than 170 post-transcriptional modifications in various types of RNAs, including messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), and long non-coding RNA (lncRNA). Among these, N6-methyladenosine (m 6 A) and N5-methylcytidine (m 5 C) are the most prevalent internal mRNA modifications. These regulate various aspects of RNA metabolism, mainly mRNA degradation and translation. Recent advances have shown that regulation of RNA fate mediated by these epitranscriptomic marks has pervasive effects on a plant's development and responses to various biotic and abiotic stresses. Recently, it was demonstrated that the removal of human-FTO-mediated m 6 A from transcripts in transgenic rice and potatoes caused a dramatic increase in their yield, and that the m 6 A reader protein mediates stress responses in wheat and apple, indicating that regulation of m 6 A levels could be an efficient strategy for crop improvement. However, changing the overall m 6 A levels might have unpredictable effects; therefore, the identification of precise m 6 A levels at a single-base resolution is essential. In this review, we emphasize the roles of epitranscriptomic modifications in modulating molecular, physiological, and stress responses in plants, and provide an outlook on epitranscriptome engineering as a promising tool to ensure food security by editing specific m 6 A and m 5 C sites through robust genome-editing technology.

N 6 -methyladenosine (m 6 A) 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 m 6 A eraser affecting floral transition in Arabidopsis thaliana. However, the roles of m 6 A 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 m 6 A level increased in response to salt stress, and m 6 A 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 m 6 A-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 m 6 A 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., (© 2021 Scandinavian Plant Physiology Society.)