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ABSTRACT Modifications to RNA have recently been recognized as a pivotal regulator of gene expression in living organisms. More than 170 chemical modifications have been identified in RNAs, with N6‐methyladenosine (m6A) being the most abundant modification in eukaryotic mRNAs. The addition and removal of m6A marks are catalyzed by methyltransferases (referred to as “writers”) and demethylases (referred to as “erasers”), respectively. In addition, the m6A marks in mRNAs are recognized and interpreted by m6A‐binding proteins (referred to as “readers”), which regulate the fate of mRNAs, including stability, splicing, transport, and translation. Therefore, exploring the mechanism underlying the m6A reader‐mediated modulation of RNA metabolism is essential for a much deeper understanding of the epigenetic role of RNA modification in plants. Recent discoveries have improved our understanding of the functions of m6A readers in plant growth and development, stress response, and disease resistance. This review highlights the latest developments in m6A reader research, emphasizing the diverse RNA‐binding domains crucial for m6A reader function and the biological and cellular roles of m6A readers in the plant response to developmental and environmental signals. Moreover, we propose and discuss the potential future research directions and challenges in identifying novel m6A readers and elucidating the cellular and mechanistic role of m6A readers in plants. [ABSTRACT FROM AUTHOR]

Climate change has emerged as a crucial global issue that significantly threatens the survival of plants. In particular, low temperature (LT) is one of the critical environmental factors that influence plant morphological, physiological, and biochemical changes during both the vegetative and reproductive growth stages. LT, including abrupt drops in temperature, as well as winter conditions, can cause detrimental effects on the growth and development of tomato plants, ranging from sowing, transplanting, truss appearance, flowering, fertilization, flowering, fruit ripening, and yields. Therefore, it is imperative to understand the comprehensive mechanisms underlying the adaptation and acclimation of tomato plants to LT, from the morphological changes to the molecular levels. In this review, we discuss the previous and current knowledge of morphological, physiological, and biochemical changes, which contain vegetative and reproductive parameters involving the leaf length (LL), plant height (PH) stem diameter (SD), fruit set (FS), fruit ripening (FS), and fruit yield (FY), as well as photosynthetic parameters, cell membrane stability, osmolytes, and ROS homeostasis via antioxidants scavenging systems during LT stress in tomato plants. Moreover, we highlight recent advances in the understanding of molecular mechanisms, including LT perception, signaling transduction, gene regulation, and fruit ripening and epigenetic regulation. The comprehensive understanding of LT response provides a solid basis to develop the LT-resistant varieties for sustainable tomato production under the ever-changing temperature fluctuations. [ABSTRACT FROM AUTHOR]

N6‐methyladenosine (m6A) is an mRNA modification widely found in eukaryotes and plays a crucial role in plant development and stress responses. FIONA1 (FIO1) is a recently identified m6A methyltransferase that regulates Arabidopsis (Arabidopsis thaliana) floral transition; however, its role in stress response remains unknown. In this study, we demonstrate that FIO1‐mediated m6A methylation plays a vital role in salt stress response in Arabidopsis. The loss‐of‐function fio1 mutant was sensitive to salt stress. Importantly, the complementation lines expressing the wild‐type FIO1 exhibited the wild‐type phenotype, whereas the complementation lines expressing the mutant FIO1m, in which two critical amino acid residues essential for methyltransferase activity were mutated, did not recover the wild‐type phenotype under salt stress, indicating that the salt sensitivity is associated with FIO1 methyltransferase activity. Furthermore, FIO1‐mediated m6A methylation regulated ROS production and affected the transcript level of several salt stress‐responsive genes via modulating their mRNA stability in an m6A‐dependent manner in response to salt stress. Importantly, FIO1 is associated with salt stress response by specifically targeting and differentially modulating several salt stress‐responsive genes compared with other m6A writer. Collectively, our findings highlight the molecular mechanism of FIO1‐mediated m6A methylation in the salt stress adaptation. Summary Statement: FIONA1 (FIO1), a recently identified m6A methyltransferase, plays a vital role in salt stress response by modulating the stability of several m6A‐modified salt stress‐responsive genes in Arabidopsis thaliana. [ABSTRACT FROM AUTHOR]

Plant glycine-rich RNA-binding proteins (GRPs) play crucial roles in the response to environmental stresses. However, the functions of AtGRP7 in plants under heavy metal stress remain unclear. In the present study, in Arabidopsis, the transcript level of AtGRP7 was markedly increased by Ni but was decreased by Pb. AtGRP7-overexpressing plants improved Ni tolerance, whereas the knockout mutant (grp7) was more susceptible than the wild type to Ni. In addition, grp7 showed greatly enhanced Pb tolerance, whereas overexpression lines showed high Pb sensitivity. Ni accumulation was reduced in overexpression lines but increased in grp7, whereas Pb accumulation in grp7 was lower than that in overexpression lines. Ni induced glutathione synthase genes GS1 and GS2 in overexpression lines, whereas Pb increased metallothionein genes MT4a and MT4b and phytochelatin synthase genes PCS1 and PCS2 in grp7. Furthermore, Ni increased CuSOD1 and GR1 in grp7, whereas Pb significantly induced FeSOD1 and FeSOD2 in overexpression lines. The mRNA stability of GS2 and PCS1 was directly regulated by AtGRP7 under Ni and Pb, respectively. Collectively, these results indicate that AtGRP7 plays a crucial role in Ni and Pb tolerance by reducing Ni and Pb accumulation and the direct or indirect post-transcriptional regulation of genes related to heavy metal chelators and antioxidant enzymes. [ABSTRACT FROM AUTHOR]

Membraneless biomolecular condensates form distinct subcellular compartments that enable a cell to orchestrate numerous biochemical reactions in a spatiotemporal-specific and dynamic manner. Liquid‒liquid phase separation (LLPS) facilitates the formation of membraneless biomolecular condensates, which are crucial for many cellular processes in plants, including embryogenesis, the floral transition, photosynthesis, pathogen defense, and stress responses. The main component required for LLPS is a protein harboring key characteristic features, such as intrinsically disordered regions, low-complexity sequence domains, and prion-like domains. RNA is an additional component involved in LLPS. Increasing evidence indicates that modifications in proteins and RNAs play pivotal roles in LLPS. In particular, recent studies have indicated that N6-methyladenosine (m6A) modification of messenger RNA is crucial for LLPS in plants and animals. In this review, we provide an overview of recent developments in the role of mRNA methylation in LLPS in plant cells. Moreover, we highlight the major challenges in understanding the pivotal roles of RNA modifications and elucidating how m6A marks are interpreted by RNA-binding proteins crucial for LLPS. An overview of recent developments and major challenges in understanding the role of N6-methyladenosine RNA methylation in liquid‒liquid phase separation in plant cells. [ABSTRACT FROM AUTHOR]

N6-methyladenosine (m6A), which is added, removed, and interpreted by m6A writers, erasers, and readers, respectively, is the most abundant modification in eukaryotic mRNAs. The m6A marks play a pivotal role in the regulation of floral transition in plants. FLOWERING LOCUS K (FLK), an RNA-binding protein harboring K-homology (KH) motifs, is known to regulate floral transition by repressing the levels of a key floral repressor FLOWERING LOCUS C (FLC) in Arabidopsis. However, the molecular mechanism underlying FLK-mediated FLC regulation remains unclear. In this study, we identified FLK as a novel mRNA m6A reader protein that directly binds the m6A site in the 3ʹ-untranslated region of FLC transcripts to repressing FLC levels by reducing its stability and splicing. Importantly, FLK binding of FLC transcripts was abolished in vir-1 , an m6A writer mutant, and the late-flowering phenotype of the flk mutant could not be rescued by genetic complementation using the mutant FLK m gene, in which the m6A reader encoding function was eliminated, indicating that FLK binds and regulates FLC expression in an m6A-dependent manner. Collectively, our study has addressed a long-standing question of how FLK regulates FLC transcript levels and established a molecular link between the FLK-mediated recognition of m6A modifications on FLC transcripts and floral transition in Arabidopsis. FLK, an RNA-binding protein harboring KH) motifs, is known to regulate floral transition by repressing FLC levels in Arabidopsis , but the underlying molecular mechanism remains unclear. In this study, the authors identifies FLK as a novel mRNA m6A reader protein that directly binds to the m6A site in the 3ʹ-untranslated region of FLC transcripts, thus repressing FLC levels by reducing its stability and splicing. Their results suggest a molecular link between the FLK-mediated recognition of m6A modifications on FLC transcripts and floral transition in Arabidopsis. [ABSTRACT FROM AUTHOR]

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]

Summary: Plants inevitably encounter environmental adversities, including abiotic and biotic stresses, which significantly impede plant growth and reduce crop yield. Thus, fine‐tuning the fate and function of stress‐responsive RNAs is indispensable for plant survival under such adverse conditions. Recently, post‐transcriptional RNA modifications have been studied as a potent route to regulate plant gene expression under stress. Among over 160 mRNA modifications identified to date, N6‐methyladenosine (m6A) in mRNAs is notable because of its multifaceted roles in plant development and stress response. Recent transcriptome‐wide mapping has revealed the distribution and patterns of m6A in diverse stress‐responsive mRNAs in plants, building a foundation for elucidating the molecular link between m6A and stress response. Moreover, the identification and characterization of m6A writers, readers and erasers in Arabidopsis and other model crops have offered insights into the biological roles of m6A in plant abiotic stress responses. Here, we review the recent progress of research on mRNA modifications, particularly m6A, and their dynamics, distribution, regulation and biological functions in plant stress responses. Further, we posit potential strategies for breeding stress‐tolerant crops by engineering mRNA modifications and propose the future direction of research on RNA modifications to gain a much deeper understanding of plant stress biology. [ABSTRACT FROM AUTHOR]

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 (m6A) and N5-methylcytidine (m5C) 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 m6A from transcripts in transgenic rice and potatoes caused a dramatic increase in their yield, and that the m6A reader protein mediates stress responses in wheat and apple, indicating that regulation of m6A levels could be an efficient strategy for crop improvement. However, changing the overall m6A levels might have unpredictable effects; therefore, the identification of precise m6A 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 m6A and m5C sites through robust genome-editing technology. [ABSTRACT FROM AUTHOR]