Editor-in-charge |Wang Yi
6-Methyladenosine(N6-methyladenosine, M6A) is the most abundant internal modification on eukaryotic mRNA, which affects various RNA metabolic processes such as mRNA stability, splicing of precursor RNA, polyadenylation, mRNA trafficking, and translation initiation (Zaccara, S.). et al. 2019)。In recent years, a number of studies have confirmed that M6A modification plays an important role in plant growth and development, biotic and abiotic stress response, and crop trait improvement (Shao, Y.). et al. 2021; shen, l. et al. 2023)。Especially when plants are subjected to external stress, the dynamic reversible changes of M6A modification can quickly regulate gene expression, thereby endowing plants with strong environmental adaptability (Hu, J.). et al. 2022)。However, the mechanism by which plants use this chemical modification to rapidly adjust their growth under stress conditions is still unclear.
Plant stress hormone ABA plays a vital role in the survival of plants under various stresses such as drought and salinity. The results showed that abiotic stress could rapidly induce the accumulation of ABA in plants, and when the ABA receptor Pyr Pyl protein sensed the ABA molecule, it would competitively bind to the co-receptor PP2C protein, thereby relieving the inhibition of the PP2C protein on SNRK2S kinase, a key positive regulator in the ABA signaling pathway. The release of SNRK2S can activate a series of response factors of the ABA signaling pathway, which in turn can help plants resist stress (Chen, K.). et al. 2020)。Therefore, it is of great significance to further reveal the molecular mechanism and genetic network of fine regulation during ABA signal sensing and transduction for targeted improvement of plant stress tolerance.
Recently, the National University of Singapore's Temasek Institute of Life SciencesYu HaoAcademician team withShen LisaThe research group of researchers cooperates innature plantsPublished a post entitled :n-methyladenosine-mediated feedback regulation of abscisic acid perception viaphase-separated ect8 condensatesinarabidopsisrevealed a novel mechanism by which M6A modification and its recognition protein ECT8 feedback regulate ABA signal perception.
This study found that the M6A-modified recognition protein ECT8 can act as a molecular receptor for intracellular ABA concentration, directly regulating the ABA signaling pathway and the response of Arabidopsis thaliana to drought stress. ECT8 mutants had no obvious phenotype under normal growth conditions, but exhibited an ABA hypersensitive phenotype under ABA treatment. Under the induction of ABA, the expression of ECT8 increased rapidly, and its protein level also increased significantly, while the ECT8 protein diffused in the cytoplasm formed a dynamic granular structure in the cell. The analysis showed that ECT8 protein could exhibit liquid-liquid phase separation in vivo and in vitro under the induction of ABA or solution environment, forming a dynamic droplet-like structure. The phase separation of ECT8 is dependent on its N-terminal IDR2 (intrinsically disordered region 2) domain, which is regulated by the M6A-modified mRNA and its C-terminal YTH domain (M6A-binding domain). The ECT8 condensate formed by phase separation is necessary for the ABA signal transduction process, and the corresponding phase separation defective transgenic materials cannot restore the ABA hypersensitive phenotype of ECT8 mutants.
Further studies showed that ECT8 protein could bind to RBP47B, the core regulatory protein of stress granules, confirming that ECT8 condensate was a component of stress granules, and mRNA carrying M6A modification was aggregated in stress granules under ABA treatment or stress stress. The third-generation sequencing technology-nanopore sequencing was used to analyze the mRNA composition of stress granules under ABA treatment conditions, and the dynamic regulation effect of ECT8 on M6A-modified mRNA in stress granules was clarified. Further analysis of the m6a characteristics of the mRNA of stress granules, the research group proposed that m6a modification may be an important marker for plants to sort mRNA into stress granules in response to the increase of ABA concentration. Notably, the ECT8 condensate formed upon ABA treatment specifically recruited M6A-modified PYL7 mRNA, which encodes the ABA receptor protein. Further studies have found that the mRNA retention function of ECT8 in the stress granules blocks the translation process of PYL7, thereby attenuating the excessive accumulation of PYL7 protein and inhibiting the perception of ABA signal. This feedback regulation effectively avoided the overreaction of plants to the increase in ABA concentration, which helped the plants adapt to the arid environment (Figure 1).
Figure 1: ECT8 feedback regulates the working model of ABA signal perception.
In addition, a variety of stress conditions, such as high temperature, salt stress and osmotic stress, could induce the formation of phase-separated stress granules of ECT8 protein, indicating that the formation of ECT8 aggregates of M6A recognition protein is one of the important adaptation strategies of plants to cope with multiple stress stresses.
In summary, this study proposed and elucidated a new mechanism for M6A modification and its recognition protein ECT8 to sense the changes in intracellular ABA concentration through liquid-liquid phase separation, and to isolate ABA receptor mRNA, so as to achieve feedback regulation of ABA signal perception and adversity stress response. This study revealed the important role of stress granules and M6A modification in synergistically regulating plant stress response, and provided a new idea for improving crop stress tolerance.
Yu HaoAcademician andShen LisaThe researcher is the co-corresponding author of the **, Yu Hao's research groupWu XiaoweiThe Ph.D. is the first author of the **. Su TingtingZhang SongyaoDr. andZhang YuPh.D. and others were also involved in the study. The research was supported by the National Society for Singapore**, the National University of Singapore and Temasek Life Sciences.
References:zaccara, s., ries, r. j. &jaffrey, s. r. reading, writing and erasing mrna methylation. nat. rev. mol. cell biol. 20, 608-624 (2019).shao, y., wong, c. e., shen, l. &yu, h. n6-methyladenosine modification underlies messenger rna metabolism and plant development. curr. opin. plant biol. 63, 102047 (2021).shen, l., ma, j., li, p., wu, y. &yu, h. recent advances in the plant epitranscriptome. genome biol 24, 43, doi:10.1186/s13059-023-02872-6 (2023).hu, j., cai, j., xu, t. &kang, h. epitranscriptomic mrna modifications governing plant stress responses: underlying mechanism and potential application. plant biotechnol. j. 20, 2245-2257 (2022).chen, k. et al. abscisic acid dynamics, signaling, and functions in plants. j. integr. plant biol. 62, 25-54 (2020).**Links:
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