The receptor-like kinase FERONIA (FER), together with its ligand rapid alkalinization factor 1 (RALF1) peptide, plays a crucial role in regulating stress responses, including its involvement in modulating abscisic acid (ABA) signaling. FER has been shown to activate ABA Insensitive 2 (ABI2) in the cytoplasm, leading to the suppression of ABA signaling. However, its regulation of nucleus events in the ABA response remains unclear. FREE1, identified as a plant-specific component of the endosomal sorting complex required for transport (ESCRT) in eukaryotes, serves as an important negative regulator in ABA signaling. In this study, we elucidate that upon RALF1 treatment, FER phosphorylates FREE1, promoting the accumulation of FREE1 protein in the nucleus in Arabidopsis (Arabidopsis thaliana). Consequently, FREE1 suppresses ABA sensitivity by inhibiting the expression of ABA-response genes. Mutating the six identified phosphorylation sites on FREE1, mediated by FER, to non-phosphorylable residues results in reduced nucleus localization of FREE1 and increased hypersensitivity to ABA. Our data also show that these six phosphorylation sites are likely involved in regulating plant survival under salt stress. Collectively, our study not only unveils an additional function of FER in attenuating ABA signaling in the nucleus but also provides a possible insight into the role of the RALF1-FER-FREE1 module in coordinating plant growth and salt stress tolerance.

中文翻译：

---

RALF1-FERONIA 复合物磷酸化 FREE1 以减弱幼苗建立过程中的脱落酸信号传导


受体样激酶 FERONIA （FER） 及其配体快速碱化因子 1 （RALF1） 肽在调节应激反应中起着至关重要的作用，包括其参与调节脱落酸 （ABA） 信号传导。FER 已被证明可激活细胞质中的 ABA 不敏感 2 （ABI2），导致 ABA 信号传导受到抑制。然而，它对 ABA 反应中细胞核事件的调节仍不清楚。FREE1 被确定为真核生物中运输所需的内体分选复合物 （ESCRT） 的植物特异性组分，是 ABA 信号传导中的重要负调节因子。在这项研究中，我们阐明了在 RALF1 处理后，FER 磷酸化 FREE1，促进 FREE1 蛋白在拟南芥 （Arabidopsis thaliana） 细胞核中的积累。因此，FREE1 通过抑制 ABA 反应基因的表达来抑制 ABA 敏感性。由 FER 介导的 FREE1 上已鉴定的 6 个磷酸化位点突变为不可磷酸化残基，导致 FREE1 的细胞核定位减少，对 ABA 的超敏反应增加。我们的数据还表明，这 6 个磷酸化位点可能参与调节盐胁迫下植物的存活。总的来说，我们的研究不仅揭示了 FER 在减弱细胞核中 ABA 信号传导方面的附加功能，而且还为 RALF1-FER-FREE1 模块在协调植物生长和耐盐胁迫中的作用提供了可能的见解。