Mechanism Of Protein Synthesis Regulated By Receptor Like Kinase FERONIA In Response To RALF1 Signal In Arabidopsis Root

Protein is the component of cells and the main carrier of life activities.Protein synthesis in eukaryotes is the basic process of cell activities and needs to be highly coordinated with the process of other cells.During growth,the surface of cells expands by adding new material to the membrane or cell wall.Simultaneously,the synthesis of new cytoplasmic content(e.g.,proteins)increases the cell's volume.Polarized cell growth,a process that extends an enormous length relative to its width,is crucial to the development or survival of the organism.In animals,plants and fungi,there are distinct examples of cells that exhibit polarized growth,including neuronal axon,pollen tube and root hairs,fungal hyphae.Accumulating evidence suggests that protein synthesis in a spatiotemporally controlled fashion could regulate cell size and shape in different organisms.However,there is limited evidence to explain how extracellular signals may regulate translation with spatial precision through the protein synthesis machinery in eukaryotic cells.Plant RAPID ALKALINIZATION FACTORS(RALFs)are secreted peptides that function as extracellular signals and bind to Catharanthus roseus RECEPTOR-LIKE KINASES 1-LIKE(Cr RLK1L)family members such as FERONIA(FER),RALF1–FER complexes are central regulators of plant cell size and shape that allow plants to respond to environmental changes.RALF1-FER complex promotes ERBB3–BINDING PROTEIN 1(EBP1)m RNA translation,and triggers the nuclear accumulation of EBP1.Thus,it was suggested that RALF1–FER complex may regulate protein synthesis and thereby control cell size,however,in plant cell signal transduction studies,few studies have clarified how external signals regulate RNA processes(e.g.,alternative splicing,translation and stability).Unveiling the definite molecular mechanism of RALF1-FER regulating protein synthesis is critical to demonstrate how the plant cells respond to environmental signals by controlling protein synthesis.The main conclusions as below.(1)RALF1-FER promotes the protein synthesis of root hair related genes.(2)eIF4E1 physically interacts with FER at plasma membrane(PM).We found FER kinase could phosphorylate eIF4E1 protein.Using mass spectrometry,five eIF4E1 phosphorylation sites regulated by FER were identified.The interaction of FER and eIF4E1 is regulated by their reciprocal phosphorylation.The complete phosphorylation of eIF4E1 reduces its affinity toward FER.(3)The Tyr¹¹⁸and Thr¹⁴⁰of eIF4E1 is directly related to m RNA binding.eIF4E1phosphorylation status is crutial for its m RNA cap binding ability.(4)eIF4E1 was revealed working in Arabidopsis root hair polar growth,rosette size,pavement cell shape,and RALF1 response.eIF4E1 abundance and phosphorylation status control cell size and shape downstream of FER.(5)RALF1,FER and eIF4E1 show clear polar localization of both of the encoded fusion proteins during the initiation,and rapid growth stages of root hair development RALF1 affects the polar localization of eIF4E1 via recruitment based on the FER–eIF4E1 phosphorylation at the PM.FER–eIF4E1 influences the polar localization of ROP2.(6)RALF1 promoter contained a DNA sequence with a typical Root hair-specific cis-element(RHE)region.RSL4 indeed bound to the RHE sequence in vitro.RALF1treatment promotes the association between the RSL4 protein and the enrichment of RHE sequences in the RALF1 promoter.High levels of RSL4 suppress RALF1 m RNA expression,thus negatively impacting the RALF1–FER signaling pathway.