Controlling growth and development in a spatiotemporal manner is crucial for all multicellular organisms. Misregulation of the underlying signaling pathways is often associated with excessive tissue proliferation, leading to oncogenesis in animals and humans. Similarly, organ development and size control are important in plants, and understanding the underlying mechanisms may aid future biotechnological approaches to increase crop yield.

An important family of proteins regulating growth and development are plasma membrane-localized receptor kinases (RKs), which represent a major family of signal-transducing proteins conserved across kingdoms [1]. Their function is mainly linked to their ability to bind extracellular ligands, such as peptides or other small molecules, with subsequent transmembrane activation of downstream signaling pathways, resulting in an appropriate cellular output.

In recent years, RKs belonging to the Catharanthus roseus receptor-like kinase 1-like (CrRLK1L) family emerged as important regulators of plant reproduction, responses to the environment, growth, and development [2]. In Arabidopsis, the first discovered and best described CrRLK1L is FERONIA (FER), which was initially found to be required for pollen tube perception in the female reproductive organ, the pistil, and later found to be involved in a plethora of responses, including root hair growth, cell elongation, hormone responses, and plant immunity [2]. Yet for a long time, it was unclear how FER is activated, as no ligands were described. Recent research has shown that FER (and related CrRLK1Ls) perceive peptide ligands belonging to the family of rapid alkalinization factors (RALFs) [3–7]. There are at least 36 genes encoding for RALF peptides in the genome of Arabidopsis thaliana, raising the possibility that FER and related RKs fulfil a multitude of functions by perceiving tissue- and/or context-specific RALF peptides, some of which also modulate FER and related proteins in an antagonistic manner [4,5]. The first described FER ligand was the root-specific RALF1 [3], and the last years have provided significant insights into the signal transduction pathways activated in response to its perception. The small glycosylphosphatidylinositol (GPI)-anchored proteins LORELEI (LRE) and the related LRE-like GPI-anchored protein 1 (LLG1) are required for FER plasma membrane localization in a tissue-specific manner and are discussed as potential RALF coreceptor proteins [8]. The receptor-like cytoplasmic kinase (RLCK) RPM1-interacting protein kinase (RIPK) and FER mutually phosphorylate each other to regulate cell growth in roots [9]. Furthermore, FER was shown to activate rho of plants (ROP) signaling to positively regulate auxin-dependent root hair growth, which in turn is counteracted by abscisic acid (ABA)-induced FER phosphorylation via inhibition of the A-type protein phosphatase 2C (PP2C) ABA insensitive 2 (ABI2) [10–12]. Despite the advances in our understanding of early FER-dependent responses, it remains largely unknown how this central regulatory RK regulates downstream cellular responses beyond the plasma membrane, including transcriptional or translational reprogramming.

In this issue of PLOS Biology, Li and colleagues [13] identify the plant ortholog of the mammalian DNA/RNA-binding protein ERBB3 binding protein 1 (EBP1) as an interactor of FER and potentially other CrRLK1L family members (Fig 1A and 1B). The authors show that EBP1 mRNA translation (not transcription) is enhanced after RALF1 perception in a FER-dependent manner, resulting in elevated EBP1 protein levels (Fig 1A). Subsequently, EBP1 is translocated to the nucleus, a response that is dependent on FER-mediated phosphorylation (Fig 1B). Here, EBP1 associates with RALF1 responsive genes and regulates their transcription. Genetically, EBP1 largely serves as a negative regulator of RALF1 signaling.