FERONIA as a Signal Integration Hub: Reconciling Growth–Defense Trade-offs Across Environmental Contexts and Crop Species

Plants continuously integrate developmental, hormonal and environmental signals to optimise growth, reproduction and survival under changing environmental conditions. A central component of this regulatory network is FERONIA (FER), a plasma membrane-associated receptor-like kinase belonging to the Catharanthus roseus receptor-like kinase 1-like (CrRLK1L) family. Increasing evidence identifies FER as a multifunctional signalling hub that coordinates cell expansion, cell-wall integrity, reactive oxygen species (ROS) homeostasis, phytohormone signalling and plant immunity. However, the mechanisms through which FER reconciles growth–defense trade-offs, particularly across agriculturally important species, remain incompletely understood. This review critically synthesises current knowledge of FER-mediated signalling, with emphasis on the RALF–FER–LLG receptor complex, phytohormonal interactions, cell-wall sensing and immune regulation. It also compares experimental data on rice (Oryza sativa), tomato (Solanum lycopersicum), wheat (Triticum aestivum), apple (Malus domestica) and poplar (Populus spp.), identifying conserved signalling features and species-specific functional divergence. Rice studies show that mutations in specific FERONIA-like receptors can increase blast resistance without significant growth penalty, while tomato studies show a molecular mechanism involving the FER-dependent phosphorylation of MYB63 and regulation of lignin deposition. In wheat, a pathogen-derived RALF mimic can down-regulate host immunity and inhibit cell growth, and recent research in apple and poplar has uncovered other links between FER-associated signalling, drought adaptation, salinity tolerance and disease susceptibility. The results taken together contradict the notion that FER acts in a universal growth promoting or defence-suppressing manner. Rather, its biological products seem to be influenced by the nature of the ligand, the structure of the receptor, the tissue specificity, the developmental stage and the environmental context.We identify limited field validation, incomplete mechanistic characterisation of crop homologues and insufficient understanding of receptor–ligand specificity as major translational bottlenecks. Finally, we propose a comparative research framework integrating genome editing, phosphoproteomics, molecular breeding and multi-environment field evaluation to exploit FER-associated signalling for improved crop resilience and yield stability.