The FERONIA receptor kinase is required for high humidity responses in Arabidopsis
High humidity greatly influences plant growth and development by triggering adaptive physiological responses such as leaf hyponasty. Recent studies identified CNGC2/4-mediated Ca2+ influx and CAMTA2/3-mediated transcription as essential for this process, but the upstream regulators that control these pathways remain unknown. Here, we show that the receptor-like kinase FERONIA (FER) is required for Arabidopsis adaptation to high humidity. Transcriptomic profiling revealed rapid induction of CNGC2, CAMTA targets, and pectin remodeling genes in wild-type plants but not in fer-4 loss of function mutants. A targeted mutant screen confirmed that FER and its co-receptor LORELEI-LIKE GPI-ANCHORED PROTEIN1 (LLG1) are essential for humidity-induced hyponasty. Whole-plant Ca²? imaging demonstrated that high humidity triggers conserved cytosolic Ca²? elevations across species, including petiole-localized Ca²? waves in Arabidopsis that precede hyponastic movement by ~2 h. These signals were significantly attenuated in fer-4, providing a mechanistic explanation for its transcriptional and physiological defects. Together, our findings identify FERONIA as a key upstream component of a sensing mechanism linking extracellular high humidity to Ca²? signaling, cell wall remodeling, and adaptive leaf movement. Overall design: RNA-seq profliing of Arabidopsis plants (Col-0 and the fer-4 mutant) exposed to the high humidity conditions after 0 min, 15 min, 60 min, 24 hours and 6 days of ambient and high humidity conditions,