The FERONIA receptor kinase is required for high humidity responses in Arabidopsis

High humidity greatly influences plant growth and development and triggers adaptive physiological responses such as leaf hyponasty (elongation of leaf petiole and upward leaf movement). A recent study identified Cyclic Nucleotide-Gated Ion Channels 2 and 4 (CNGC2/4)-mediated Ca2+ influx and Calmodulin Binding Transcription Activators 2 and 3 (CAMTA2/3)-mediated transcription as essential for high humidity response in Arabidopsis, but the upstream regulators that control these pathways remain unknown. Here, we show that the receptor-like kinase FERONIA and its co-receptor LORELEI-LIKE GPI-ANCHORED PROTEIN1 (LLG1) are required for a large portion of high humidity-associated Arabidopsis transcriptomic changes, including CNGC2, CAMTA -regulated genes, and cell wall remodeling genes, and for high humidity-induced leaf hyponasty. High humidity triggers a previously uncharacterized petiole-localized Ca ²⁺ waves that precede hyponastic leaf movement. The petiole-localized Ca ²⁺ signals were significantly altered in the fer-4 mutant. Thus, FERONIA is a key regulator of plant responses to extracellular high humidity.