Identification of COSR1 and COSR2 as hypoosmotic-activated Ca2+-permeable channels that are critical for submergence tolerance and post-drought recovery in Arabidopsis.

Drought recovery and submergence confer hypoosmotic stress that disrupts plant cellular homeostasis and compromises growth and survival. Although calcium signaling serves as a central hub for plant adaptation to osmotic perturbations, the molecular mechanisms underlying hypoosmotic responses remain poorly understood. In this study, we identified COSR1 (Calcium-permeable Osmotic Stress Response 1) and its homolog COSR2 as Ca2+-permeable channels that are activated by hypoosmotic stimuli. Genetic analyses revealed that COSR1 plays a predominant role, with COSR2 serving a secondary compensatory role, as the cosr1 cosr2 double mutant exhibited substantially more severe phenotypes than either single mutant under post-drought recovery and submergence. Calcium imaging further demonstrated that COSR1 and COSR2 collectively mediate the second spike of hypoosmotic-induced Ca2+ influx, which is closely associated with TCH2/TCH4 induction and stress tolerance. Together, our work establishes that COSR1 and COSR2 are key components of the hypoosmotic-responsive signaling machinery that translates post-drought recovery and submergence-induced osmotic stress into Ca2+ signals, providing novel targets for improving crop resilience.