[Nature] The calcium-permeable channel OSCA1.3 regulates plant stomatal immunity

Perception of biotic and abiotic stresses often leads to stomatal closure in plants^1,2. Rapid influx of calcium ions (Ca²⁺) across the plasma membrane plays an important role in this response, but the identity of Ca²⁺ channels involved has remained elusive^3,4. Here, we report that the Arabidopsis thaliana Ca²⁺-permeable channel OSCA1.3 controls stomatal closure during immunity. OSCA1.3 is rapidly phosphorylated upon perception of pathogen-associated molecular patterns (PAMPs). Biochemical and quantitative phospho-proteomics analyses reveal that the immune receptor-associated cytosolic kinase BIK1 interacts with and phosphorylates the N-terminal cytosolic loop of OSCA1.3 within minutes of treatment with the peptidic PAMP flg22 derived from bacterial flagellin. Genetic and electrophysiological data reveal that OSCA1.3 is permeable to Ca²⁺, and that BIK1-mediated phosphorylation on its N-terminus increases this channel activity. Importantly, OSCA1.3 and its phosphorylation by BIK1 are critical for stomatal closure during immunity. Notably, OSCA1.3 does not regulate stomatal closure upon perception of abscisic acid - a plant hormone associated with abiotic stresses. Our study thus identifies a long sought-after plant Ca²⁺ channel and its activation mechanisms underlying stomatal closure during immune signaling, and suggests specificity in Ca²⁺ influx mechanisms in response to different stresses.