Updated publication reference for PubMed record(s): 32001690. Osmotic stress associated with drought, salinity and cold is a major factor limits plant productivity. A few signaling factors have been identified in the sensing or early signaling of osmotic stress. SNF1-related protein kinase 2 (SnRK2) are quickly activated by osmotic stress and the snrk2 decuple are sensitive to hyperosmolality and defective in osmotic stress induced cellular responses. Mechanically activated ion channels Hyperosmolality-induced Ca2+ increases (OSCA) may involve in the sorbitol-evoked Ca2+ increase. However, how plant senses osmotic stress and quickly activates SnRK2s is still unclear. Here we report osmotic stress active protein kinases (OKs), a subfamily of Raf protein kinases, involved in early signaling of osmotic stress in plant. OKs quickly and specifically activated by multiple hyperosmolality, but not by phytohormone abscisic acid or cold stress. The high order mutants of oks were hypertensive to hyperosmolality. In addition, OKs physically interact with and phosphorylate SnRK2s in vivo and in vitro, and this phosphorylation is required for activation of SnRK2s upon osmotic stress. Our results indicated the OKs-SnRK2s kinase cascade in plant osmotic stress responses, which provide a potential molecular machinery mediates osmotic stress signaling in plant.