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bioRxiv · 10.64898/2026.01.03.697504

Rapid sensing and relaying of cellular hyperosmotic-stress signals via RAF-SnRK2 core condensates

Liu, G.·Lin, Z.·Lin, G.·Wang, X.·Liu, X.·Lang, Z.·Zhu, J.-K.·Wang, P.
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Abstract

Hyperosmolarity caused by drought, high salinity, or cold stress inhibits plant growth and crop productivity1,2. A conserved protein-kinase cascade of cytosolic B-RAFs and SnRK2s is rapidly activated upon osmotic stresses to initiate downstream adaptive responses, which represents one of the fastest known responses to osmotic stress in plants3-8. How the kinase cascade is activated by osmotic stress is unknown. Here, we show that Arabidopsis B4 subgroup RAFs have intrinsically disordered regions and directly sense both ionic and non-ionic hyperosmolarity by reversible condensation. B4-RAFs recruit and co-condense with subclass-I SnRK2s to phosphorylate and turn on SnRK2s, evading the non-condensable inhibitory A-clade PP2C phosphatases. This straightforward osmosensing and relaying module can be fully reconstituted in E. coli by co-expressing three components or in solution in a test tube using recombinant proteins. Our findings identify B-RAFs as the chief cellular osmosensors that detect low water potential by co-condensation, forming a signal hub with SnRK2s to orchestrate adaptive responses in plants, and represent an evolutionarily conserved osmosensing mechanism across kingdoms.

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Liu, G., Lin, Z., Lin, G., Wang, X., Liu, X., Lang, Z., Zhu, J.-K., Wang, P.. 2026-01-03. Rapid sensing and relaying of cellular hyperosmotic-stress signals via RAF-SnRK2 core condensates. https://doi.org/10.64898/2026.01.03.697504

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