Perraki, ArtemisDeFalco, Thomas ADerbyshire, PaulAvila, JulianSere, DavidSklenar, JanQi, XingyunStransfeld, LenaSchwessinger, BenjaminKadota, YasuhiroMacho, Alberto PJiang, ShushuZipfel, Cyril2021-11-230028-0836http://hdl.handle.net/1885/251928Multicellular organisms use cell-surface receptor kinases to sense and process extracellular signals. Many plant receptor kinases are activated by the formation of ligand-induced complexes with shape-complementary co-receptors1. The best-characterized co-receptor is BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED KINASE 1 (BAK1), which associates with numerous leucine-rich repeat receptor kinases (LRR-RKs) to control immunity, growth and development2. Here we report key regulatory events that control the function of BAK1 and, more generally, LRR-RKs. Through a combination of phosphoproteomics and targeted mutagenesis, we identified conserved phosphosites that are required for the immune function of BAK1 in Arabidopsis thaliana. Notably, these phosphosites are not required for BAK1-dependent brassinosteroid-regulated growth. In addition to revealing a critical role for the phosphorylation of the BAK1 C-terminal tail, we identified a conserved tyrosine phosphosite that may be required for the function of the majority of Arabidopsis LRR-RKs, and which separates them into two distinct functional classes based on the presence or absence of this tyrosine. Our results suggest a phosphocode-based dichotomy of BAK1 function in plant signalling, and provide insights into receptor kinase activation that have broad implications for our understanding of how plants respond to their changing environment.This work was supported by the Gatsby Charitable Foundation and the European Research Council (grant ‘PHOSPHinnATE’) (C.Z.); the Gordon and Betty Moore Foundation (grant GBMF3035) and the Howard Hughes Medical Institute (K.U.T.); the European Molecular Biology Organization (EMBO-LTFs 100-2017 to T.A.D. and 225-2015 to S.J.); the RIKEN Special Postdoctoral Research Fellowship, the JSPS Excellent Young Researcher Overseas Visit Program, and the Uehara Memorial Foundation (Y.K.); and the JIC/TSL PhD Rotation Program (B.S.)application/pdfen-AU© 2018 Springer Nature Limited201810.1038/s41586-018-0471-x2020-11-23