Plant receptor kinases (RKs) are critical for transmembrane signalling involved in various biological processes including plant immunity. MALE DISCOVERER1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) is a unique RK that recognizes a family of immunomodulatory peptides called SERINE-RICH ENDOGENOUS PEPTIDEs (SCOOPs) and activates pattern-triggered immunity responses. However, the precise mechanisms underlying SCOOP recognition and activation of MIK2 remain poorly understood. Here we present the cryogenic electron microscopy structure of a ternary complex consisting of the extracellular leucine-rich repeat (LRR) of MIK2 (MIK2LRR), SCOOP12 and the extracellular LRR of the co-receptor BAK1 (BAK1LRR) at a resolution of 3.34 Å. The structure reveals that a DNHH motif in MIK2LRR plays a critical role in specifically recognizing the highly conserved SxS motif of SCOOP12. Furthermore, the structure demonstrates that N-glycans at MIK2LRR^Asn410 directly interact with the N-terminal capping region of BAK1LRR. Mutation of the glycosylation site, MIK2LRR^N410D, completely abolishes the SCOOP12-independent interaction between MIK2LRR and BAK1LRR and substantially impairs the assembly of the MIK2LRR–SCOOP12–BAK1LRR complex. Supporting the biological relevance of N410-glycosylation, MIK2^N410D substantially compromises SCOOP12-triggered immune responses in plants. Collectively, these findings elucidate the mechanism underlying the loose specificity of SCOOP recognition by MIK2 and reveal an unprecedented mechanism by which N-glycosylation modification of LRR-RK promotes receptor activation.

植物受体激酶 （RK） 对于参与各种生物过程（包括植物免疫）的跨膜信号传导至关重要。雄性 DISCOVERER1 相互作用受体样激酶 2 （MIK2） 是一种独特的 RK，可识别称为富含丝氨酸的内源性肽 （SCOOP） 的免疫调节肽家族，并激活模式触发的免疫反应。然而，SCOOP 识别和激活 MIK2 的确切机制仍然知之甚少。在这里，我们展示了由 MIK2 （MIK2LRR SCOOP12） 的细胞外富含亮氨酸重复序列 （LRR） 和共受体 BAK1 （BAK1LRR） 的细胞外 LRR 组成的三元复合物的低温电子显微镜结构，分辨率为 3.34 Å。该结构表明，MIK2LRR 中的 DNHH 基序在特异性识别 SCOOP12 高度保守的 SxS 基序方面起着关键作用。此外，该结构表明^Asn410 MIK2LRR 位点的 N 糖直接与 BAK1LRR 的 N 端加帽区相互作用。糖基化位点 MIK2LRR^N410D 的突变完全消除了 MIK2LRR 和 BAK1LRR 之间的不依赖SCOOP12的相互作用，并严重损害了 MIK2LRR-SCOOP12-BAK1LRR 复合物的组装。MIK2^N410D 支持 N410-糖基化的生物学相关性，严重损害植物中 SCOOP12 触发的免疫反应。总的来说，这些发现阐明了 MIK2 识别 SCOOP 的松散特异性的潜在机制，并揭示了 LRR-RK 的 N-糖基化修饰促进受体激活的前所未有的机制。