Establishment of root nodule symbiosis is initiated by the perception of bacterial Nod factor ligands by the plant LysM receptor kinases NFR1 and NFR5. Receptor signaling initiating the symbiotic pathway depends on the kinase activity of NFR1, while the signaling mechanism of the catalytically inactive NFR5 pseudokinase is unknown. Here, we present the crystal structure of the signaling-competent Lotus japonicus NFR5 intracellular domain, comprising the juxtamembrane region and pseudokinase domain. The juxtamembrane region is structurally well defined and forms two α-helices, αA and αA′, which contain an exposed hydrophobic motif. We demonstrate that this “juxtamembrane motif” promotes NFR5–NFR5 and NFR1–NFR5 interactions and is essential for symbiotic signaling. Conservation analysis reveals that the juxtamembrane motif is present throughout NFR5-type receptors and is required for symbiosis signaling from barley RLK10, suggesting a conserved and broader function for this motif in plant–microbe symbioses.

中文翻译：

---

植物 NFR5 受体中保守的近膜基序对于根瘤共生至关重要


根瘤共生的建立是由植物 LysM 受体激酶 NFR1 和 NFR5 对细菌 Nod 因子配体的感知启动的。启动共生途径的受体信号传导取决于 NFR1 的激酶活性，而催化失活的 NFR5 假激酶的信号传导机制尚不清楚。在这里，我们展示了具有信号能力的 Lotus japonicus NFR5 细胞内结构域的晶体结构，包括近膜区域和假激酶结构域。近膜区域结构明确，形成两个α螺旋，αA 和 αA′，其中包含暴露的疏水基序。我们证明这种“并联膜基序”促进 NFR5-NFR5 和 NFR1-NFR5 相互作用，并且对于共生信号传导至关重要。保守分析显示，近膜基序存在于整个 NFR5 型受体中，并且是大麦 RLK10 共生信号转导所必需的，表明该基序在植物-微生物共生中具有保守且更广泛的功能。