Department of Molecular Biology and Genetics, Aarhus University, 8000 Aarhus C, Denmark.
Proc Natl Acad Sci U S A. 2024 Nov 12;121(46):e2405671121. doi: 10.1073/pnas.2405671121. Epub 2024 Nov 4.
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 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.
根瘤共生的建立始于植物 LysM 受体激酶 NFR1 和 NFR5 对细菌 Nod 因子配体的感知。启动共生途径的受体信号取决于 NFR1 的激酶活性，而催化失活的 NFR5 假激酶的信号机制尚不清楚。在这里，我们呈现了信号功能完整的 NFR5 细胞内域的晶体结构，包括跨膜区和假激酶结构域。跨膜区结构定义良好，形成两个α-螺旋，αA 和 αA'，其中包含一个暴露的疏水性基序。我们证明了这个“跨膜基序”促进了 NFR5-NFR5 和 NFR1-NFR5 的相互作用，对于共生信号转导是必不可少的。保守性分析表明，跨膜基序存在于整个 NFR5 型受体中，并且对于大麦 RLK10 的共生信号转导也是必需的，这表明该基序在植物-微生物共生中具有保守和更广泛的功能。
