The establishment of the symbiotic interaction between rhizobia and legumes involves the Nod factor signaling pathway. Nod factor recognition occurs through two plant receptors, NFR1 and NFR5. However, the signal transduction mechanisms downstream of NFR1-NFR5-mediated Nod factor perception remain largely unknown. Here, we report that a small guanosine triphosphatase (GTPase), GmROP9, and a guanine nucleotide exchange factor, GmGEF2, are involved in the soybean-rhizobium symbiosis. We show that GmNFR1α phosphorylates GmGEF2a at its N-terminal S86, which stimulates guanosine diphosphate (GDP)-to-GTP exchange to activate GmROP9 and that the active form of GmROP9 can associate with both GmNFR1α and GmNFR5α. We further show that a scaffold protein, GmRACK1, interacts with active GmROP9 and contributes to root nodule symbiosis. Collectively, our results highlight the symbiotic role of GmROP9-GmRACK1 and support the hypothesis that rhizobial signals promote the formation of a protein complex comprising GmNFR1, GmNFR5, GmROP9, and GmRACK1 for symbiotic signal transduction in soybean.

根瘤菌和豆科植物之间共生相互作用的建立涉及Nod因子信号通路。 Nod 因子识别通过两种植物受体 NFR1 和 NFR5 进行。然而，NFR1-NFR5 介导的 Nod 因子感知下游的信号转导机制仍然很大程度上未知。在这里，我们报道了一种小鸟苷三磷酸酶（GTPase）GmROP9 和鸟嘌呤核苷酸交换因子 GmGEF2 参与大豆-根瘤菌共生。我们发现，GmNFR1α 在其 N 端 S86 处磷酸化 GmGEF2a，从而刺激二磷酸鸟苷 (GDP) 与 GTP 的交换，从而激活 GmROP9，并且 GmROP9 的活性形式可以与 GmNFR1α 和 GmNFR5α 结合。我们进一步表明支架蛋白 GmRACK1 与活性 G​​mROP9 相互作用并有助于根瘤共生。总的来说，我们的结果强调了 GmROP9-GmRACK1 的共生作用，并支持这样的假设：根瘤菌信号促进包含 GmNFR1、GmNFR5、GmROP9 和 GmRACK1 的蛋白质复合物的形成，用于大豆中的共生信号转导。