Symbiotic nodules comprise two classes, indeterminate and determinate, defined by the presence/absence of apical meristem and developmental zonation. Why meristem and zonation are absent from determinate nodules remains unclear. Here, we define cell types in developing soybean nodules, highlighting the undifferentiated infection zones and differentiated nitrogen-fixation zones. Auxin governs infection zone maintenance. GRETCHEN HAGEN 3 (GH3) enzymes deactivate auxin by conjugation and promote cell differentiation. gh3 mutants increased undifferentiated cells and enlarged infection zones. The central symbiosis-transcription factor NIN2a activates GH3.1 to reduce auxin levels and facilitates cell differentiation. High auxin promotes NIN2a protein accumulation and enhances signaling, further deactivating auxin and depleting infection zones. Our findings shed light on the NIN2a-GH3-auxin module that drives soybean nodule cell differentiation. This study challenges our understanding of determinate nodule development and proposes that the regulation of nodule zonation offers valuable insights into broader mechanisms of cell differentiation across plant species.

共生结节包括两类，不确定和确定，由顶端分生组织和发育带的存在/不存在定义。为什么确定的结节中没有分生组织和带状结构仍不清楚。在这里，我们定义了发育大豆根瘤中的细胞类型，突出了未分化的感染区和分化的固氮区。生长素控制感染区的维护。GRETCHEN HAGEN 3 （GH3） 酶通过结合使生长素失活并促进细胞分化。GH3 突变体增加了未分化细胞并扩大了感染区。中枢共生转录因子 NIN2a 激活 GH3.1 以降低生长素水平并促进细胞分化。高生长素促进 NIN2a 蛋白积累并增强信号传导，进一步使生长素失活并消耗感染区。我们的研究结果揭示了驱动大豆根瘤细胞分化的 NIN2a-GH3-生长素模块。这项研究挑战了我们对确定性根瘤发展的理解，并提出根瘤分区的调节为跨植物物种细胞分化的更广泛机制提供了有价值的见解。