During nutrient scarcity, plants can adapt their developmental strategy to maximize their chance of survival. Such plasticity in development is underpinned by hormonal regulation, which mediates the relationship between environmental cues and developmental outputs. In legumes, endosymbiosis with nitrogen-fixing bacteria (rhizobia) is a key adaptation for supplying the plant with nitrogen in the form of ammonium. Rhizobia are housed in lateral root-derived organs termed nodules that maintain an environment conducive to Nitrogenase in these bacteria. Several phytohormones are important for regulating the formation of nodules, with both positive and negative roles proposed for gibberellin (GA). In this study, we determine the cellular location and function of bioactive GA during nodule organogenesis using a genetically encoded second-generation GA biosensor, GIBBERELLIN PERCEPTION SENSOR 2 in Medicago truncatula. We find endogenous bioactive GA accumulates locally at the site of nodule primordia, increasing dramatically in the cortical cell layers, persisting through cell divisions, and maintaining accumulation in the mature nodule meristem. We show, through misexpression of GA-catabolic enzymes that suppress GA accumulation, that GA acts as a positive regulator of nodule growth and development. Furthermore, increasing or decreasing GA through perturbation of biosynthesis gene expression can increase or decrease the size of nodules, respectively. This is unique from lateral root formation, a developmental program that shares common organogenesis regulators. We link GA to a wider gene regulatory program by showing that nodule-identity genes induce and sustain GA accumulation necessary for proper nodule formation.

中文翻译：

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使用赤霉素感知传感器 2 在苜蓿苜荆外侧器官中揭示控制结瘤的赤霉素动力学


在养分稀缺期间，植物可以调整其发育策略以最大限度地提高其生存机会。这种发育中的可塑性以荷尔蒙调节为基础，荷尔蒙调节介导环境线索与发育产出之间的关系。在豆类中，与固氮细菌 （根瘤菌） 的内共生是以铵态氮形式为植物提供氮的关键适应。根瘤菌位于称为根瘤的侧根来源器官中，这些器官维持着有利于这些细菌中固氮酶的环境。几种植物激素对于调节根瘤的形成很重要，赤霉素 （GA） 具有积极和消极的作用。在这项研究中，我们使用基因编码的第二代 GA 生物传感器、苜蓿中的赤霉素感知传感器 2 确定了生物活性 GA 在根瘤器官发生过程中的细胞位置和功能。我们发现内源性生物活性 GA 在根瘤原基位点局部积累，在皮质细胞层中急剧增加，通过细胞分裂持续存在，并在成熟根瘤分生组织中维持积累。我们通过抑制 GA 积累的 GA 分解代谢酶的错误表达表明，GA 是结节生长和发育的正调节因子。此外，通过扰动生物合成基因表达增加或减少 GA 可以分别增加或减少结节的大小。这与侧根形成不同，侧根形成是一种共享共同器官发生调节因子的发育程序。我们通过证明结节同一基因诱导和维持正确结节形成所必需的 GA 积累，将 GA 与更广泛的基因调控计划联系起来。