Abstract：
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 mis-expression 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.
摘要：
在营养缺乏期间，植物可以调整他们的发展策略，以最大限度地提高他们的生存机会。这种发育的可塑性是由荷尔蒙调节支撑的，调节环境线索和发展产出之间的关系。在豆类中，与固氮细菌（根瘤菌）的内共生是向植物提供铵形式的氮的关键适应。根瘤菌位于称为结节的侧根来源的器官中，该结节维持有利于这些细菌中固氮酶的环境。几种植物激素对调节结节的形成很重要，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生物传感器确定结节器官形成过程中生物活性GA的细胞位置和功能，苜蓿中的GIBBERELLIN感知传感器2。我们发现内源性生物活性GA在结节原基部位局部积累，在皮质细胞层中急剧增加，持续通过细胞分裂并在成熟的结节分生组织中保持积累。我们展示,通过抑制GA积累的GA分解代谢酶的错误表达，GA是结节生长和发育的正调节剂。此外，通过生物合成基因表达的扰动增加或减少GA可以增加或减少结节的大小，分别。这是侧根形成的独特之处，共享共同器官发生调节因子的发展计划。通过显示结节同一性基因诱导并维持适当结节形成所需的GA积累，我们将GA与更广泛的基因调控程序联系起来。
