Schwember Andrés R, Schulze Joachim, Del Pozo Alejandro, Cabeza Ricardo A
Departamento de Ciencias Vegetales, Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Santiago 306-22, Chile.
Department of Crop Science, Section for Plant Nutrition and Crop Physiology, Faculty of Agriculture, University of Goettingen, Carl-Sprengel-Weg 1, 37075 Goettingen, Germany.
Plants (Basel). 2019 Sep 6;8(9):333. doi: 10.3390/plants8090333.
In most legume nodules, the di-nitrogen (N)-fixing rhizobia are present as organelle-like structures inside their root host cells. Many processes operate and interact within the symbiotic relationship between plants and nodules, including nitrogen (N)/carbon (C) metabolisms, oxygen flow through nodules, oxidative stress, and phosphorous (P) levels. These processes, which influence the regulation of N fixation and are finely tuned on a whole-plant basis, are extensively reviewed in this paper. The carbonic anhydrase (CA)-phosphoenolpyruvate carboxylase (PEPC)-malate dehydrogenase (MDH) is a key pathway inside nodules involved in this regulation, and malate seems to play a crucial role in many aspects of symbiotic N fixation control. How legumes specifically sense N-status and how this stimulates all of the regulatory factors are key issues for understanding N fixation regulation on a whole-plant basis. This must be thoroughly studied in the future since there is no unifying theory that explains all of the aspects involved in regulating N fixation rates to date. Finally, high-throughput functional genomics and molecular tools (i.e., miRNAs) are currently very valuable for the identification of many regulatory elements that are good candidates for accurately dissecting the particular N fixation control mechanisms associated with physiological responses to abiotic stresses. In combination with existing information, utilizing these abundant genetic molecular tools will enable us to identify the specific mechanisms underlying the regulation of N fixation.
在大多数豆科植物根瘤中，固氮根瘤菌以细胞器样结构存在于其宿主根细胞内。植物与根瘤之间的共生关系中存在许多相互作用的过程，包括氮（N）/碳（C）代谢、氧气在根瘤中的流动、氧化应激和磷（P）水平。本文对这些影响固氮调节且在整株植物水平上受到精细调控的过程进行了广泛综述。碳酸酐酶（CA）-磷酸烯醇式丙酮酸羧化酶（PEPC）-苹果酸脱氢酶（MDH）是根瘤内参与该调节的关键途径，苹果酸似乎在共生固氮控制的许多方面发挥着关键作用。豆科植物如何特异性感知氮状态以及这如何刺激所有调节因子，是从整株植物水平理解固氮调节的关键问题。由于目前尚无统一理论能解释迄今为止固氮速率调节所涉及的所有方面，因此未来必须对此进行深入研究。最后，高通量功能基因组学和分子工具（即微小RNA）目前对于鉴定许多调节元件非常有价值，这些元件是准确剖析与非生物胁迫生理反应相关的特定固氮控制机制的良好候选者。结合现有信息，利用这些丰富的遗传分子工具将使我们能够确定固氮调节的具体机制。
