Université Côte d'Azur, INRA, CNRS, ISA, France.
J Exp Bot. 2019 Aug 29;70(17):4505-4520. doi: 10.1093/jxb/erz159.
Interactions between legumes and rhizobia lead to the establishment of a symbiotic relationship characterized by the formation of a new organ, the nodule, which facilitates the fixation of atmospheric nitrogen (N2) by nitrogenase through the creation of a hypoxic environment. Significant amounts of nitric oxide (NO) accumulate at different stages of nodule development, suggesting that NO performs specific signaling and/or metabolic functions during symbiosis. NO, which regulates nodule gene expression, accumulates to high levels in hypoxic nodules. NO accumulation is considered to assist energy metabolism within the hypoxic environment of the nodule via a phytoglobin-NO-mediated respiration process. NO is a potent inhibitor of the activity of nitrogenase and other plant and bacterial enzymes, acting as a developmental signal in the induction of nodule senescence. Hence, key questions concern the relative importance of the signaling and metabolic functions of NO versus its toxic action and how NO levels are regulated to be compatible with nitrogen fixation functions. This review analyses these paradoxical roles of NO at various stages of symbiosis, and highlights the role of plant phytoglobins and bacterial hemoproteins in the control of NO accumulation.
豆科植物与根瘤菌之间的相互作用导致共生关系的建立，其特征是形成一个新的器官——根瘤，通过创造一个低氧环境，固氮酶可以利用根瘤固定大气中的氮气（N2）。在根瘤发育的不同阶段会积累大量的一氧化氮（NO），这表明在共生过程中，NO 执行特定的信号转导和/或代谢功能。NO 调节根瘤基因表达，在低氧根瘤中积累到很高的水平。NO 积累被认为通过植物血球蛋白-NO 介导的呼吸过程来协助根瘤低氧环境中的能量代谢。NO 是氮酶和其他植物和细菌酶活性的强抑制剂，作为诱导根瘤衰老的发育信号。因此，关键问题是 NO 的信号转导和代谢功能相对于其毒性作用的相对重要性，以及如何调节 NO 水平使其与固氮功能兼容。本综述分析了 NO 在共生的各个阶段的这些矛盾作用，并强调了植物血球蛋白和细菌血红素蛋白在控制 NO 积累中的作用。
