Signorelli Santiago, Sainz Martha, Tabares-da Rosa Sofía, Monza Jorge
Laboratorio de Bioquímica, Departamento de Biología Vegetal, Facultad de Agronomía, Universidad de la República, Montevideo, Uruguay.
The School of Molecular Sciences, Faculty of Science, The University of Western Australia, Crawley, WA, Australia.
Front Plant Sci. 2020 Jun 3;11:521. doi: 10.3389/fpls.2020.00521. eCollection 2020.
The legume-rhizobia symbiosis is an important process in agriculture because it allows the biological nitrogen fixation (BNF) which contributes to increasing the levels of nitrogen in the soil. Nitric oxide (⋅NO) is a small free radical molecule having diverse signaling roles in plants. Here we present and discuss evidence showing the role of ⋅NO during different stages of the legume-rhizobia interaction such as recognition, infection, nodule development, and nodule senescence. Although the mechanisms by which ⋅NO modulates this interaction are not fully understood, we discuss potential mechanisms including its interaction with cytokinin, auxin, and abscisic acid signaling pathways. In matures nodules, a more active metabolism of ⋅NO has been reported and both the plant and rhizobia participate in ⋅NO production and scavenging. Although ⋅NO has been shown to induce the expression of genes coding for NITROGENASE, controlling the levels of ⋅NO in mature nodules seems to be crucial as ⋅NO was shown to be a potent inhibitor of NITROGENASE activity, to induce nodule senescence, and reduce nitrogen assimilation. In this sense, LEGHEMOGLOBINS (Lbs) were shown to play an important role in the scavenging of ⋅NO and reactive nitrogen species (RNS), potentially more relevant in senescent nodules. Even though ⋅NO can reduce NITROGENASE activity, most reports have linked ⋅NO to positive effects on BNF. This can relate mainly to the regulation of the spatiotemporal distribution of ⋅NO which favors some effects over others. Another plausible explanation for this observation is that the negative effect of ⋅NO requires its direct interaction with NITROGENASE, whereas the positive effect of ⋅NO is related to its signaling function, which results in an amplifier effect. In the near future, it would be interesting to explore the role of environmental stress-induced ⋅NO in BNF.
豆科植物与根瘤菌的共生关系是农业中的一个重要过程，因为它能实现生物固氮（BNF），有助于提高土壤中的氮含量。一氧化氮（·NO）是一种小自由基分子，在植物中具有多种信号传导作用。在此，我们展示并讨论了证据，表明·NO在豆科植物与根瘤菌相互作用的不同阶段，如识别、感染、根瘤发育和根瘤衰老过程中所起的作用。尽管·NO调节这种相互作用的机制尚未完全了解，但我们讨论了潜在的机制，包括其与细胞分裂素、生长素和脱落酸信号通路的相互作用。据报道，在成熟根瘤中，·NO的代谢更为活跃，植物和根瘤菌都参与·NO的产生和清除。尽管·NO已被证明能诱导编码固氮酶的基因表达，但控制成熟根瘤中·NO的水平似乎至关重要，因为·NO被证明是固氮酶活性的有效抑制剂，能诱导根瘤衰老并降低氮同化作用。从这个意义上说，豆血红蛋白（Lbs）在清除·NO和活性氮物质（RNS）方面发挥了重要作用，这在衰老根瘤中可能更为相关。尽管·NO会降低固氮酶活性，但大多数报告都将·NO与对生物固氮的积极影响联系起来。这主要可能与·NO的时空分布调节有关，这种调节有利于某些影响而非其他影响。对此观察结果的另一个合理的解释是，·NO的负面影响需要其与固氮酶直接相互作用，而·NO的积极影响与其信号传导功能有关，这会产生放大效应。在不久的将来，探索环境胁迫诱导的·NO在生物固氮中的作用将是很有趣的。
