Santana Margarida M, Gonzalez Juan M, Cruz Cristina
Centro de Ecologia, Evolução e Alterações Ambientais (cE3c), Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal.
Instituto de Recursos Naturales y Agrobiología, Consejo Superior de Investigaciones Científicas (CSIC), Sevilla, Spain.
Front Microbiol. 2017 Oct 10;8:1947. doi: 10.3389/fmicb.2017.01947. eCollection 2017.
Many publications highlight the importance of nitric oxide (NO) in plant-bacteria interactions, either in the promotion of health and plant growth or in pathogenesis. However, the role of NO in the signaling between bacteria and plants and in the fate of their interaction, as well as the reconstruction of their interactive evolution, remains largely unknown. Despite the complexity of the evolution of life on Earth, we explore the hypothesis that denitrification and aerobic respiration were responsible for local NO accumulation, which triggered primordial antagonistic biotic interactions, namely the first phytopathogenic interactions. N-oxides, including NO, could globally accumulate via lightning synthesis in the early anoxic ocean and constitute pools for the evolution of denitrification, considered an early step of the biological nitrogen cycle. Interestingly, a common evolution may be proposed for components of denitrification and aerobic respiration pathways, namely for NO and oxygen reductases, a theory compatible with the presence of low amounts of oxygen before the great oxygenation event (GOE), which was generated by Cyanobacteria. During GOE, the increase in oxygen caused the decrease of Earth's temperature and the consequent increase of oxygen dissolution and availability, making aerobic respiration an increasingly dominant trait of the expanding mesophilic lifestyle. Horizontal gene transfer was certainly important in the joint expansion of mesophily and aerobic respiration. First denitrification steps lead to NO formation through nitrite reductase activity, and NO may further accumulate when oxygen binds NO reductase, resulting in denitrification blockage. The consequent transient NO surplus in an oxic niche could have been a key factor for a successful outcome of an early denitrifying prokaryote able to scavenge oxygen by NO/oxygen reductase or by an independent heterotrophic aerobic respiration pathway. In fact, NO surplus could result in toxicity causing "the first disease" in oxygen-producing Cyanobacteria. We inspected in bacteria the presence of sequences similar to the NO-producing nitrite reductase gene of , an extreme thermophilic aerobe of the group, which constitutes an ancient lineage related to Cyanobacteria. analysis revealed the relationship between the presence of genes and phytopathogenicity in Gram-negative bacteria.
许多出版物都强调了一氧化氮（NO）在植物与细菌相互作用中的重要性，无论是在促进植物健康和生长方面，还是在发病机制中。然而，NO在细菌与植物之间的信号传导以及它们相互作用的结果，以及它们相互作用进化的重建方面所起的作用，在很大程度上仍然未知。尽管地球生命进化过程复杂，但我们探讨了这样一种假说：反硝化作用和好氧呼吸导致了局部NO积累，从而引发了原始的拮抗生物相互作用，即最初的植物病原相互作用。包括NO在内的N-氧化物可能在早期缺氧海洋中通过闪电合成而全球积累，并构成反硝化作用进化的库，反硝化作用被认为是生物氮循环的早期步骤。有趣的是，可以提出反硝化作用和好氧呼吸途径的组成部分存在共同进化，即NO和氧还原酶，这一理论与大氧化事件（GOE）之前低含量氧气的存在相符合，大氧化事件是由蓝细菌产生的。在大氧化事件期间，氧气的增加导致地球温度下降，进而导致氧气溶解和可用性增加，使好氧呼吸成为不断扩展的中温生物生活方式中越来越占主导地位的特征。水平基因转移在中温生物和好氧呼吸的共同扩展中肯定很重要。反硝化作用的第一步通过亚硝酸还原酶活性导致NO形成，当氧气与NO还原酶结合时，NO可能会进一步积累，导致反硝化作用受阻。因此，有氧生态位中随之而来的短暂NO过剩可能是早期能够通过NO/氧还原酶或独立的异养有氧呼吸途径清除氧气的反硝化原核生物成功的关键因素。事实上，NO过剩可能导致毒性，在产氧蓝细菌中引发“第一种疾病”。我们在细菌中检测了与嗜热栖热放线菌（一种与蓝细菌相关的古老谱系的极端嗜热需氧菌）的产生NO的亚硝酸还原酶基因相似的序列的存在。分析揭示了革兰氏阴性细菌中该基因的存在与植物致病性之间的关系。
