LIPM, Université de Toulouse, INRAE, CNRS, INSA, Castanet-Tolosan, France
LIPM, Université de Toulouse, INRAE, CNRS, INSA, Castanet-Tolosan, France.
Appl Environ Microbiol. 2020 Dec 17;87(1). doi: 10.1128/AEM.02210-20.
Rhizobia are bacteria which can either live as free organisms in the soil or interact with plants of the legume family with, as a result, the formation of root organs called nodules in which differentiated endosymbiotic bacteria fix atmospheric nitrogen to the plant's benefit. In both lifestyles, rhizobia are exposed to nitric oxide (NO) which can be perceived as a signaling or toxic molecule. NO can act at the transcriptional level but can also modify proteins by -nitrosylation of cysteine or nitration of tyrosine residues. However, only a few molecular targets of NO have been described in bacteria and none of them have been characterized in rhizobia. Here, we examined tyrosine nitration of proteins induced by NO. We found three tyrosine-nitrated proteins in grown under free-living conditions, in response to an NO donor. Two nitroproteins were identified by mass spectrometry and correspond to flagellins A and B. We showed that one of the nitratable tyrosines is essential to flagellin function in motility. Rhizobia are found as free-living bacteria in the soil or in interaction with plants and are exposed to nitric oxide (NO) in both environments. NO is known to have many effects on animals, plants, and bacteria where only a few molecular targets of NO have been described so far. We identified flagellin A and B by mass spectrometry as tyrosine-nitrated proteins in We also showed that one of the nitratable tyrosines is essential to flagellin function in motility. The results enhanced our understanding of NO effects on rhizobia. Identification of bacterial flagellin nitration opens a new possible role of NO in plant-microbe interactions.
根瘤菌是一类既能在土壤中自由生活，又能与豆科植物相互作用的细菌，其结果是在根器官中形成被称为根瘤的分化内共生细菌，这些根瘤可以将大气氮固定到植物身上，为植物提供好处。在这两种生活方式中，根瘤菌都会接触到一氧化氮（NO），NO 可以被视为一种信号或毒性分子。NO 可以在转录水平上发挥作用，但也可以通过半胱氨酸的亚硝基化或酪氨酸残基的硝化来修饰蛋白质。然而，在细菌中只描述了少数几个 NO 的分子靶标，而且在根瘤菌中没有一个被表征。在这里，我们研究了 NO 诱导的蛋白质酪氨酸硝化。我们发现，在自由生活条件下生长的 中，有三种蛋白质发生了酪氨酸硝化，这是对一氧化氮供体的反应。通过质谱鉴定出两种硝化蛋白，它们分别对应于鞭毛蛋白 A 和 B。我们表明，可硝化的酪氨酸之一对鞭毛蛋白的运动功能是必需的。根瘤菌在土壤中以自由生活的细菌形式存在，或与植物相互作用，并在这两种环境中接触到一氧化氮（NO）。众所周知，NO 对动物、植物和细菌有许多影响，但到目前为止，只有少数几个 NO 的分子靶标被描述过。我们通过质谱鉴定出 flagellin A 和 B 是 中的酪氨酸硝化蛋白。我们还表明，可硝化的酪氨酸之一对鞭毛蛋白的运动功能是必需的。研究结果增强了我们对 NO 对根瘤菌影响的理解。细菌鞭毛蛋白硝化的鉴定为 NO 在植物-微生物相互作用中的新作用开辟了可能。
