Departamento de Biotecnología-Biología Vegetal, Escuela Técnica Superior de Ingeniería Agronómica, Alimentaria y de Biosistemas, Universidad Politécnica de Madrid, Madrid, Spain.
Metallomics. 2019 Apr 17;11(4):735-755. doi: 10.1039/c8mt00372f.
A group of bacteria known as rhizobia are key players in symbiotic nitrogen fixation (SNF) in partnership with legumes. After a molecular exchange, the bacteria end surrounded by a plant membrane forming symbiosomes, organelle-like structures, where they differentiate to bacteroids and fix nitrogen. This symbiotic process is highly dependent on dynamic nutrient exchanges between the partners. Among these are transition metals (TM) participating as inorganic and organic cofactors of fundamental enzymes. While the understanding of how plant transporters facilitate TMs to the very near environment of the bacteroid is expanding, our knowledge on how bacteroid transporters integrate to TM homeostasis mechanisms in the plant host is still limited. This is significantly relevant considering the low solubility and scarcity of TMs in soils, and the in crescendo gradient of TM bioavailability rhizobia faces during the infection and bacteroid differentiation processes. In the present work, we review the main metal transporter families found in rhizobia, their role in free-living conditions and, when known, in symbiosis. We focus on discussing those transporters which could play a significant role in TM-dependent biochemical and physiological processes in the bacteroid, thus paving the way towards an optimized SNF.
一组被称为根瘤菌的细菌是与豆科植物共生固氮（SNF）的关键参与者。在分子交换后，细菌最终被植物膜包围形成共生体，这是一种类似细胞器的结构，在共生体中它们分化为类菌体并固定氮。这种共生过程高度依赖于伙伴之间的动态营养交换。其中包括作为基本酶的无机和有机辅因子的过渡金属（TM）。虽然植物转运蛋白如何将 TMs 运送到类菌体的非常近的环境的理解正在扩大，但我们对类菌体转运蛋白如何整合到植物宿主中的 TM 稳态机制的了解仍然有限。考虑到土壤中 TMs 的低溶解度和稀缺性，以及根瘤菌在感染和类菌体分化过程中面临的 TM 生物利用度递增梯度，这一点非常重要。在本工作中，我们综述了在根瘤菌中发现的主要金属转运蛋白家族，它们在自由生活条件下的作用，以及在共生条件下的作用（如果已知的话）。我们重点讨论了那些在类菌体中可能在 TM 依赖的生化和生理过程中发挥重要作用的转运蛋白，从而为优化 SNF 铺平道路。
