Corning Chloe, Dolatmoradi Marjan, Tran Tina H, Stacey Gary, Szente Lajos, Samarah Laith Z, Vertes Akos
Department of Chemistry, The George Washington University, Washington, DC, 20052, USA.
Divisions of Plant Sciences and Technology, C. S. Bond Life Sciences Center, University of Missouri, Columbia, MO, 65211, USA.
Mater Today Bio. 2025 Apr 18;32:101776. doi: 10.1016/j.mtbio.2025.101776. eCollection 2025 Jun.
In the symbiotic relationship of legumes and rhizobia, disaccharides, mostly sucrose, are produced by the plant and provided as energy and carbon sources for the bacteria. The microbes, in turn, store these carbohydrates as acyclic oligohexoses to buffer fluctuations in supply. Simultaneously, cyclic oligohexoses (β-glucans) of varying sizes and structures are synthesized by nitrogen-fixing soil bacteria both in free living form and in legume root nodules. In the bacteroids, transformed from strain USDA110 in soybean () root nodules, glucose units are attached by glycosidic bonds and are known to contain degrees of polymerization with 10 ≤ ≤ 13 repeat units in branched cyclic structures. Whereas cyclic β-glucans (CβGs) are thought to facilitate bacterial adaptation and legume-rhizobia symbiosis, information on their ring sizes, branching from the ring structures, and their spatial distributions within the nodules is scarce. Here we demonstrate that using mass spectrometry (MS), based on matrix-assisted laser desorption ionization (MALDI) and laser desorption ionization (LDI) from emerging silicon nanopost array (NAPA) nanophotonic platforms, the presence of a wider array of potentially cyclic oligohexoses can be discovered with degrees of polymerization in the 2 ≤ ≤ 14 residue range. On the low end of the oligomer size distribution, the cyclic nature of CY with < 10 can be increasingly questioned based on the large strain such macrocycles would exhibit and the DP control during the CβG synthesis by the glucan phosphorylase involved in their synthesis. At the same time, acyclic oligohexoses with a degree of polymerization of 2 ≤ ≤ 13 were also detected. Tandem MS with collision induced dissociation (CID) indicated that the cyclic structure with = 12 contained a branching residue. It detached from the macrocycle at lower collision energies (70 instrument units), whereas the rings themselves fragmented at higher energies (90 instrument units). We also prove that the spatial distributions of acyclic and cyclic oligohexoses in the nodules can be captured by MS imaging (MSI) based on MALDI and NAPA-LDI. The acyclic species were more abundant in the infection zone, whereas the cyclic oligohexoses appeared more concentrated in the inner cortex and in the root vasculature. At some locations, possibly in the vascular bundles surrounding the nodule and traversing the root, the cyclic oligohexoses were especially abundant. The distributions of acyclic oligohexoses were also mapped in the nodule sections. These linear or branching molecules were abundant in the infection zone, where the cyclic oligohexoses were less concentrated or absent.
在豆科植物与根瘤菌的共生关系中，植物产生双糖（主要是蔗糖），并将其作为细菌的能量和碳源提供给细菌。反过来，微生物将这些碳水化合物储存为无环寡己糖，以缓冲供应的波动。同时，不同大小和结构的环寡己糖（β-葡聚糖）由固氮土壤细菌在自由生活形式和豆科植物根瘤中合成。在大豆根瘤中由USDA110菌株转化而来的类菌体中，葡萄糖单元通过糖苷键连接，已知在分支环状结构中含有聚合度为10≤ ≤13个重复单元。虽然环β-葡聚糖（CβGs）被认为有助于细菌适应和豆科植物-根瘤菌共生，但关于它们的环大小、环结构分支以及它们在根瘤内的空间分布的信息却很少。在这里，我们证明，使用基于新兴硅纳米柱阵列（NAPA）纳米光子平台的基质辅助激光解吸电离（MALDI）和激光解吸电离（LDI）的质谱（MS），可以发现聚合度在2≤ ≤14个残基范围内的更多种类的潜在环寡己糖。在寡聚物大小分布的低端，基于<10的CY的大环性质以及参与其合成的葡聚糖磷酸化酶在CβG合成过程中的DP控制，<10的CY的环状性质越来越受到质疑。同时，还检测到聚合度为2≤ ≤13的无环寡己糖。具有碰撞诱导解离（CID）的串联质谱表明， = 12的环状结构含有一个分支残基。它在较低的碰撞能量（70仪器单位）下从大环上脱离，而环本身在较高能量（90仪器单位）下断裂。我们还证明，基于MALDI和NAPA-LDI的质谱成像（MSI）可以捕获大豆根瘤中无环和环寡己糖的空间分布。无环物种在感染区更为丰富，而环寡己糖似乎更集中在内皮层和根脉管系统中。在某些位置，可能在围绕根瘤并穿过根的维管束中，环寡己糖特别丰富。无环寡己糖的分布也在根瘤切片中进行了映射。这些线性或分支分子在感染区丰富，而环寡己糖在该区域浓度较低或不存在。
