Philip-Hollingsworth S, Dazzo F B, Hollingsworth R I
Department of Microbiology, Michigan State University, East Lansing 48824, USA.
J Lipid Res. 1997 Jun;38(6):1229-41.
Rhizobium chitolipooligosaccharides (CLOSs) are heterogeneous fatty acylated N-acetyl glucosamine oligomers with variations in both the polar (hydrophilic) oligosaccharide head group and the non-polar (hydrophobic) fatty acyl chain. They trigger root hair deformation and cortical cell divisions in legume roots during development of the nitrogen-fixing root-nodule symbiosis. It has been proposed that only certain unique molecular species of CLOSs made by a particular rhizobia can elicit these responses on the corresponding legume host, suggesting that receptor-mediated perception of CLOSs serves as a basis of symbiotic specificity. We evaluated the relative symbiotic importance of the hydrophilic and hydrophobic structural domains of CLOSs by comparing the biological activities of CLOSs from wild type R. leguminosarum bv. trifolii ANU843 with that of various synthetic analogs. These tests were performed in axenic bioassays on the compatible symbiotic host, white clover (Trifolium repens) and the incompatible non-host legume, alfalfa (Medicago sativa). Fluorochrome-tagged derivatives of the native CLOSs and the analogs were also prepared in order to evaluate the uptake and localization patterns of these molecules within host root cells. The results indicate a direct link between uptake and biological activities of Rhizobium CLOSs on legume roots. The smallest CLOS analog taken up and biologically active on white clover and alfalfa was a N-fatty acylglucosamine, without an essential requirement of oligomerization, fatty N-acyl unsaturation, or acetate/sulfate functionalization. This suggests that N-fattyacylglucosamine is the common minimum structure required and sufficient for uptake and biological activity of CLOS glycolipids in these legumes, and that the various specific modifications of its polar head group and hydrophobic tail modulate its inherent ability to further express these activities, thus influencing which legumes are capable of responding to CLOSs rather than dictating their biological activities per se.
根瘤菌壳寡糖（CLOSs）是一类异质性的脂肪酰化N - 乙酰葡糖胺寡聚物，其极性（亲水性）寡糖头部基团和非极性（疏水性）脂肪酰链均存在差异。在固氮根瘤共生体发育过程中，它们会引发豆科植物根中的根毛变形和皮层细胞分裂。有人提出，只有特定根瘤菌产生的某些独特分子种类的CLOSs才能在相应的豆科宿主上引发这些反应，这表明受体介导的CLOSs感知是共生特异性的基础。我们通过比较野生型三叶草根瘤菌（Rhizobium leguminosarum bv. trifolii）ANU843产生的CLOSs与各种合成类似物的生物活性，评估了CLOSs亲水性和疏水性结构域的相对共生重要性。这些测试在无菌生物测定中对兼容的共生宿主白三叶草（Trifolium repens）和不兼容的非宿主豆科植物苜蓿（Medicago sativa）进行。还制备了天然CLOSs及其类似物的荧光染料标记衍生物，以评估这些分子在宿主根细胞内的摄取和定位模式。结果表明根瘤菌CLOSs在豆科植物根上的摄取与生物活性之间存在直接联系。在白三叶草和苜蓿上摄取并具有生物活性的最小CLOS类似物是N - 脂肪酰葡糖胺，对寡聚化、脂肪N - 酰基不饱和或乙酸盐/硫酸盐功能化没有基本要求。这表明N - 脂肪酰葡糖胺是这些豆科植物中CLOS糖脂摄取和生物活性所需的共同最小结构且足够，并且其极性头部基团和疏水尾部的各种特定修饰调节了其进一步表达这些活性的固有能力，从而影响哪些豆科植物能够对CLOSs做出反应，而不是决定其本身的生物活性。
