Role of Exopolysaccharides in the Sinorhizobium Meliloti/Alfalfa Symbiosis

所有栖息地都依靠细菌固定大气中的氮或合成氮肥来提供固定氮的供应。一些植物已经与固氮菌建立了共生关系，因此可以从大气中获得大量的氮。紫花苜蓿/紫花苜蓿根瘤共生关系的一个很好的例子是紫花苜蓿产生的胞外多糖在根瘤共生中发挥着特殊的作用，特别是在根瘤入侵的水平上。紫花苜蓿胞外多糖突变体的结构特异性和少量外源胞外多糖是成功挽救其入侵缺陷所必需的，这表明低分子量胞外多糖在入侵过程中起着信号分子的作用。这项工作旨在了解导致植物对胞外多糖反应的信号机制，以及检测或识别胞外多糖信号存在的可能的植物受体的鉴定和特征。对这些问题的回答将有助于更好地理解共生伙伴之间的信号机制，并可能为寡糖在其他生物系统中作为信号分子的可能用途提供见解。

All habitats rely on the bacterial fixation of atmospheric nitrogen or on the synthetic production of nitrogen fertilizers for providing a supply of fixed nitrogen. Some plants have established symbiosis with nitrogen-fixing bacteria, and therefore can obtain much of their nitrogen from the atmosphere. One prime example of this relationship is the alfalfa/Sinorhizobium meliloti symbiosis.It is increasingly evident that exopolysaccharides produced by S. meliloti play specific roles in the development of the root nodule symbiosis between the bacteria and legumes, particularly at the level of nodule invasion. The structural specificity and the small amounts of exogenous exopolysaccharide necessary to successfully rescue the invasion deficiency of S. meliloti exopolysaccharide mutants, suggest that low molecular weight exopolysaccharides act as signaling molecules during the invasion process. This work aims to understand the signaling mechanisms that lead to the plant's response to exopolysaccharides, and the identification and characterization of the putative plant receptors that detect or recognize the presence of the exopolysaccharide signals.The answers to these and related questions will lead to a greater understanding of the signaling mechanisms between symbiotic partners and may also provide insights into the possible uses of oligosaccharides as signaling molecules in other biological systems.