Role of Exopolysaccharides in the Sinorhizobium Meliloti/Alfalfa Symbiosis

所有的栖息地都依赖于细菌对大气氮的固定或氮肥的合成生产来提供固定氮的供应。有些植物已经与固氮细菌建立了共生关系，因此可以从大气中获得大部分氮。这种关系的一个主要例子是紫花苜蓿/Sinorhizobium meliloti。越来越多的证据表明，S. meliloti产生的外多糖在细菌与豆科植物的根瘤共生发展中起着特定的作用，特别是在根瘤侵袭水平上。结构特异性和少量外源胞外多糖可以成功地挽救S. meliloti胞外多糖突变体的入侵缺陷，这表明低分子量的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外多糖反应的信号机制，以及检测或识别外多糖信号存在的假定植物受体的鉴定和表征。这些问题和相关问题的答案将有助于更好地理解共生伙伴之间的信号机制，也可能为低聚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.