Role of Exopolysaccharides in the Sinorhizobium Meliloti/Alfalfa Symbiosis

University Of Texas At Dallas, Richardson TX

Investigators

Abstract

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.