TAILIEUCHUNG - Báo cáo khoa học: Surface polysaccharide involvement in establishing the rhizobium–legume symbiosis

When the rhizosphere is nitrogen-starved, legumes and rhizobia (soil bacteria)enter intoa symbiosis that enables the fixation of atmospheric dinitrogen. This implies a complex chemical dialogue between partners and drastic changes on both plant roots and bacteria. Several recent works pointed out the importance of rhizobial surface polysaccharides in the establishing of the highly specific symbiosis between symbionts. Exopolysaccharides appear tobe essential for the early infection process. | Eur. J. Biochem. 270 1365-1380 2003 FEBS 2003 doi REVIEW ARTICLE Surface polysaccharide involvement in establishing the rhizobium-legume symbiosis Nicolas Fraysse Francois Couderc and Véréna Poinsot Laboratoire des IMRCP UMR5623 UPSỊCNRS 118 route de Narbonne F-31062 Toulouse France When the rhizosphere is nitrogen-starved legumes and rhizobia soil bacteria enter into a symbiosis that enables the fixation of atmospheric dinitrogen. This implies a complex chemical dialogue between partners and drastic changes on both plant roots and bacteria. Several recent works pointed out the importance of rhizobial surface polysaccharides in the establishing of the highly specific symbiosis between symbionts. Exopolysaccharides appear to be essential for the early infection process. Lipopolysaccharides exhibit specific roles in the later stages of the nodulation processes such as the penetration of the infection thread into the cortical cells or the setting up of the nitrogen-fixing phenotype. More generally even if active at different steps of the establishing of the symbiosis all the polysaccharide classes seem to be involved in complex processes of plant defense inhibition that allow plant root invasion. Their chemistry is important for structural recognition as well as for physico-chemical properties. Keywords polysaccharide rhizobium symbiosis role junction infection. Introduction Soil bacteria collectively known as rhizobia have the property of interacting with legume roots in nitrogen-starved environments to form nodules where atmospheric dinitrogen can be fixed. The establishment of this symbiosis is based on a complex molecular dialogue starting with secretion of flavonoids by the host plant roots. At least one of the roles of flavonoids is to activate the products of rhizobial regulatory nodD genes 1 2 . The interaction between the two partners seems to begin at a distance in the rhizosphere even before rhizobia bind to the legume root

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