Specificity and kinetics of oligosaccharide recognition by RSL,a fucose-binding lectin from the plant pathogen Ralstoniasolanacearum.

Ralstonia solanacearum is a worldwide distributed plant aggressive pathogen which causes lethal wilt in many crops. Its extracts contain a fucose-binding lectin that has been recently purified and characterized [1]. Its 90 amino acid sequence contains two repeating domains, with strong similarity to the fucose-binding lectin of the mushroom Aleuria aurantia (AAL), which is also a soil inhabitant. Surface plasmon resonance experiments demonstrate that the lectin binds strongly to fragments of fucose-containing xyloglucan polysaccharide purified from plant cell walls. This binding can diversely be inhibited by fucose and fucose-containing oligosaccharides. Best inhibition was obtained with oligosaccharides containing an aFuc(1-2)Gal terminal disaccharide, particularly XG9 (Glc4 Xyl3 Gal Fuc) which is a structurally well determined plant oligosaccharide that has previously been demonstrated to have biological activity in plants [2]. Our results are in agreement with the assumption that RSL plays a role in binding of the bacterium to specific oligosaccharides that are present in the primary root hairs cell wall of the host plant.