Sugar-Binding Activity of Pea Lectin Expressed in White Clover Hairy Roots

Abstract

Dénarié et al., 1992). Nodulation is regulated by a two-way exchange of plant and bacterial signal molecules (Fisher and Long, 1992;Spaink et al., 1993). Signal exchange begins in the rhizosphere. Rhizobia sense flavonoids secreted by seeds and by the host plant root, which activate the constitutively expressed nodD gene product (reviewed by Schlaman et al., 1992). This step is a determinant of host plant specificity in some Rhizobium-host plant combinations (Horvath et al., 1987; Spaink et al., 1987). Transcription of structural nod genes is under the control of NodD and results in production and secretion of specific lipochitin oligosaccharides (Nod factors), which act as host plant-specific inducers of nodule morphogenesis (reviewed by Dénarié and Cullimore, 1993;Spaink et al., 1993). Most probably, Nod factors constitute the primary determinants of host-plant specificity of nodulation.Root lectins are plant factors involved in nodulation. Lectins are nonenzymatic sugar-binding (g1yco)proteins characterized by sugar-binding specificity. For example, root PSL is Glc/Man specific (Díaz et al., 1990) and white clover root lectin is 2-deoxyglucose specific (Sherwood et al., 1984). In general, the interaction between RI uiciae and white clover does not proceed beyond root hair curling, and these bacteria are not able to penetrate host plant cells by infection thread formation (Yao and Vincent, 1969;Djordjevic et al., 1986;Huang et al., 1993). However, RI viciae is able to induce infection thread formation and nodulation in a significant percentage of white clover plants with roots transformed with the psl gene, as reported by Díaz et al. (1989Díaz et al. ( , 1995. This heterologous nodulation does not take place when a psl mutant, which encodes a non-sugar-binding protein, is used for transformation of white clover roots (Van Eijsden et al., 1992. These results strongly suggest that (a) PSL is functionally expressed in transgenic white clover roots, (b) conservation of the sugar-binding activity of PSL is necessary for infection of white clover by RI viciae, and (c) root lectin helps to break a host plant-specific barrier for nodulation. The relationship between Nod factor recognition by host plants and Rhizobium recognition by host lectin is not yet clear.PSL is an ellipsoidal, nonglycosylated dimeric lectin with two sugar-binding sites, each located near the top of two identical monomers (Einspahr et al., 1988). PSL is encoded by a single gene (Gatehouse et al., 1987;Kaminski et al., 1987) and is synthesized as a single translation product, a prolectin with a molecular mass of 28 kD. Posttranslational modifications result in a protein that dissociates into two p subunits (18 kD each) and two 01 subunits (6 kD each, Higgins et al., 1983)

Glucomannan-Mediated Attachment ofRhizobium leguminosarumto Pea Root Hairs Is Required for Competitive Nodule Infection

“…This is consistent with the prediction (41) that the glucomannan is required for lectin-mediated attachment to root hairs. At alkaline pH, the root lectin which binds the glucomannan is released from the root hairs, and this probably prevents glucomannan-mediated attachment (16,41). An alternative mechanism of attachment has been proposed to occur at alkaline pH, a mechanism mediated via bacterially made rhicadhesin (56).…”

“…Under slightly alkaline conditions the lectin is released from pea root hairs, significantly reducing this type of attachment (16). However, rhicadhesin, a calcium-binding protein produced by all tested members of the Rhizobiaceae (56), can facilitate attachment to root hairs under neutral or alkaline conditions (41).…”

Role of Glycosylation in Conformational Stability, Activity, Macromolecular Interaction and Immunogenicity of Recombinant Human Factor VIII

“…It has been reported that carbohydrates in glycoproteins are important for protein folding (12,13,17), stability (11,18), macromolecular interactions, and activity (19)(20)(21). Furthermore, alteration of glycosylation can affect the immunogenicity of therapeutic proteins as it has been demonstrated in the case of interferon beta (22,23).…”

Infection and Invasion of Roots by Symbiotic, Nitrogen-Fixing Rhizobia during Nodulation of Temperate Legumes

“…These lectins localize to root hair tips and are thought to help convey host-symbiont specificity by binding simultaneously to the plant cell wall and to saccharide moieties on the surfaces of compatible bacteria (41,43,79). A series of experiments in which a variety of transgenic plants expressed lectins from other species of legumes has shown that the presence of heterologous lectins often allows transgenic plants to respond to symbionts that are usually noncompatible, provided that the heterologous lectin can bind to the noncompatible bacteria and provided that the noncompatible bacteria make the proper Nod factor (42,79,171,172).…”