Host Recognition in the Rhizobium-Soybean Symbiosis

Polar binding of Rhizobium japonicum to roots and root hairs of Glycine soja (L.) Sieb. and Zucc. is specifically inhibited by d-galactose and N-acetyl-d-galactosamine, haptens of Glycine max seed lectin. A protein, immunologically cross-reactive with the G. max seed lectin, is present in G. soja seed extracts. Peptide mapping of the purified G. max and G. soja lectins indicates that the two are similar in structure. Soybean lectin can be localized on the surface of both G. max and G. soja roots by indirect immunolatex techniques. These observations indicate that the Rhizobium-binding lectin, previously isolated from seeds, also is present on the root surface-the site of the initial steps in the infection. This lectin is capable of binding Rhizobium japonicum to the root.