SUGAR-BINDING ACTIVITY OF PEA LECTIN EXPRESSED IN WHITE CLOVER HAIRY ROOTS

Introduction of the pea (Pisum sativum L.) lectin (PSL) gene into whit e clover (Trifolium repens L.) hairy roots facilitates nodulation by t he nitrogen-fixing bacterium Rhizobium leguminosarum biovar viciae, wh ich normally nodulates pea and not white clover (C.L. Diaz, L.S. Melch ers, P.J.J. Hooykaas, B.J.J. Lugtenberg, and J.W. Kijne [1989] Nature 338: 579-581). Here, we show that PSL is functionally expressed in tra nsgenic white clover hairy roots transformed with the PSL gene. PSL co uld be isolated from these roots by affinity chromatography. Immunoana lysis of PSL showed the presence of polypeptides corresponding to the PSL precursor and its beta subunits. In addition, we developed a highl y sensitive localization technique based on specific binding of a glyc an moiety of rat IgE to PSL. Similar to the situation in pea roots, PS L appeared to be localized on the external cell surface of elongated e pidermal cells and on the tips of emerging and growing root hairs of t ransgenic white clover hairy roots. PSL was not observed on normal whi te clover roots and on hairy roots without the PSL gene. These results show that (a) in transgenic white clover hairy roots, PSL is correctl y processed and targeted to root cells susceptible to rhizobial infect ion, and (b) like in pea roots, PSL is surface bound with at least one of its two sugar-binding sites available for (rhizobial) ligands.