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.