Pa. Balatti et al., RHIZOBIUM SP, NGR234 CONTAINS A FUNCTIONAL COPY OF THE SOYBEAN CULTIVAR SPECIFICITY LOCUS, NOLXWBTUV, Molecular plant-microbe interactions, 8(5), 1995, pp. 693-699
Rhizobium sp, NGR234, a broad host range nitrogen-fixing symbiont of m
any legumes, is closely allied to Rhizobium fredii, but there are conf
licting reports of its ability to nodulate soybean, the normal host of
R. fredii, We evaluated the symbiotic interaction of NGR234 with 89 s
oybean cultivars and detected only disorganized structures, which had
central vascular connections and lacked bacteroids. NGR234 contains no
lXWBTUV, a locus responsible for cultivar-specific nodulation of soybe
an by R. fredii USDA257, We cloned the NGR234 locus as an 8.0-kb EcoRI
fragment and found that its restriction map differs from that of the
corresponding fragment from USDA257 at only two sites, RNA dot blot an
alysis indicated that the NGR234 locus is expressed in response to fla
vonoid signals, This observation was confirmed by probing Western blot
s with polyclonal antibodies directed against NolX of USDA257 and by m
onitoring levels of expression of a fusion between the nolX allele of
NGR234 and lacZ, Histochemical observations with the gene fusion docum
ented that nolX is expressed by rhizobia in the rhizosphere of soybean
roots and in infection threads and mature nodules of cowpea.