Host Recognition in the Rhizobium-Soybean Symbiosis

Abstract

(2,3,10,15,32). In the soybean system, a 120,000 dalton glycoprotein with specificity for D-galactose and N-acetyl-D-galactosamine binds specifically to infective strains of Rhizobium japonicum (2,3,(19)(20)(21). This lectin is found in seeds, leaves, stems, and roots of several varieties of Glycine max (23,26), although it appears to be absent or in very low quantity in a few varieties (26,29). Even with all of the evidence indicating that the lectin specifically binds to R. japonicum, there has been little direct evidence showing that this lectin actually binds the bacteria to the root. In only one legume system, that of white clover, has direct evidence been presented that a lectin binds the bacterium to the root (9, 10, 12).In that case, the lectin was localized at the site of infection. A hapten of the clover lectin, 2-deoxyglucose, specifically prevents binding of Rhizobium tr#folii to clover roots (9, 1 1). Similar studies to those performed with clover have not been done with soybeans chiefly because of the difficulty of adapting light microscopic studies to a large plant.Here, we overcame the difficulties of using a large plant such as G. max by using Glycine soja, a small-seeded soybean. The nodulation specificities of G. max and G. soja are very similar (6 The Rhizobium inoculum was grown in yeast extract-mannitol broth (30) at 30 C. The plant nutrient solution used (W. Leps, unpublished results) was as follows: 2 mm CaSO4.2H20; 5 mM K2SO4; 5 mm NaH2PO4. H20; 40 AM ethylene diaminetetraacetic acid ferric salt; 0.5 /IM CoCl2-6H20; 0.5 iM MgSO4.7H20; and I ml/l micronutrient solution (30). The pH of the PNS was adjusted to 7.0 with NaOH after autoclaving. Plants were grown at light intensity of 300 tiE/M2.* swith an 18-h photoperiod at 23-25C.Assay for Binding of Bacteria to Roots. G. soja seeds were sterilized by swirling them for 10 min in Clorox (The Clorox Co., Oakland, Calif.). The seeds were rinsed with sterile distilled H20 and scarified by soaking them in concentrated H2SO4 for 5 min. The seeds were rinsed with sterile H20 and soaked for an additional 10 min in 0.01 N HCI. After the HCI treatment, seeds were rinsed repeatedly with sterile H20 and germinated on sterile moist filter paper for 2 days. R. japonicum binding to G. soja roots was examined by using the slide-culture method of Fahraeus (13

Adsorption of Slow- and Fast-Growing Rhizobia to Soybean and Cowpea Roots

“…The inocula contained I04 rhizobia/ml, and the data are from 3 experiments. (7) and Chen and Phillips (8) and stand in sharp contrast to earlier reports of strong correlations between the adsorption of rhizobia to host roots and the ability ofthe rhizobia to infect and nodulate (10,11,15,16,22,23). These correlations are most extensive with the fast-growing rhizobia, a group of organisms that differs substantially from the slow-growing strains that infect soybean and cowpea (26).…”

“…and Zucc. ), but cells of nonnodulating Rhizobium strains are reported not to bind to similar roots (22). Certain nonnodulating R. japonicum mutants also apparently fail to bind to soybean roots (23).…”

Correlation between competitive nodulation ability and cell surface hydrophobicity of Bradyrhizobium japonicum.

“…Many observations have revealed polar attachment of rhizobial cells to plant root surface immediately after inoculation (Napoli et al, 1975;Stacey et al, 1980). Marshall et al (1985) demonstrated the hydrophobicity of rhizobial cell surface to be a cause of the polar orientation of the cells at interface.…”

Host Recognition in the Rhizobium-Soybean Symbiosis

“…Stacey et al (18) demonstrated the presence of a Rhizobium binding lectin on the roots of soybean. Gade et al (12) were able to purify soybean lectin from roots and showed that it had similar properties to the seed lectin.…”