Specific targeting of membrane nodulins to the bacteroid-enclosing compartment in soybean nodules

Abstract

Rhizobium bacteroids in nodule cells are surrounded by the peribacteroid membrane (pbm), which is derived from the host plasma membrane during infection. The pbm was purified from R. japonicum 61A76‐induced soybean nodules and analyzed by comparing it with the host cell plasma membrane for the presence of nodulins, nodule‐specific plant proteins. Nodulins were found in pbm by reacting Western blots with a nodule‐specific antiserum raised against the pbm. Peribacteroid fluid (the fluid enclosed in the pbm) was also found to contain several nodulins. The pbm nodulins were confirmed to be of plant origin by in vitro translation of poly(A)+ nodule mRNA followed by immunoprecipitation by the nodule‐specific antiserum. Antibodies raised against a synthetic peptide corresponding to a repeated domain in nodulin‐24, a pbm nodulin, and the nodule‐specific pbm antiserum reacted exclusively with the pbm. The absence of pbm‐nodulins in the plasma membrane suggests that the infected cells direct the intracellular transport of the pbm nodulins exclusively to this de novo synthesized subcellular compartment essential for symbiotic nitrogen fixation.

The effect of different temperatures on the fatty acid composition of Rhizobium leguminosarum bv. viciae in the faba bean symbiosis

“…Bacteroids lacking their peribacteroid membranes (PBM) were purified as described by Fortin, Selechowska & Verma (1985) and Bassarab et al (1989) with slight modifications. Washed nodules (20 g f. wt) were ground with a mortar and pestle in 50 ml of cold TB buffer (50 mol m"^ Tris-HCl, pH 8-0, 5 mol m''" FDTA, 5 mol mercaptoethanol, 1 mol m~' phenylmethylsulfonyl-fluoride) containing 500 mol m"' sucrose, rapidly filtered through Miracloth® (Chicopee Mills Inc., Milltown, NJ, USA), and centrifuged at 400^ for 10 min at 4 °C.…”

Phosphorylation of Soybean Nodulin 26 on Serine 262 Enhances Water Permeability and Is Regulated Developmentally and by Osmotic Signals

“…During the biogenesis of the symbiosome, a number of plant-encoded nodule-specific gene products (nodulins) are targeted to the symbiosome membrane, where they are presumed to aid in the establishment and maintenance of symbiosis (Fortin et al, 1985;Panter et al, 2000). Nodulin 26 is a symbiosome membrane-specific protein that is the major protein component of this membrane (Fortin et al, 1987;Weaver et al, 1991).…”

Ammonia permeability of the soybean nodulin 26 channel

“…The efflux of fixed nitrogen from the symbiosome space to the infected cell cytosol is mediated by SM transport by one of the two potential mechanisms: 1. Directional transport of NH 4 + cations to the cytosol by an inwardly rectified, voltage-activated non-selective cation channel [24]; or 2. Efflux of uncharged NH 3 through the SM with nod26 providing a low energy pathway for this movement.…”

“…Liposome samples (20 ll) in 250 mM sorbitol, 30 mM KCl, 10 mM HEPES-KOH, pH 6.8 were injected into an equivalent volume of 250 mM sorbitol, 30 mM KCl, 10 mM NH 4 Cl, 10 mM HEPES-KOH, pH 6.8 and the increase in CF fluorescence resulting from NH 3 uptake and alkalinization of the internal liposome space was monitored. Under the conditions of this experiment, changes of in internal pH were linearly correlated with changes of the relative fluorescence.…”

“…Because of the specialized function of the SM, a number of host nodulin proteins are synthesized and localized to this membrane, and serve transport and regulatory functions in the symbiosis [4,5]. Soybean nodulin 26 (nod26) is among this collection of SM nodulins [6].…”