The hepta-beta-glucoside elicitor-binding proteins from legumes represent a putative receptor family.
The ability of legumes to recognize and respond to beta-glucan elicitors by synthesizing phytoalexins is consistent with the existence of a membrane-bound beta-glucan-binding site. Related proteins of approximately 75 kDa and the corresponding mRNAs were detected in various species of legumes which respond to beta-glucans. The cDNAs for the beta-glucan-binding proteins of bean and soybean were cloned. The deduced 75-kDa proteins are predominantly hydrophilic and constitute a unique class of glucan-binding proteins with no currently recognizable functional domains. Heterologous expression of the soybean beta-glucan-binding protein in tomato cells resulted in the generation of a high-affinity binding site for the elicitor-active hepta-beta-glucoside conjugate (Kd = 4.5 nM). Ligand competition experiments with the recombinant binding sites demonstrated similar ligand specificities when compared with soybean. In both soybean and transgenic tomato, membrane-bound, active forms of the glucan-binding proteins coexist with immunologically detectable, soluble but inactive forms of the proteins. Reconstitution of a soluble protein fraction into lipid vesicles regained beta-glucoside-binding activity but with lower affinity (Kd = 130 nM). We conclude that the beta-glucan elicitor receptors of legumes are composed of the 75 kDa glucan-binding proteins as the critical components for ligand-recognition, and of an as yet unknown membrane anchor constituting the plasma membrane-associated receptor complex.
Mithöfer
A
A
Botanisches Institut der Universität, München, Germany.
Fliegmann
J
J
Neuhaus-Url
G
G
Schwarz
H
H
Ebel
J
J
D001483:Base Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D015152:Blotting, Northern; D015139:Blotting, Southern; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D018076:DNA, Complementary / Q000737:chemistry / Q000302:isolation & purification; D007887:Fabaceae / Q000737:chemistry*; D005936:Glucans; D037102:Lectins; D008024:Ligands; D018551:Solanum lycopersicum / Q000737:chemistry / Q000235:genetics; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000737:chemistry / Q000235:genetics; D010946:Plants, Medicinal; D011955:Receptors, Drug / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D030262:Soybean Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D002352:Carrier Proteins; D018076:DNA, Complementary; D005936:Glucans; D037102:Lectins; D008024:Ligands; D008565:Membrane Proteins; D010940:Plant Proteins; D011955:Receptors, Drug; D030262:Soybean Proteins; C037937:glucan-binding proteins; C073685:heptaglucoside