Release of Flavonoids by the Soybean Cultivars McCall and Peking
and Their Perception as Signals by the Nitrogen-Fixing Symbiont
Sinorhizobium fredii |
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| Authors: | Steven G. Pueppke Maria Cristina Bola?os-Vásquez Dietrich Werner Marie-Pierre Bec-Ferté Jean-Claude Promé Hari B. Krishnan |
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| Affiliation: | Department of Plant Pathology, University of Missouri, Columbia, Missouri 65211 (S.G.P., H.B.K.);Fachbereich Biologie der Philipps Universität, Karl-von-Frisch Strasse, D-35032 Marburg, Germany (M.C.B.-V., D.W.);Laboratoire de Pharmacologie et de Toxicologie Fondimentales du Centre National de la Recherche Scientifique, 205 Route de Narbonne, 31077 Toulouse cedex, France (J.-C.P., M.-P.B.-F.) |
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| Abstract: | Sinorhizobium fredii strain USDA191 forms N-fixing nodules on the soybean (Glycine max L. Merr.) cultivars (cvs) McCall and Peking, but S. fredii strain USDA257 nodulates only cv Peking. We wondered whether specificity in this system is conditioned by the release of unique flavonoid signals from one of the cultivars or by differential perception of signals by the strains. We isolated flavonoids and used nodC and nolX, which are nod-box-dependent and -independent nod genes, respectively, to determine how signals activate genes in the microsymbionts. Seeds of cv McCall and cv Peking contain the isoflavones daidzein, genistein, and glycitein, as well as their glucosyl and malonylglucosyl glycosides. Roots exude picomolar concentrations of daidzein, genistein, glycitein, and coumestrol. Amounts are generally higher in cv Peking than in cv McCall, and the presence of rhizobia markedly influences the level of specific signals. Nanomolar concentrations of daidzein, genistein, and coumestrol induce expression of nodC and nolX in strain USDA257, but the relative nolX-inducing activities of these signals differ in strain USDA191. Glycitein and the conjugates are inactive. Strain USDA257 deglycosylates daidzin and genistin into daidzein and genistein, respectively, thereby converting inactive precursors into active inducers. Although neither soybean cultivar contains unique nod-gene-inducing flavonoids, strain- and cultivar-specific interactions are characterized by distinct patterns of signal release and response. |
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