Rhizobia catabolize nod gene-inducing flavonoids via C-ring fission mechanisms.
Gas chromatographic and mass spectrometric analyses of derivatized culture medium extracts were used to identify the products of flavonoid metabolism by rhizobia. A number of Rhizobium species and biovars degraded their nod gene-inducing flavonoids by mechanisms which originated in a cleavage of the C-ring of the molecule and which yielded conserved A- and B-ring products among the metabolites. In contrast, Pseudomonas putida degraded quercetin via an initial fission in its A-ring, and Agrobacterium tumefaciens displayed a nonspecific mode of flavonoid degradation which yielded no conserved A- or B-ring products. When incubated with rhizobia, flavonoids with OH substitutions at the 5 and 7 positions yielded phloroglucinol as the conserved A-ring product, and those with a single OH substitution at the 7 position yielded resorcinol. A wider range of structures was found among the B-ring derivatives, including p-coumaric, p-hydroxybenzoic, protocatechuic, phenylacetic, and caffeic acids. The isoflavonoids genistein and daidzein were also degraded via C-ring fission by Rhizobium fredii and Rhizobium sp. strain NGR234, respectively. Partially characterized aromatic metabolites with potential nod gene-inducing activity were detected among the products of naringenin degradation by Rhizobium leguminosarum bv. viciae. The initial structural modification of nod gene-inducing flavonoids by rhizobia can generate chalcones, whose open C-ring system may have implications for the binding of inducers to the nodD gene product.
Rao
J R
JR
Department of Applied Plant Science, Queen's University of Belfast, Northern Ireland, United Kingdom.
Cooper
J E
JE
D016960:Agrobacterium tumefaciens / Q000254:growth & development / Q000378:metabolism; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000378:metabolism; D002849:Chromatography, Gas; D004269:DNA, Bacterial / Q000378:metabolism*; D005419:Flavonoids / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D005798:Genes, Bacterial; D015394:Molecular Structure; D016958:Pseudomonas putida / Q000254:growth & development / Q000378:metabolism; D012231:Rhizobium / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D016961:Rhizobium leguminosarum / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D013045:Species Specificity; D014157:Transcription Factors
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D005419:Flavonoids; C060773:NodD protein, Bacteria; D014157:Transcription Factors