title: Molecular characterization of root-specific chalcone synthases from Cassia alata.
abstract: Three cDNAs encoding very similar but unique isoforms of chalcone synthase (EC 2.3.1.74) were isolated from a cDNA library prepared from RNA from root tissue of the Thai medicinal plant Cassia alata L. (ringworm bush, Leguminosae). Gene transcript for these three type-III polyketide synthases was found to accumulate predominantly in roots. The heterologously expressed enzymes accepted acetyl-, n-butyryl-, isovaleryl-, n-hexanoyl-, benzoyl-, cinnamoyl-, and p-coumaroyl-CoA as starter molecules and together with the co-substrate malonyl-CoA, formed multiple products. With the exception of the assay in which acetyl-CoA was used as the starter molecule, all substrates yielded a phloroglucinol derivative resulting from three sequential condensations of acetate units derived from three malonyl-CoA decarboxylations. Every substrate tested also produced two pyrone derivatives, one resulting from two acetate unit condensations (a bis-noryangonin-type pyrone derailment product) and one resulting from three acetate unit condensations (a 4-coumaroyltriacetic acid lactone-type pyrone derailment). C. alata accumulates the flavonoids quercetin, naringenin and kaempferol in roots, suggesting that the in planta function of these enzymes is the biosynthesis of root flavonoids.
authors.affiliation: Leibniz-Institut für Pflanzenbiochemie, Halle/Saale, Germany.
authors.forename: Supachai
authors.initials: S
authors.lastname: Samappito
authors.forename: Jonathan
authors.initials: J
authors.lastname: Page
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schmidt
authors.forename: Wanchai
authors.initials: W
authors.lastname: De-Eknamkul
authors.forename: Toni M
authors.initials: TM
authors.lastname: Kutchan
mesh_terms: D000217:Acyltransferases / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D002366:Cassia / Q000201:enzymology / Q000235:genetics*; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D044950:Flavanones; D005419:Flavonoids / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D044949:Kaempferols; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology* / Q000235:genetics; D010946:Plants, Medicinal; D011794:Quercetin / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D018076:DNA, Complementary; D044950:Flavanones; D005419:Flavonoids; D007527:Isoenzymes; D044949:Kaempferols; D009097:Multienzyme Complexes; C006552:kaempferol; D011794:Quercetin; D000217:Acyltransferases; C020141:flavanone synthetase; C005273:naringenin