title: Elucidation of the final reactions of DIMBOA-glucoside biosynthesis in maize: characterization of Bx6 and Bx7.
abstract: Benzoxazinoids were identified in the early 1960s as secondary metabolites of the grasses that function as natural pesticides and exhibit allelopathic properties. Benzoxazinoids are synthesized in seedlings and stored as glucosides (glcs); the main aglucone moieties are 2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one (DIBOA) and 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA). The genes of DIBOA-glc biosynthesis have previously been isolated and the enzymatic functions characterized. Here, the enzymes for conversion of DIBOA-glc to DIMBOA-glc are identified. DIBOA-glc is the substrate of the dioxygenase BENZOXAZINLESS6 (BX6) and the produced 2,4,7-trihydroxy-2H-1,4-benzoxazin-3-(4H)-one-glc is metabolized by the methyltransferase BX7 to yield DIMBOA-glc. Both enzymes exhibit moderate K(m) values (below 0.4 mm) and k(cat) values of 2.10 s(-1) and 0.25 s(-1), respectively. Although BX6 uses a glucosylated substrate, our localization studies indicate a cytoplasmic localization of the dioxygenase. Bx6 and Bx7 are highest expressed in seedling tissue, a feature shared with the other Bx genes. At present, Bx6 and Bx7 have no close relatives among the members of their respective gene families. Bx6 and Bx7 map to the cluster of Bx genes on the short arm of chromosome 4.
authors.affiliation: Technische Universität München, Lehrstuhl für Genetik, Freising, Germany.
authors.forename: Rafal
authors.initials: R
authors.lastname: Jonczyk
authors.forename: Holger
authors.initials: H
authors.lastname: Schmidt
authors.forename: Anne
authors.initials: A
authors.lastname: Osterrieder
authors.forename: Andreas
authors.initials: A
authors.lastname: Fiesselmann
authors.forename: Katrin
authors.initials: K
authors.lastname: Schullehner
authors.forename: Martin
authors.initials: M
authors.lastname: Haslbeck
authors.forename: Dieter
authors.initials: D
authors.lastname: Sicker
authors.forename: Diana
authors.initials: D
authors.lastname: Hofmann
authors.forename: Nasser
authors.initials: N
authors.lastname: Yalpani
authors.forename: Carl
authors.initials: C
authors.lastname: Simmons
authors.forename: Monika
authors.initials: M
authors.lastname: Frey
authors.forename: Alfons
authors.initials: A
authors.lastname: Gierl
mesh_terms: D048588:Benzoxazines / Q000378:metabolism*; D032461:Chromosomes, Plant; D003593:Cytoplasm / Q000201:enzymology; D017343:Genes, Plant; D005960:Glucosides / Q000096:biosynthesis* / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D011497:Protein O-Methyltransferase / Q000235:genetics / Q000378:metabolism*; D036226:Seedlings / Q000201:enzymology; D003313:Zea mays / Q000201:enzymology* / Q000235:genetics
chemical_list: C418135:2-O-glucopyranosyl-4-hydroxy-7-methoxy-1,4-benzoxazin-3-one; D048588:Benzoxazines; D005960:Glucosides; C104846:2,4-dihydroxy-1,4-benzoxazin-3-one; D011497:Protein O-Methyltransferase; C050733:2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one