Elucidation of the final reactions of DIMBOA-glucoside biosynthesis in maize: characterization of Bx6 and Bx7.
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.
Jonczyk
Rafal
R
Technische Universität München, Lehrstuhl für Genetik, Freising, Germany.
Schmidt
Holger
H
Osterrieder
Anne
A
Fiesselmann
Andreas
A
Schullehner
Katrin
K
Haslbeck
Martin
M
Sicker
Dieter
D
Hofmann
Diana
D
Yalpani
Nasser
N
Simmons
Carl
C
Frey
Monika
M
Gierl
Alfons
A
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
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