Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Published on January 11, 2008; 10.1104/pp.107.111237

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Received October 18, 2007
Accepted January 8, 2008

Elucidation of the final reactions of DIMBOA-glucoside biosynthesis in maize: Characterization of Bx6 and Bx7

Rafal Jonczyk , Holger Schmidt , Anne Osterrieder , Andreas Fießelmann , Katrin Schullehner , Martin Haslbeck , Dieter Sicker , Diana Hofmann , Nasser Yalpani , Carl Simmons , Monika Frey *, and Alfons Gierl

Technische Universitat Munchen, Lehrstuhl fur Genetik, Am Hochanger 8, 85354 Freising; Technische Universitat Munchen, Department Chemie, Lehrstuhl Biotechnologie, Lichtenbergstrasse 4, 85747 Garching; Institut for Organic Chemistry, Universitat Leipzig, Johannisallee 29 04103 Leipzig; Institut fur Analytische Chemie, Universitat Leipzig, Johannisallee 29, 04103 Leipzig; Pioneer Hi-Bred International, Inc., 7300 Northwest 62nd Avenue, P.O. Box 1004, Johnston, Iowa 50131

* Corresponding author; email: Monika.Frey{at}wzw.tum.de.

Benzoxazinoids have been 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, the main aglucone moieties are DIBOA (2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one) and DIMBOA (2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one). The genes of DIBOA-glucoside 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 BX6, the produced TRIBOA-glc is metabolized by the methyltransferase BX7 to yield DIMBOA-glc. Both enzymes exhibit moderate Km-values (below 0.4 mM) and kcat values of 2.10 s-1 and 0.25 s-1, respectively. Although BX6 uses a glucosylated substrate, our localization studies indicate a cytoplasmatic 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.




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