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Published on November 5, 2008; 10.1104/pp.108.128066

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Received August 13, 2008
Accepted October 30, 2008

Biosynthesis of t-Anethole in Anise (Pimpinella anisum): Characterization of t-Anol/Isoeugenol Synthase and a O-Methyltransferase Specific for a C7-C8 Propenyl Side Chain

Takao Koeduka , Thomas J. Baiga , Joseph P. Noel , and Eran Pichersky *

Department of Molecular, Cellular and Developmental Biology, University of Michigan, 830 North University Street, Ann Arbor, MI 48109-1048; Howard Hughes Medical Institute, Jack H. Skirball Chemical Biology and Proteomics Laboratory, The Salk Institute for Biological Studies, 10010 N. Torrey Pines Road, La Jolla, CA 92037

* Corresponding author; email: lelx{at}umich.edu.

The phenylpropene t-anethole imparts the characteristic sweet aroma of anise (Pimpinella anisum, family Apiaceae) seeds and leaves. Here we report that the aerial parts of the anise plant accumulate t-anethole as the plant matures, with the highest levels of t-anethole found in fruits. Although the anise plant is covered with trichomes, t-anethole accumulates inside the leaves and not in the trichomes or the epidermal cell layer. We have obtained anise a cDNA encoding t-anol/isoeugenol synthase 1 (AIS1), an NADPH-dependent enzyme that can biosynthesize t-anol and isoeugenol (the latter not found in anise) from coumaryl acetate and coniferyl acetate, respectively. In addition, we have obtained a cDNA encoding SAM:t-anol/isoeugenol O-methyltransferase 1 (AIMT1), an enzyme that can convert t-anol or isoeugenol to t-anethole or methylisoeugenol, respectively, via methylation of the para-OH group. The genes encoding AIS1 and AIMT1 were expressed throughout the plant and their transcript levels were highest in developing fruits. The AIS1 protein is 59% identical to petunia isoeugenol synthase 1 and displays apparent Km values of 145 µM for coumaryl acetate and 230 µM for coniferyl acetate. AIMT1 prefers isoeugenol to t-anol by a factor of 2, with Km values of 19.3 µM for isoeugenol and 54.5 µM for SAM. The AIMT1 protein sequence is approximately 40% identical to basil and Clarkia breweri phenylpropene OMTs, but unlike these enzymes, which do not show large discrimination between substrates with isomeric propenyl side chains, AIMT1 shows a 10-fold preference for t-anol over chavicol and for isoeugenol over eugenol.






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