Eugenol and isoeugenol, characteristic aromatic constituents of spices, are biosynthesized via reduction of a coniferyl alcohol ester

doi:10.1073/pnas.0603732103

Eugenol and isoeugenol, characteristic aromatic constituents of spices, are biosynthesized via reduction of a coniferyl alcohol ester

*Department of Molecular, Cellular, and Developmental Biology, University of Michigan, 830 North University Street, Ann Arbor, MI 48109-1048;
^§Department of Plant Sciences and Institute for Biomedical Science and Biotechnology, University of Arizona, Tucson, AZ 85721-0036;
^¶Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340;
^‖Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, IN 47907; and
**Howard Hughes Medical Institute, Jack H. Skirball Chemical Biology and Proteomics Laboratory, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037

Communicated by Anthony R. Cashmore, University of Pennsylvania, Philadelphia, PA, May 5, 2006
↵ ^†T.K., E.F., and D.R.G. contributed equally to this work. (received for review March 31, 2006)

Abstract

Phenylpropenes such as chavicol, t-anol, eugenol, and isoeugenol are produced by plants as defense compounds against animals and microorganisms and as floral attractants of pollinators. Moreover, humans have used phenylpropenes since antiquity for food preservation and flavoring and as medicinal agents. Previous research suggested that the phenylpropenes are synthesized in plants from substituted phenylpropenols, although the identity of the enzymes and the nature of the reaction mechanism involved in this transformation have remained obscure. We show here that glandular trichomes of sweet basil (Ocimum basilicum), which synthesize and accumulate phenylpropenes, possess an enzyme that can use coniferyl acetate and NADPH to form eugenol. Petunia (Petunia hybrida cv. Mitchell) flowers, which emit large amounts of isoeugenol, possess an enzyme homologous to the basil eugenol-forming enzyme that also uses coniferyl acetate and NADPH as substrates but catalyzes the formation of isoeugenol. The basil and petunia phenylpropene-forming enzymes belong to a structural family of NADPH-dependent reductases that also includes pinoresinol–lariciresinol reductase, isoflavone reductase, and phenylcoumaran benzylic ether reductase.

Footnotes

^††To whom correspondence should be addressed. E-mail: lelx{at}umich.edu
↵ ^‡Present address: Smith Institute for Plant Sciences and Genetics, Faculty of Agriculture, Hebrew University, P.O. Box 12, Rehovot 76100, Israel.
Author contributions: T.K., E.F., D.R.G., J.P.N., N.D., and E.P. designed research; T.K., E.F., D.R.G., D.G.V., B.L.J., C.M.K., I.O., and S.M.S. performed research; D.G.V., S.M.S., N.G.L., and T.J.B. contributed new reagents/analytic tools; T.K., E.F., D.R.G., D.G.V., B.L.J., C.M.K., I.O., N.G.L., J.P.N., T.J.B., N.D., and E.P. analyzed data; and T.K., E.F., D.R.G., N.G.L., J.P.N., T.J.B., N.D., and E.P. wrote the paper.
Conflict of interest statement: No conflicts declared.
Abbreviations:

Abbreviations:

PLR,

pinoresinol–lariciresinol reductase;

IFR,

isoflavone reductase;

PCBER,

phenylcoumaran benzylic ether reductase.