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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Identification of the Wax Ester Synthase/Acyl-Coenzyme A:Diacylglycerol Acyltransferase WSD1 Required for Stem Wax Ester Biosynthesis in Arabidopsis^1,2,[W],[OA]

Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 (F.L., X.W., P.L., D.B., H.Z., L.S., R.J., L.K.); and Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1 (R.J.)

Wax esters are neutral lipids composed of aliphatic alcohols and acids, with both moieties usually long-chain (C₁₆ and C₁₈) or very-long-chain (C₂₀ and longer) carbon structures. They have diverse biological functions in bacteria, insects, mammals, and terrestrial plants and are also important substrates for a variety of industrial applications. In plants, wax esters are mostly found in the cuticles coating the primary shoot surfaces, but they also accumulate to high concentrations in the seed oils of a few plant species, including jojoba (Simmondsia chinensis), a desert shrub that is the major commercial source of these compounds. Here, we report the identification and characterization of WSD1, a member of the bifunctional wax ester synthase/diacylglycerol acyltransferase gene family, which plays a key role in wax ester synthesis in Arabidopsis (Arabidopsis thaliana) stems, as first evidenced by severely reduced wax ester levels of in the stem wax of wsd1 mutants. In vitro assays using protein extracts from Escherichia coli expressing WSD1 showed that this enzyme has a high level of wax synthase activity and approximately 10-fold lower level of diacylglycerol acyltransferase activity. Expression of the WSD1 gene in Saccharomyces cerevisiae resulted in the accumulation of wax esters, but not triacylglycerol, indicating that WSD1 predominantly functions as a wax synthase. Analyses of WSD1 expression revealed that this gene is transcribed in flowers, top parts of stems, and leaves. Fully functional yellow fluorescent protein-tagged WSD1 protein was localized to the endoplasmic reticulum, demonstrating that biosynthesis of wax esters, the final products of the alcohol-forming pathway, occurs in this subcellular compartment.

² This work is part of ICON, a European Community Seventh Framework Programme.

³ Present address: Department of Biological Sciences, University of Manitoba, Winnipeg Manitoba, Canada R3T 2N2.

⁴ Present address: Department of Biology, McGill University, Montreal, Quebec, Canada H3A 1B1.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Ljerka Kunst (kunst{at}interchange.ubc.ca).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.123471

^* Corresponding author; e-mail kunst{at}interchange.ubc.ca.

Received May 23, 2008; accepted July 9, 2008; published July 11, 2008.

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