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Papers In Press, published online ahead of print October 1, 2004
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* Biozentrum Klein Flottbek, Universität Hamburg, D-22609 Hamburg, Germany
BASF Plant Science GmbH, D-67056 Ludwigshafen, Germany
Laboratoire Arago, Unité Mixte de Recherche 7628, Centre National de la Recherche Scientifique, F-66651 Banyuls sur mer, France
** Laboratoire de Génome et Développement des Plantes, Unité Mixte de Recherche 5096, Centre National de la Recherche Scientifique, F-66860 Perpignan, France

Forschungszentrum Borstel, D-23845 Borstel, Germany
1 To whom correspondence should be addressed. e-mail: eheinz{at}botanik.uni-hamburg.de
In algae, the biosynthesis of docosahexaenoic acid (22:6
3; DHA) proceeds via the elongation of eicosapentaenoic acid (20:5
3; EPA) to 22:5
3, which is required as a substrate for the final
4 desaturation. To isolate the elongase specific for this step, we searched expressed sequence tag and genomic databases from the algae Ostreococcus tauri and Thalassiosira pseudonana, from the fish Oncorhynchus mykiss, from the frog Xenopus laevis, and from the sea squirt Ciona intestinalis using as a query the elongase sequence PpPSE1 from the moss Physcomitrella patens. The open reading frames of the identified elongase candidates were expressed in yeast for functional characterization. By this, we identified two types of elongases from O. tauri and T. pseudonana: one specific for the elongation of (
6-)C18-PUFAs and one specific for (
5-)C20-PUFAs, showing highest activity with EPA. The clones isolated from O. mykiss, X. laevis, and C. intestinalis accepted both C18- and C20-PUFAs. By coexpression of the
6- and
5-elongases from T. pseudonana and O. tauri, respectively, with the
5- and
4-desaturases from two other algae we successfully implemented DHA synthesis in stearidonic acid-fed yeast.
This may be considered an encouraging first step in future efforts to implement this biosynthetic sequence into transgenic oilseed crops.
Abbreviations: ALA,
-linolenic acid; ARA, arachidonic acid; DHA, docosahexaenoic acid; EPA, eicosapentaenoic acid; EST, expressed sequence tag; GLA,
-linolenic acid; LA, linoleic acid; LCPUFA, long-chain polyunsaturated fatty acid; ORF, open reading frame; STA, stearidonic acid
Supplementary key words Ciona intestinalis Oncorhynchus mykiss Ostreococcus tauri polyunsaturated fatty acids Thalassiosira pseudonana Xenopus laevis
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