title: Identification and functional characterization of genes encoding omega-3 polyunsaturated fatty acid biosynthetic activities from unicellular microalgae.
abstract: In order to identify novel genes encoding enzymes involved in the biosynthesis of nutritionally important omega-3 long chain polyunsaturated fatty acids, a database search was carried out in the genomes of the unicellular photoautotrophic green alga Ostreococcus RCC809 and cold-water diatom Fragilariopsis cylindrus. The search led to the identification of two putative "front-end" desaturases (Δ6 and Δ4) from Ostreococcus RCC809 and one Δ6-elongase from F. cylindrus. Heterologous expression of putative open reading frames (ORFs) in yeast revealed that the encoded enzyme activities efficiently convert their respective substrates: 54.1% conversion of α-linolenic acid for Δ6-desaturase, 15.1% conversion of 22:5n-3 for Δ4-desaturase and 38.1% conversion of γ-linolenic acid for Δ6-elongase. The Δ6-desaturase from Ostreococcus RCC809 displays a very strong substrate preference resulting in the predominant synthesis of stearidonic acid (C18:4Δ6,9,12,15). These data confirm the functional characterization of omega-3 long chain polyunsaturated fatty acid biosynthetic genes from these two species which have until now not been investigated for such activities. The identification of these new genes will also serve to expand the repertoire of activities available for metabolically engineering the omega-3 trait in heterologous hosts as well as providing better insights into the synthesis of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in marine microalgae.
authors.forename: Royah
authors.initials: R
authors.lastname: Vaezi
authors.forename: Johnathan A
authors.initials: JA
authors.lastname: Napier
authors.affiliation: Department of Biological Chemistry and Crop Protection, Rothamsted Research, Harpenden, Herts AL5 2JQ, UK. olga.sayanova@rothamsted.ac.uk.
authors.forename: Olga
authors.initials: O
authors.lastname: Sayanova
mesh_terms: D000460:Chlorophyta / Q000235:genetics / Q000378:metabolism; D017377:Diatoms / Q000235:genetics / Q000378:metabolism; D004281:Docosahexaenoic Acids / Q000235:genetics / Q000378:metabolism; D015118:Eicosapentaenoic Acid / Q000235:genetics / Q000378:metabolism; D044943:Fatty Acid Desaturases / Q000235:genetics / Q000378:metabolism; D015525:Fatty Acids, Omega-3 / Q000235:genetics* / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000235:genetics* / Q000378:metabolism*; D058086:Microalgae / Q000235:genetics* / Q000378:metabolism*; D015003:Yeasts / Q000235:genetics / Q000378:metabolism; D017962:alpha-Linolenic Acid / Q000235:genetics / Q000378:metabolism
chemical_list: D015525:Fatty Acids, Omega-3; D005231:Fatty Acids, Unsaturated; D017962:alpha-Linolenic Acid; D004281:Docosahexaenoic Acids; D015118:Eicosapentaenoic Acid; D044943:Fatty Acid Desaturases; C062895:stearidonic acid