Enzymes and methods for producing omega-3 fatty acids
The present invention relates generally to the field of recombinant fatty acid synthesis, particularly in transgenic plants. The application describes genes involved in fatty acid synthesis and provides methods and vectors for the manipulation of fatty acid composition of plant oils. In particular, the invention provides constructs for achieving the integration of multiple heterologous genes involved in fatty acid synthesis into the plant genome, such that the resulting plants produce altered levels of polyunsaturated fatty acids. Also described are methods for enhancing the expression of fatty acid biosynthesis enzymes by co-expressing a silencing suppressor within the plant storage organ.
1. A Brassica napus cell, comprising exogenous polynucleotides encoding
a Δ6 desaturase whose amino acid sequence is set forth as SEQ ID NO:30,
a Δ6 elongase,
a Δ5 desaturase whose amino acid sequence is identical to the amino acid sequence encoded by the nucleotide sequence set forth as SEQ ID NO: 131,
a Δ5 elongase whose amino acid sequence is at least 99% identical to the amino acid sequence set forth as SEQ ID NO: 130, and
a Δ4 desaturase whose amino acid sequence is identical to the amino acid sequence encoded by the nucleotide sequence set forth as SEQ ID NO: 132,
wherein each exogenous polynucleotide is operably linked to a promoter that directs expression of said polynucleotide in the cell.
2. The Brassica napus cell of claim 1 , wherein the Δ6 elongase has the amino acid sequence which is identical to the amino acid sequence encoded by the nucleotide sequence set forth as SEQ ID NO: 133.
3. The Brassica napus cell of claim 1 which is a Brassica napus seed cell.
4. A Brassica napus seed comprising the Brassica napus seed cell of claim 3 .
5. The Brassica napus seed of claim 4 , comprising a total fatty acid content which comprises α-linolenic acid (ALA), stearidonic acid (SDA), eicosatetraenoic acid (ETA), eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA), wherein the ALA, SDA, ETA, EPA, DPA and DHA are each present at a level in the total fatty acid content, each level being expressed as a percentage of the total fatty acid content, such that the sum of the percentages for DPA and DHA divided by the sum of the percentages for ALA, SDA, ETA, EPA, DPA and DHA, expressed as a percentage, is at least 15.4%.
6. The Brassica napus seed of claim 4 , wherein arachidonic acid (ARA), EPA, DPA and DHA together comprise 15% of the total fatty acid content.
7. A process for producing oil, comprising a step of extracting oil from the Brassica napus seed of claim 4 .
8. The process of claim 7 , comprising a step of purifying the extracted oil.
9. A process for producing oil, comprising a step of extracting oil from the Brassica napus seed of claim 5 .
10. The process of claim 9 , wherein the seed comprises DPA and DHA in an esterified form as part of triacylglycerols.
11. The process of claim 10 , comprising a step of purifying the extracted triacylglycerols.
12. A process for producing oil, comprising a step of extracting oil from the Brassica napus seed of claim 6 .