The invention relates to a method for producing unsaturated fatty acidscomprising at least two double bonds, and a method for producing triglycerideshaving an increased content of polyunsaturated fatty acids comprising at leasttwo double bonds. The invention also relates to the advantageous use of thenucleic acid sequences of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO:9, SEQ ID NO: 11 or SEQ ID NO: 18 in the inventive methods, and for producinga transgenic organism, preferably a transgenic plant or a transgenic micro-organism having an increased content of fatty acids, oils or lipids containingunsaturated C18, C20, or C22 fatty acids. The invention further relates tonovel desaturases comprising the sequences of SEQ ID NO. 1, SEQ ID NO: 3, SEQID NO: 5 and SEQ ID NO: 11, or the homologues, derivatives or analoguesthereof, and gene constructs comprising said genes or the homologues,derivatives or analogues thereof, in addition to the use of the same, eitheralone or combined with biosynthesis genes of polyunsaturated fatty acids, asadvantageously represented in SEQ ID NO: 7 and SEQ ID NO: 9. Furthermore, theinvention relates to isolated nucleic acid sequences, expression cassettescontaining said nucleic acid sequences, vectors, and transgenic organismscontaining at least one nucleic acid sequence or an expression cassette. Theinvention also relates to unsaturated fatty acids comprising at least twodouble bonds and triglycerides having an increased content of unsaturatedfatty acids comprising at least two double bonds, and the use of the same.Finally, the invention relates to multi-expression cassettes for seed-specificexpression, in addition to vectors or organisms comprising a desaturase gene,either alone or combined with other desaturases having the sequence of SEQ IDNO: 7 and/or elongase genes having the sequence of ID NO: 9 or the homologues,derivatives or analogues of the same, expressed by means of the above-mentioned expression cassettes.
