Expression of borage Delta 6 desaturase in Saccharomyces cerevisiae and oilseed crops
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abstract
The borage 6 desaturase is a modular protein that contains a cytochrome b5-like domain attached to the N-terminus of the main catalytic domain. When the full-length open reading frame was expressed in two types of Saccharomyces cerevisiae strains, the endogenous cytochrome b5-disrupted strain and the cytochrome b5-competent wild type strain, the expressed enzyme introduced a double bond at the 6 position into the endogenous substrates 16:1(9) and 18:1(9), and also into the exogenously fed fatty acid substrates 18:2(9,12) and 18:3(9,12,15). However, the preferred substrates of the enzyme when expressed in yeast were 18:2(9,12) and 18:3(9,12,15), whereas 16:1(9) and 18:1(9) were relatively poor substrates. When the partial desaturase sequence with a deletion of the cytochrome b5-like domain at the N-terminus was introduced into the yeast strains, the truncated enzyme could not desaturate any of the supplied substrates. Introduction of the full-length cDNA into flax (Linum usitatissimum L.) under the control of a constitutive (35S) promoter resulted in accumulation of the two 6 desaturated fatty acids (18:3(6,9,12) and 18:4(6,9,12,15)), in one elite line, forming up to 22% of the total fatty acids in the stem, 19% in the root, and 11% in the leaf. Introduction of the desaturase into Brassica juncea (L.) Czern. under the control of the Brassica napus L. napin promoter resulted in accumulation of the 6 desaturated fatty acids at levels of up to 13% of the total fatty acids in mature seeds.Key words: borage, 6 desaturase, -linolenic acid, stearidonic acid, Brassica juncea, flax.
