Effects of genomic position and copy number of acyl-ACP thioesterase transgenes on the level of the target fatty acids in Brassica napus L.

The effects of genomic position and copy number of acyl-acyl carrier protein (ACP) thioesterase (TE) transgenes on the major target fatty acid, either lauric acid ( C12:0) or palmitic acid (C16: 0) depending on the TE, in transgenic Brassica napus seed oil were investigated. Four transgenic parental lines, transformed individually with the bay-TE (Uc FatB1), elm-TE (Ua FatB1), nutmeg-TE (Mf FatB1) and Cuphea-TE (Ch FatB1) transgenes, were crossed with the non-transgenic recipient genotypes '212/86' or 'QO4'. Bay-TE and Cuphea-TE F-1 seeds, which carry half the number of the construct copies compared to the self-pollinated seeds of the transgenic parents, showed significantly lower levels of the target fatty acid. Doubled haploid (DH) lines were developed through microspore culture from F-1 hybrids with the elm-TE or the Cuphea-TE transgenes. DH lines carrying one to five copies of the Cuphea-TE transgene displayed a positive correlation between transgene copy number and the target fatty acid C16: 0 level ( r = 0.77**). DH lines with elm-TE transgene copies at four different loci showed different C16: 0 levels, with one of the loci (E-II) leading to significantly higher C16: 0 levels. This study supports the importance of the selection of high transgene copy number and/or the optimum genomic integration site in order to achieve maximum expression levels of the target fatty acid in transgenic oil quality modification.