GENETIC-ENGINEERING OF A QUANTITATIVE TRAIT - METABOLIC AND GENETIC-PARAMETERS INFLUENCING THE ACCUMULATION OF LAURATE IN RAPESEED

Laurate can be produced in the seed reserve oil of Brassica napus (rap eseed) by the expression of an heterologous lauroyl acyl-carrier prote in thioesterase under the control of a napin seed-storage protein prom oter. Analysis of a large number of transgenic events, and their proge ny after self-pollination, shows that laurate can accumulate to nearly 60% of the triglyceride acyl groups. Up to 40 mol% laurate the phenot ype is correlated positively with the number of thioesterase gene copi es. The use of a tandem gene construct elevates the average laurate co ntent. This effect correlates with an increased average number of T-DN A insertions per event; no cis-inactivation of tandem genes is apparen t. Above 40 mol% laurate other factors apparently limit the phenotype. The expression timing conferred by the napin promoter is unlikely to be limiting, as it covers almost the entire period of oil deposition. A more significant limitation resides in the second acylation reaction of oil biosynthesis, as shown by the very low incorporation of laurat e at the sn-2 acyl group. The novel, high-laurate oil is consequently rich in sn-1,3-dilauroyl triglycerides, but its unusual composition ap pears to pose no problems for mobilization during seed germination.