Untersuchungen zur Sinapinsäureestersuppression und zur Expression von Resveratrol in transgener Rapssaat (Brassica napus L.)

Abstract

In the Brassicaceae family, sinapic acid esters (SAE) are important anti-nutritional compounds. They contribute to the bitter taste and adstringency of rapeseed products. A substantial reduction of sinapic acid esters in oilseed rape could improve its use as a protein crop. Seeds accumulate primarily sinapoyl choline (sinapine) and smaller amounts of sinapoylglucose as well as some other not yet characterized sinapic acid containing compounds. This work focuses on the Agrobacterium tumefaciens mediated transformation of Brassica napus spring cultivar Drakkar with a ds-RNA-interference construct deduced from the sequence of the key enzyme sinapic acid glucosyltransferase (SGT). This resulted in a substantial decrease of sinapic acid esters from 7.28 mg/g in the lowest out of 30 control plants to 2.84 mg/g in the T2-seeds of one T1-plant. Among the transgenic T1-plants was a high and significant correlation between sinapoylglucose and all other sinapic acid esters, which ranged from 0.76** to 0.96**. There was no significant difference in other important agronomic traits, like oil, protein, fatty acid and glucosinolate content in comparison to the control plants. In one homozygous T2-plant with a single copy integrated the total SAE content was reduced to 1.82 mg/g, in comparison to 7.48 mg/g in the lowest out of 22 control plants. The sinapine content in this T2-plant was 2.66 mg/g.Resveratrol, an interesting molecule for transformation, is a phytoalexin produced in several plants like grapevine, peanut and pine in response to fungal infection or UV irradiation. Moreover, resveratrol and its glucoside are considered to have beneficial effects on human health. These compounds are known to reduce heart disease, arteriosclerosis and cancer mortality. Therefore, the introduction of the gene encoding stilbene synthase for resveratrol production in rapeseed is a tempting approach to improve the quality of rapeseed products. The stilbene synthase gene isolated from grapevine (Vitis vinifera L.) under control of the seed specific napin promotor was introduced into rapeseed (Brassica napus L.) by Agrobacterium mediated co-trans-formation together with a ds-RNA-interference construct deduced from the sequence of the key enzyme sinapic acid glucosyltransferase, assuming that the suppression of the sinapic acid ester biosynthesis may increase the resveratrol production in seeds through the increa-sed availability of the precursor p-cumaric acid. Resveratrol glucoside was produced at levels up to 361 µg/g in the seeds of the primary transformants. There was no significant difference in other important agronomic traits, like oil, protein, fatty acid and glucosinolate content in comparison to the control plants. In the next seed generation, up to 424 µg/g resveratrol glucoside was found in seeds of a homozygous T2-plant with a single transgene copy integrated. The sinapic acid ester content in this homozygous T2-plant was reduced from 7.48 mg/g in the lowest out of 22 control plants to 1.30 mg/g.