Reduction of sinapate ester content in transgenic oilseed rape (Brassica napus) by dsRNAi-based suppression of BnSGT1 gene expression

Seeds of oilseed rape (Brassica napus) accumulate high amounts of antinutritive sinapate esters (SE) with sinapoylcholine (sinapine) as major component, accompanied by sinapoylglucose. These phenolic compounds compromise the use of the protein-rich valuable seed meal. Hence, a substantial reduction of the SE content is considered essential for establishing rape as a protein crop. The present work focuses on the suppression of sinapine synthesis in rape. Therefore, rape (spring cultivar Drakkar) was transformed with a dsRNAi construct designed to silence seed-specifically the BnSGT1 gene encoding UDP-glucose:sinapate glucosyltransferase (SGT1). This resulted in a substantial decrease of SE content in T2 seeds with a reduction reaching 61%. In T2 seeds a high and significant correlation between the contents of sinapoylglucose and all other sinapate esters has been observed. Among transgenic plants, no significant difference in other important agronomic traits, such as oil, protein, fatty acid and glucosinolate content in comparison to the control plants was observed. Maximal reduction of total SE content by 76% was observed in seeds of one homozygous T2 plant (T3 seeds) carrying the BnSGT1 suppression cassette as a single copy insert. In conclusion, this study is an initial proof of principle that suppression of sinapoylglucose formation leads to a strong reduction of SE in rape seeds and is thus a promising approach in establishing rape, currently an important oil crop, as a protein crop as well.