Abstract

The β-ketoacyl CoA synthase encoded by fatty acid elongase 1 gene (BnFAE1.1) is a rate-limiting enzyme regulating biosynthesis of erucic acid in rapeseeds (Brassica napus). To develop low level of erucic acid in rapeseeds by intron-spliced hairpin RNA, an inverted repeat unit of a partial BnFAE1.1 gene interrupted by a spliceable intron was cloned into pCAMBIA3301, and a seed-specific (Napin) promoter was used to control the transcription of the transgene. Four transgenic plants harboring a single copy of transgene were generated. Expression of endogenous BnFAE1.1gene in developing T₃ seeds was significantly reduced. In mature T₃ seeds, erucic acid was decreased by 60.8 to 99.1% compared with wild type seeds, and accounted for 0.36 to 15.56% of total fatty acids. The level of eicosenoic acid was also greatly decreased. Furthermore, it resulted in a significant increase in the level of oleic acid, but total fatty acid content in T₃ seeds was the same with that in wild type seeds. In conclusion, the expression of endogenous BnFAE1.1 was efficiently silenced by the designed RNAi silencer, causing a significant down-regulation in the level of erucic acid. Therefore, the RNAi-mediated post-transcriptional silencing ofFAE1 gene to reduce oleic acid in rapeseeds was an efficient method to breed some new B. napus lines.

Key words: Brassica napus L., fatty acid elongase, intron-spliced hairpin RNA, down-regulation, erucic acid.

Abbreviation

DAP, Days after pollination; FAE1, fatty acid elongase 1; ihpRNA, intron-spliced hairpin RNA; LEA, low erucic acid; PPT, phosphinothricin; TFAs, total fatty acids; UFA, unsaturated fatty acid; VLCFA, very long chain fatty acid; WT, wild type.