| Rapeseed (Brassica napus L.) is the most important oil crop in China. A great number of new double-low rape varieties have been developed and released by the conventional breeding, and basically popularized to all planted areas. In practical production of double-low rape, however, rapeseed quality was greatly affected by the increase in erucic acid content derived from pollination of pollens from high erucic acid plants around. Transgenic technology can play a unique role in solving the above-mentioned problem. Therefore, development of new rape varieties with low erucic acid content by genetic engineering is still of great significance and good application prospect.Chaoyou 2, the new Brassica napus strain with high oil and low glucosinolate content, high yield and excellent comprehensive characters, has been successfully bred by our laboratory. Because of its high erucic acid content (44%), however, utilization of this strain as a new edible rape cultivar is conditioned. With Chaoyou 2 as starting material in present study, hypocotyls were transformed with the RNAi and antisense expression vectors of fatty acid elongase 1 gene FAE1, which is the key gene in the biosynthesis of erucic acid. Molecular identification, genetic analysis, quality measurement and investigation of agronomic characters of the transformed plants were carried out. The main results were as follows:1. By Agrobacterium tumefaciens-mediated transformation,104 To transformed plants were regenerated and survived from transplantation, including 76 ones for RNAi expression and 28 for antisense expression.2.86 independent transgenic plants (65 for RNAi expression and 21 for antisense expression) were finally confirmed by Basta spraying, PCR detection, Southern blotting, RT-PCR analysis and Genome PCR Walking. Moreover, transfer to T1 generation and expression of the target gene had been demonstrated.3. Genetic analysis of a part of T1 transgenic lines indicated that the target gene in the genome mostly belonged to single-site and double-site insertion, whereas multi-site insertion was found in some lines.4. Quality analysis showed that erucic acid content was significantly decreased in To transformed plants and T1 transgenic lines with RNA interference expression of FAE1 gene compared with the control, with the lowest erucic acid content being about 1%. In addition, it was found that there were great differences in erucic acid content among the different transgenic plants and lines. The above results indicated that the biosynthesis of erucic acid had been effectively inhibited by RNAi expression of FAE1 gene. Quality analysis also showed that oil content was decreased to different extents in a part of To transformed plants and T1 transgenic lines in comparison with the control, whereas in the other plants and lines, oil content was similar to that of the control. Now, excellent single plant with oil content of 51.7% and erucic acid content of 1% had been screened out.5. In a part of T1 transgenic lines with RNA interference expression of FAE1 gene, significant or very significant variations have taken place for grain number per pod and primary branch position, but not for plant height, primary branch number, secondary branch number, pod number per plant,1000-grain weight and yield per plant.In summary:the transgenic plant with oil content of 51.7% and erucic acid content of 1% were obtained in this study. Meanwhile, a new technology for inhibition of erucic acid biosynthesis by genetic engineering was established. The establishment of this technology is of great significance for breeding of new Brassica napus varieties with stable low erucic acid content.
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