| Vegetable oil is the major composition of human food consumption, 71% of which is consumed in human daily life and diets. It mainly occurs as triacylglycerol (TAG), whose main function and economic value of vegetable oil are determined by fatty acids. Fatty acids play very important roles not only in food industry, but also in cold tolerance and insect-assistance of plants. They are also major materials in chemical products. Some research on nutrition indicated that content and composition of fat in food was closely related to human health. Polyunsaturated fatty acid (PUFA), involving two or more double bonds in its long carbon chain, is benefit to the treatment of coronary heat disease and the development of intelligence and vision ability. It is known that, common vegetable oil are not qualified for its character in food and nutrition. Therefore, scientists tried to control the synthesis of PUFA by the way of plant genetic engineering.There are many kinds of PUFA in plants, such as γ-linolenic acid (GLA), α-linolenic acid (ALA), arachidonic acid (AA), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), etc. Of them, α-linolenic acid (18:3A9,12,15) is the precursor of DHA and EPA. It is the necessary for human body, and has physiological function in improving intelligence and rememberance, as well as in protecting eyesight, preventing myocardial infarction and hyperlipemia. It originated from ω-3 fatty acid desaturase catalyzing linoleic acid (18:2△9,12), which is an important enzyme that can restrict the speed of fatty acid synthesis. Thus, in order to provide certain beneficial lipids for edible and medical use, we can try to increase the content of necessary fatty acids including α-linolenic acid in a certain plant, by adding the gene copies to enhance the expression level of the gene.Perilla and evening primrose are both special oilseeds in China. They have strongadaptability that can endure leanness and drought, and are suitable to cultivate broadly in West China. Either of them is the research object of oil engineering, which has good applied foreground. Perilla has the richest content of α-linolenic acid in all oilseeds, ranging from 56% to 65% in all the fatty acids, while evening primrose contains both a- and rare γ-linolenic acid.Full-length co-3 fatty acid desaturase cDNA was cloned from perilla (Perilla frutescens (L.) Britt. var. arguta (Benth.)Hand. Mazz.) by PCR using specific primers and was ligated into pGM-T easy vector. Positive clones were selected and the recombinant plasmid was isolated from E.coli DH10B and identified by sequencing. Digested by Xba\ and BamHI. The target gene was constructed into pR0K2 vector digested with the same enzymes. Plant transformation vector pf-pR0K2 was constructed to express co-3 fatty acid desaturase gene under control of the CaMV35S promoter. Tobacco was transformed by co-cultivating leaf dics with Agrobatenum strains AGL1 harboring pf-pROK2. The regenerated Kanamycin-resistant transformants were analyzed by PCR and PCR-Southern. The PCR results indicated that 13 positive transgenic tobacco were gained, and 2 bands about 3kb and 4.5kb were found in the result of Southern blot in most clones, and that another band about 10kb was seen in the result of Southern blot in the clone 28#. The further Southern blot and gas chromatography detecting the increasing of α-linolenic acid in transgenic tobacco is still going on, and expression of the target cDNA in model plants is expected to be approved by Northern blot and RT-PCR later.The same gene, FAD3, was firstly cloned from evening primrose (Oenethera biennis L) and was found to be very conservative with that from perilla. The expression pattern of the gene in 15, 20 and 25 days' seeds after flowering are studied by semi-quantitive RT-PCR and the result indicated the target cDNA was expressed constantly and steadily during the development of seeds from 15 to 25 days after flowering. Expression pattern of the gene in different plant organs are still going on.
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