Identification And Genetic Stability Analysis Of Transgenic Soybean With An Enhanced Level Of Methionine

Methionine, a sulfur-containing amino acid, is one of the essential amino acids can not be synthesized in humans and animals. It plays an important role in human and animal nutrition because of its involvement in mutiple important biological processes. As an important food crop, soybean [Glycine max(L.) Merr.] is an important staple source of edible oil and vegetal protein in human food. However, the low concentration of the sulfur amino acids in soybean limits its nutritinoal and utilization value. Therefore, increasing the Met content have great significance in the nutritional quality improvement. In our previous study, a CGS gene cloned from Arabidopsis [Arabidopsis thaliana(L.) Heynh] had been transformed into the soybean cultivar Zigongdongdou by the method of Agrobacterium-mediated Transformation in Soybean. The total Met content significantly increased in transgenic plants.The stability of exogenous gene in transgenic plants is very important during the process of offspring reproduction. In this study, the stability and heritability of At D-CGS has been analyzed in the transgenic lines Zongzuo CGS-ZG11 from the expression level, transcriptional level, translational level and characters level. Zigongdongdou, the At D-CGS transgenic acceptors, is a photoperiod-sensitive late-flowering cultivar from zigong, Sichuan. It is unsuitability for being grown in the main soybean producing region Huanghuai and dongbei, so in our study, the hybridized combination CGS J14898 was generated from At D-CGS transgenic plants zhongzuo CGS-ZG11 and conventional variety shidou 5 combining with marker-assisted selection and conventional breeding methods.The main results were as follow:(1) The exogenous gene At D-CGS has been integrated into the transgenic acceptors and can be stably inherited. A single copy of At D-CGS was inserted into the recipient plants and can be stably inherited in the three consecutive generations of the transgenic plants.(2) At D-CGS can be stably expressed at the transcriptional level in three consecutive generations of the transgenic plants. Its expression level in seeds is higher than in shoots, leaves and roots. At D-CGS can also be expressed stably at the transcriptional level.(3) The total methionine content of soybean seeds has been increased significantly in T6, T7 and T8 generation of transgenic plants, and this characters can be stably inherited in the threeconsecutive generations of the transgenic plants.(4) New soybean lines such as CGS14J898 has been cultivated by the hybridization of our transgenic soybean with high Met content and the conventional variety with excellent comprehensive characters. The content of Met increased significantly and the comprehensive characters are excellent in these new lines, therefore, they can be used as intermediate parents in the high methionine soybean breeding.(5) In the hybrids between transgenic soybean and the conventional variety, At D-CGS was expressed and Met content was increased significantly. This result indicated that At D-CGS can be expressed and inherited stably in different environment and genetic background.In this study, we confirmed that At D-CGS can be expressed and inherited stably in the transgenic plants, nither gene loss nor gene silencing occurred in the transgenic plants offspring. This transgenic material with enhanced Met content provides valuable experience and materials in the study of quality improvement in soybean. Transfering the exogenous gene to other improved varieties by backcrossing is meaningful in the breeding work: on the one hand, it is beneficial to cultivating the new transgenic cultivars with outstanding target character and excellent comprehensive characters, on the other hand, it can solve the problem due to the genotype restriction to some extent.