Abstract: Soybean [Glycine max (L.) Merr.] is the genetically modified (GM) crops that is earliest commercially planted on large scale. GM soybean is retaining its position as the GM crop occupied the largest scale globally with food, nutritional, industrial, and pharmaceutical uses. From 1996 to 2012, total 763.1 million hectares GM soybean had been planted and by growing GM soybean, almost 37 billion US dollars income was brought to farmers. In 2013, about 84.5 million hectares of GM soybean were planted around the world in 11 countries which accounted for 48% of all the GM crops hectarage and 79% for soybean grown all over the world. Though herbicide-resistant transgenic soybean holds a leading market share in the world, soybean has been regarded as a recalcitrant crop to be transformed for many years. Efficient and stable transformation is a restrictive factor for production of transgenic soybean and gene function research. The most widely and routinely used transformation systems are cotyledonary node-Agrobacterium-mediated transformation and somatic embryo-particle-bombardment-mediated transformation. The first fertile transgenic soybean plants were produced nearly simultaneously by these two methods in 1988. Even after more than two decades, these two methods have continued to be improved and have produced most transgenic soybean plants. The transformation efficiencies of these improved protocols have been extended and the system was successfully adapted to embryogenic suspension cultures for the regeneration of fertile transgenic soybean plants. These ready systems enable us to improve agronomic characteristics or to analyze gene function in soybean by transgenic approaches. In this review, recent advances and problems in research of soybean transformation system were described, with a focus on the characteristics of soybean regeneration systems such as organogenesis, somatic embryogenesis and protoplasts system. The representative soybean transformation systems mediated by Agrobacterium tumefaciens and particle bombardment have been summarized, and described their experimental parameters such as soybean genotype, explant, regeneration system, screening system, transformation frequencies. Analysis suggests that the genotype, explant type and so on can be used in the transformation of soybean has been developed and the transformation frequencies has been improved significantly. Some reports showed higher transformation efficiency over 10% and even some over 30% in some cases. However, the date of transformation frequencies had been obtained in some research reports that involved small sample size. The transformation frequencies between different experimental replications often repeated differences greatly. Sometimes, obtained high transformation frequencies in the single factor experiment, often doesn’t get well again in multi-factor integrated experiment. It indicated that the transformation efficiency still is affected by some unknown factors that is hard to control. On the other hand, the transformation efficiency still relies on the skill of the technicians and on the tissue culture conditions of the laboratory. That leads to some problems such as the same transformation process is poor in reproducibility between laboratories, the transformation frequencies are greatly different between operators, the transformation frequencies are not stable in the same laboratory. And those problems hindered the establishment of high-throughput transformation systems for soybean. Meanwhile, the research result of soybean transformation and transgenic lines was reviewed, and the current transgenic lines for soybean breeding in China were surveyed. Further, some new genetically modified technologies used in soybean were prospected, such as genome editing techniques and precise genome modification techniques.

Key words: soybean [Glycine max (L.) Merr.], transgenic system, transformation efficiency, Agrobacterium tumefaciens, particle bombardment