**3. Transgenic breeding in soybean improvement**

Transgenic soybeans are one of the few vegetable-based foods that contain all nine necessary amino acids. As a result, the transgenic soybean has grown in importance as a human and animal protein source, with 85% of its production going to animal feed, and the rest is going to direct human consumption [55]. Transgenic crops have been embraced by key soybean-growing countries such as the United States, Brazil,


#### **Table 1.**

*Details of marker-assisted breeding conducted for improvement of soybean for various traits.*

#### *Soybean Molecular Design Breeding DOI: http://dx.doi.org/10.5772/intechopen.105422*

and Argentina, and they now account for about 85–95% of total soybean in terms of crop harvested area. The major markets for genetically modified agricultural seeds are North America and South America, which together account for more than 90% of the global GM seed industry. Nearly 85–95% of the soybean crop grown in North and South America is genetically modified. Demand for America's produced corn and soybean produce from other countries (particularly China) is a major factor in determining planted acreage and seed demand [56].

The landmark products of transgenic soybean's genetic composition allow it to be used for a wide range of purposes, which keeps it in high demand. Initially, manufacturers only wanted to use transgenics to grow more soy at a low cost in order to meet this demand, as well as to fix any problems in the growing process. But eventually it was discovered that soybean can be genetically modified to contain healthier components or even focus on one aspect of the soybean to produce in larger quantities. The first and second generations of genetically modified (GM) foods were named after these periods. The benefits of first-generation GM foods were oriented toward the manufacturing process and companies, whereas the second generation of GM foods offers a variety of advantages and added value for the consumer, including improved nutritional composition or even therapeutic effects [57]. The main and important landmark products of soybean are Roundup ready soybean, Generic GMO soybean, and genetic modification in soybean to improve soybean oil. Roundup Ready soybeans (the original variety was also known as GTS 40–3-2 (OECD UI: MON-04032-6)) are a series of glyphosate-resistant soybean cultivars developed by Monsanto. Glyphosate is a herbicide that kills plants by interfering with the production of phenylalanine, tyrosine, and tryptophan, which are all necessary amino acids. These amino acids are referred as "essential" since only plants and microorganisms can produce them, and mammals are dependent on the plants for these amino acids [58].

Soybean transgenic technology is an essential tool for validating the soybean gene function. Soybean genetic transformation has been explored for over two decades, but progress has been slow and inefficient, which is why some studies used Arabidopsis instead of soybean for functional validation. Several transformation systems have been developed, including shoot meristems [59], hypocotyls ([60], embryo [61], immature cotyledons, half-seed explants [62, 63], and cotyledonary nodes [64]. Agrobacterium-mediated cotyledonary node (CN) soybean transformation is currently widely employed due to its ease of usage, reproducibility, quantity of copies of foreign DNA, and low cost of experimentation [63, 65]. The overall average efficiency of transformation was 3.8–8.7% [63, 64]. Recently, the average transformation efficiency of soybean had been improved to 18.7% [66]. However, it is still lower than the 23% as reported in rice [67] and more than 30% found in maize [68].

Seed sterilization and germination followed by Agrobacterium infection, cocultivation of soybean explants and Agrobacterium, shoot induction, shoot elongation, rooting, and finally, moving the plants to pots containing soil are the different steps involved in the general transformation process. Many factors affect the transformation efficiency at the above different steps. For example, the soybean genotypes used in the transformation are the initial effector. The transformation efficiency and regeneration rate of 20 soybean varieties have been studied, and it was reported that transformation efficiency varied greatly (0.31–4.59%) among the different genotypes [69]. Second, all Agrobacterium concentrations, soybean explant status, Agrobacterium suspension medium, and cocultivation time will affect the infection efficiency during the Agrobacterium infection process, which is one of the most

significant processes. Explant regeneration is another important factor in affecting transformation efficiency. Plant hormone has been found to have a vital function in promoting explant regeneration, and the right dose could boost efficiency [64]. Previously research studies have showed that the combination of L-glutamine and L-asparagine in culture media increases the transformation efficiency by inhibiting *GmPRs* expression [70].
