**2. Importance of soybean**

**1. Introduction**

18 Transgenic Crops - Emerging Trends and Future Perspectives

are highly required [3].

recalcitrant.

Soybean (*Glycine max* L.) is an important leguminous pulse crop grown for the production of oils and proteins. The legumes include cowpea, lentils, peas, peanuts and other pod producing plants that are cultivated commercially or privately for nutritional, pharmaceutical or industrial purposes. These plants have played a crucial role in the traditional diets of many countries including Brazil, China, India and regions in the Middle East and South America [1]. In contrast, many African and European countries do not fully benefit from the subsistent and commercial cultivation of soybean. The less significant role of soybean in these regions may be due to the poor growth conditions. The growth and productivity of this crop has been adversely affected by the biotic and abiotic stress factors [2]. Even though it has the potential to become a major crop in less cultivated regions (Africa and Europe) because of its many uses (as feed, food, etc.), plant modifications to increase yields

The genetic modification techniques such as the *Agrobacterium*-mediated genetic transformation, electro and chemical cell surface poration or direct protoplast-mediated DNA transfer need to be used to improve the agro-economic traits of this crop in those regions. *Agrobacterium tumefaciens* is a gram-negative soil borne bacterium, which infect dicotyledonous plants, causing a crown gall disease. The crown gall tumour is formed around the wound sites, creating a reservoir for its infestation [4]. The procedure for plant transformation takes advantage of this natural infecting ability to transfer the tumour-inducing plasmid (Ti-plasmid) into hosts. The plasmid DNA is naturally found within the bacterium, and is exploited for transformation with foreign DNA segments of interest obtained from different sources. The genes of interest could be introduced into the host plant's genome during bacterial infection. This phenomenon is known as genetic transformation, whereby the Ti-plasmid expression and integration of the transfer DNA (cloned segment of DNA transferred into hosts) within the host plant

The first tissue culture based *in vitro* genetic transformation using this approach was reported by Hinchee et al. [6]. Subsequently, numerous reports emerged including those of Chee et al. [7], Yan et al. [8], Shi-Yun [9], Olhoft et al. [10] and Homrich et al. [11] on the use of *A. tumefaciens* to introduce agro-economic traits such as the resistance to pests (*Bt* crops), enhanced protein quality and drought stress tolerance in soybean. This chapter provides a review on the factors affecting *Agrobacterium*-mediated transformation, and gives an account on the outcomes obtained during the valuation of factors that cause recalcitrance during genetic transformation of soybean. The study provides a thorough analysis of the organogenic and phenotypic responses that occur due to the tissue culture conditions and the amenability of genotypes to *Agrobacterium* infection. The application of antimicrobials, plant growth regulators, culture media, bacterial density and the type of explants used influence the transformation efficiency of soybean. Optimised routine strategies in the transformation of soybean are still a prerequisite, since this crop is highly considered

genome can also be inherited by the offspring of the host [5].

Soybean plays a critical role in world agriculture, providing about 40% proteins, 20% oil and 30% carbohydrates contained within the seeds. This crop serves as the cheapest and profitable form of oilseed worldwide for many producers, especially small holder poultry farmers [5]. The industrial processing of this crop to manufacture high protein rich feeds for livestock, pigs and fish farms is growing immensely. The use of soybean in the production of edible oil and biodiesel as a green alternative fuel is also expanding [6]. In human nutrition and health, soybean meals have proved to reduce the cause of several acute and chronic conditions. Messina [1] reported the improvement of body calcium retention lowering urinary calcium excretion after the use of soy-proteins compared to consumption of a mixture of animal proteins. **Table 1** provides information regarding the estimated amount of seed yields used for industrial processing, meal manufacturing and some of the pharmaceutical products derived from soybeans.

Following the drought because of El Nino-related conditions in the sub-Saharan Africa, soybean yield prospects for 2017/2018 have deteriorated, including productions in South America and Southeast Asia. The lowering projections will influence manufacturing and processing of soybean products for many industries and human consumption. Soybeans were also found to contain low fats (approximately 5%), easily modulated trypsin inhibitors and other compounds considered as non-nutritive components. Some of these compounds like phytate were considered to reduce mineral bioavailability of beans but, it has been postulated that phytic acid also lowers the risk of colon and breast cancer [7]. Soybean is considered an excellent source of iron, zinc and folate which serve as essential nutrients and reduce the risk of neural tube defects in humans and promote efficient uptake of vitamin C [8, 9].

Among all the legumes, soybeans are unique because they are a concentrated source of isoflavones that naturally reduce the risk of cancer and heart disease [1]. In addition, soybeans also contain cysteine proteases protein enzymes. These are one of the group of proteolytic enzymes that catalyse the hydrolysis of various polypeptide substrates for the production


**Table 1.** Soybean producing areas, yield estimates and consumption/processing on industrial scale.

and assembly of proteins that get remobilised or degraded [10]. Proteases are well known for their key role in biochemical processes, implicated for the development and continuation of several diseases. Their role in disease formation, especially during programmed cell death (PCD) involves dismantling of organelles and the different macro molecules required for plant growth and development. They are largely involved in translation and folding of storage proteins, protein remobilisation, signalling controls and at lesser extent for morphogenesis [11].

have been met with very limited transformation efficiencies [21]. Another method is particle bombardment invented by John Sanford [22]. This microprojectile or biolistic bombardment employs particle acceleration coated DNA into the target plant tissues. Once in the cells, the DNA becomes permanently integrated into the chromosomes of the host plant genome [20]. Although, there are numerous techniques used for transformation, all methods face the same challenges of inefficiency, lack of a routinely used protocol and the genotype specificity problem.

The Role of Plant Genotype, Culture Medium and *Agrobacterium* on Soybean Plantlets…

http://dx.doi.org/10.5772/intechopen.78773

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There are several challenges faced during the process of delivering segments of oncogenic DNA to susceptible plant cells. The limitations are mostly associated with *in vitro* culture conditions than the genetic transfer and expression. Plant regeneration *in vitro* can be efficiently and rapidly achieved for plantlets micropropagation. Soybean has been successfully regenerated through adventitious/axillary/meristem shoot organogenesis and direct or indirect somatic embryogenesis using different types of mature and immature explants. But, coupling *in vitro* plant tissue culture with transformation to improve production of transgenic plants presents its own challenges. To produce transformants, especially in soybeans, *in vitro* culturing strategies that are highly efficient are required. Soybean is still considered a recalcitrant crop, and the nature of culture media and susceptibility of selected explants to *Agrobacterium*

Constraining factors such as; genotype specificity, antibiotics toxicity, selection pressure, explant type and age, *Agrobacterium* overgrowth and contaminations are still being neglected. Zia [23] indicated that, these abovementioned factors play a key developmental role in *in vitro* manipulation of plants. Failure of many tissue culture based *in vitro* transformations is mainly due to these factors. In addition, other forms of transformation like electroporation, particle bombardment and protoplast-mediated transformation pose more challenges than *Agrobacterium*-mediated genetic transformation under *in vitro* culture conditions. These techniques are expensive to carry-out, are labour intensive with prolonged steps of transformation, cause unstable transgene expression particularly due to gene silencing [24], produce multiple transgene copy number [12] and cause gene rearrangement within inserts and insta-

Plant transformation has become the most important and reliable technology for the improvement of many crop cultivars, as well as for studying gene functions in plants. In soybean, the technique has already been used to produce genetically modified plants. The genetically modified soybeans range from metabolically engineered plants such as those exhibiting increased oleic acid as well as the herbicide-tolerant (HT) cultivars [26, 27]. Soybean transformation led to production of elite cultivars, increased gene pool, plants with improved secondary metabolites and production of disease free plants, especially regenerated under aseptic culture conditions [2, 28]. As the attempts in soybean transformation progresses, procedures must focus on transgenic plant production exhibiting tolerance to abiotic stress factors. This is so, because soybean growth and productivity is severely hampered by abiotic

**3.2. Challenges faced during genetic transformation**

influences transgenic plant regeneration efficiency.

bility over the generation of transgenic plants [25].

**4. Role of genetic transformation in soybean improvement**
