**7. References**

122 Soybean – Genetics and Novel Techniques for Yield Enhancement

defense against attack by tobacco hornworm (Li et al. 2003). Recently it was reported that silencing of the three soybean GmFAD3 genes enhanced the accumulation of *Bean Pod mottle virus* (BPMV) in plant tissues and enhanced susceptibility to virulent *Pseudomonas syringae*  bacteria (Singh et al. 2011). Silenced plants exhibited increased levels of jasmonic acid and slightly reduced levels of 18:3 indicating that loss of microsomal ω-3 activity enhances

Stearoyl-ACP-desaturase, omega-6, and omega-3 desaturases are diiron cofactor, histidine box motif enzymes that introduce, respectively, the first, second or third double bond into the specific C18 fatty acid substrate to yield oleate (18:1), linoleate (18:2), or linolenate (18:3). The expression and activity of these enzymes significantly determines the fatty acid composition and overall quality of soybean oil, and also contributes to the physiological adaptation to environmental temperature and the induction of defense responses to pathogens. Investigations of the regulation of desaturase expression and activity by temperature and pathogens in soybean are relatively recent, but initial findings suggest similarities with *Arabidopsis* and other plants. Down regulation of the *SACPD* gene expression results in plants with reduced 18:1, elevated 18:0, the formation of spontaneous lesions, increased salicylic acid accumulation, and constitutively expressed pathogenesisrelated genes (Kachroo & Kachroo 2009). These plants exhibit enhanced resistance to bacterial and oomycete pathogens. In both soybean seed and leaf tissues, the levels of 18:2 and 18:3 gradually increase as temperature decreases, but the transcript levels of the omega-6 desaturases do not increase at low temperature, suggesting that post-translational regulatory mechanisms likely play an important role in modulating the omega-6 (FAD2-1) enzyme activities. Transcript expression of the omega-3 desaturases *FAD8* and *FAD3* do change in response to changes in ambient temperature. *FAD8* is cold-inducible and the increased 18:3 level in chloroplast membranes due to upregulated *FAD8* expression is associated with low temperature tolerance. Upregulation of *FAD7* and increased 18:3 levels in chloroplasts modulate plant defense responses to pathogens through increased production of oxylipin antimicrobial and signaling molecules. SACPD, ω-6, and ω-3 fatty acid desaturase genes are present as multiple copies in the soybean genome as expected given the evidence (Schmutz et al. 2010, Ha et al., 2010) from cytogenetics, genetic mapping, and genomic sequencing that soybean is a paleopolyploid species that underwent at least two major genome duplications. The soybean genome possesses tissue-specific alleles for all three of C18 desaturase enzymes involved in the biosynthesis of triacylglycerols. The occurrence of seed-specific alleles of these genes provides for the accommodation of the great increase in lipid biosynthesis that occurs as the developing soybean seeds produce storage lipid reserves (Tang et al., 2005). Genomic (Schmutz et al., 2010) and gene expression analysis (Upchurch & Ramirez, 2010) using the Williams 82 soybean genome database is expected to expand knowledge of soybean gene regulatory sequences and their interaction with transcription complexes. Development of soybean SNP markers (Ha et al., 2010), mapping and dissection of Quantitative Trait Loci (Bachlava et al., 2008, Bachlava et al., 2009A, Bachlava et al., 2009B) and gene silencing analyses (Singh et al., 2011) may lead to the discovery of new genes for fatty acid biosynthesis and stress adaptation, and the potential epigenetic interactions between them. Since the capacity to induce host pathogen defenses is associated with specific desaturase-mediated changes in the levels of unsaturated C18 fatty

jasmonate accumulation and thereby susceptibility to *BPMV* in soybean.

**5. Conclusions** 


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**7** 

*Italy* 

**Genetically Modified Soybean** 

Piccolo Vincenzo and Infascelli Federico

Tudisco Raffaella, Calabrò Serena, Cutrignelli Monica Isabella,

*Department of Animal Science and Food Control; University of Naples; Naples* 

In recent years, genetically modified (GM) plants, whose DNA has been changed using genetic engineering techniques, are mainly used as foods for human and feeds and foods for farm animals. To date, a number of GM products have been approved for human consumption but concerns over safety persist, mainly as regards either the detection of transgenic plant genes and proteins in animal systems or allergenicity and toxicity of GM

Since their commercial release in 1996, the global cultivation area dedicated to the production of GM plants has increased significantly (ISAAA, 2010). The majority of GM crops currently produced, like soybean, corn, cotton and canola, have been engineered to enhance agronomic performance by transformation with genes encoding herbicide tolerance and pest resistance. GM soybean has been rendered tolerant to the glyphosate family of herbicides through expression of transgenic DNA from the CP4 strain of *Agrobacterium tumefaciens* that encodes 5-enolpyruvylshikamate-3-phosphate synthase (CP4 EPSPS). Roundup Ready (RR) soybean have been grown commercially from 1996 and continued to be the principal biotech crop in 2010. Farm animals are currently fed soybean and soybean meal developed from genetic transformation as well as corn and corn products. The European Union imports soybean from USA, Brazil, and Argentina, the main users of biotech crops globally. About 90% of the compound feed produced in the EU contains GM

Although regulations with regard to GM plants have been developed primarily from the perspective of human consumption of GM food, it is generally assumed that these criteria are suitable for a risk assessment of the consumption of GM feed by livestock. The protocol for establishing "substantial equivalence" of GM plant compared to isogenic parental lines does not complete a nutritional safety assessment of a GM plant, rather, it provides a starting point for the overall assessment (FAO/WHO, 2000). Based on the European novel food and feed regulation, all foods and feeds containing or derived from approved GM products in amounts greater than a 0.9% threshold are subject to labelling rules (European Commission, 2003). Labelling of feeds containing GM ingredients gives farmers the choice of using such feed for their livestock. However, products such as milk, meat, and eggs, that are derived from livestock fed transgenic feeds are exempt from EU-labelling laws. Several studies have been conducted to evaluate the safety of GM crops, but there is still a debate on

the risk of GM consumption and their potential passage into tissues.

**1. Introduction** 

plants.

soybean.

**in Animal Nutrition** 

desaturase enhances thermal tolerance, *Journal of Integrative Plant Biology* Vol. 52 (No. 6): 568-577.

