Journal of Energy Bioscience 2024, Vol.15, No.6, 378-387 http://bioscipublisher.com/index.php/jeb 384 the IFS2 and CHS8 gene promoters. The study by Chu et al. in 2017 showed that overexpression of GmMYB29 in soybean hairy roots increased isoflavone content, while RNAi-mediated silencing led to reduced isoflavone levels. In addition, the expression of isoflavone biosynthesis genes can also be affected by the environment. For example, soybean varieties such as Hefeng 25 and Sfera have increased isoflavone content under adverse climatic conditions (Veremeichik et al., 2020). These research results are conducive to the selection and genetic manipulation of soybean genotypes to improve isoflavone content. 7.2 Role of isoflavones in plant defense mechanisms Isoflavones can act as phytoalexins in leguminous plants such as soybeans, compounds synthesized in response to pathogen attacks, thereby enhancing plant disease resistance and playing an important role in plant defense mechanisms. Soybean roots can secrete isoflavones such as daidzein and genistein, which can affect rhizosphere interactions, including inducing symbiosis with rhizobia (Sugiyama et al., 2017). Under stress conditions (such as the application of methyl jasmonic acid), the expression of isoflavone biosynthesis genes increases, which can further enhance their role in plant defense. Jeong et al. found in 2018 that methyl jasmonic acid treatment can significantly upregulate genes involved in the isoflavone biosynthesis pathway, increase isoflavone production, and enhance plant defense capabilities. 7.3 Isoflavones as functional nutraceuticals Isoflavones can promote human health and are valuable functional nutrients. Sohn et al. (2021) demonstrated that isoflavones can reduce the incidence of hormone-related cancers, osteoporosis, menopausal symptoms, and cardiovascular diseases (Figure 3). Metabolic engineering of isoflavone biosynthesis has important agronomic and nutritional significance for both leguminous and non-leguminous crops. In Arabidopsis, the expression of soybean isoflavone synthase can produce the isoflavone genistein, indicating that it can increase the dietary isoflavone content of various crops (Jung et al., 2000). Yuk et al. (2016) and Kumar et al. (2021) treated soybeans with ethylene and other signaling molecules (such as serotonin and melatonin) to regulate the accumulation of isoflavones in soybeans. Advances in metabolic engineering and regulation of isoflavone biosynthesis pave the way for the development of healthy crops. Figure 3 Natural role of isoflavones in plants and environmental interactions (Adopted from Sohn et al., 2021) 8 Biotechnological Advances in Isoflavone Engineering 8.1 Genetic engineering approaches for isoflavone biosynthesis Genetic engineering plays a key role in the biosynthesis of soybean isoflavones. Its main principle is to activate phenylpropanoid pathway genes by expressing maize C1 and R transcription factors in soybean seeds to increase the level of soybean isoflavones. Co-inhibition of flavanone 3-hydroxylase, which blocks the anthocyanin branch
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