Medicinal Plant Research 2024, Vol.14, No.4, 223-233 http://hortherbpublisher.com/index.php/mpr 230 7.3 Combined salinity and oxidative stress on metabolite diversity The combined effects of salinity and oxidative stress on Ganoderma lucidumlead to a diverse array of secondary metabolites. Salicylic acid (SA) and calcium ions (Ca2+) have been shown to influence the biosynthesis of polysaccharides and triterpenoids. While Ca2+ alone does not affect polysaccharide and triterpenoid production, SA increases triterpenoid content by 23.32%. The combined induction of SA and Ca2+ results in a 9.02% increase in polysaccharide content and a 13.61% increase in triterpenoid content. This combined stress enhances the expression of key biosynthetic genes, such as ugp, pgm, and gls for polysaccharides, and hmgr, hmgs, mvd, fps, sqs, and ls for triterpenoids, across different developmental stages of G. lucidum(Ye et al., 2018). 8 Biotechnological Applications of Stress-Induced Metabolites 8.1 Industrial relevance of stress-enhanced metabolites in pharmaceuticals Ganoderma lucidum, a well-known medicinal mushroom, produces ganoderic acid (GA), a secondary metabolite with significant pharmacological activities. Environmental stressors such as water stress, heat stress, and nitrogen limitation have been shown to enhance the production of GA, making these stress-induced metabolites highly relevant for pharmaceutical applications. For instance, water stress increases intracellular reactive oxygen species (ROS) levels, which in turn boosts GA content significantly (Zhu et al., 2022). Similarly, heat stress not only induces the accumulation of GA but also enhances the expression of heat shock proteins (HSPs), which are crucial for the organism's stress response (Liu et al., 2018b; Zhang et al., 2018). Nitrogen limitation also promotes GA synthesis by activating specific transcription factors like GCN4, which regulate antioxidant enzyme biosynthesis to manage ROS levels (Lian et al., 2021). These findings highlight the potential of leveraging environmental stress to enhance the production of valuable secondary metabolites for pharmaceutical use. 8.2 Optimization strategies for large-scale cultivation of Ganoderma lucidum To optimize the large-scale cultivation of Ganoderma lucidum for enhanced metabolite production, several strategies can be employed. Liquid superficial-static culture (LSSC) has been identified as a superior method for producing higher GA content compared to submerged culture (SC) (Wang et al., 2020). Additionally, the manipulation of environmental conditions such as temperature and nutrient availability can significantly impact metabolite production. For example, the addition of calcium ions to the culture medium has been shown to enhance GA production through the calcineurin signal transduction pathway (Xu and Zhong, 2012). Moreover, understanding the genetic and physiological responses of G. lucidum to various stressors can inform the development of more efficient cultivation techniques. For instance, the overexpression of genes involved in ROS management and secondary metabolite biosynthesis can be targeted to improve yield under stress conditions (Hu et al., 2019; Zhu et al., 2022). 8.3 Use of elicitors to stimulate metabolite production under controlled conditions Elicitors are substances that can stimulate the production of secondary metabolites in fungi under controlled conditions. In Ganoderma lucidum, various elicitors such as ethylene, calcium ions, and ROS scavengers have been shown to enhance GA production. Exogenous ethylene, for example, increases both endogenous ethylene and GA levels by up-regulating genes involved in key metabolic pathways (Meng et al., 2022a). Calcium ions also act as effective elicitors by activating the calcineurin signal transduction pathway, which up-regulates the expression of genes involved in GA biosynthesis (Xu and Zhong, 2012). Additionally, the use of ROS scavengers like N-acetyl-l-cysteine (NAC) and ascorbic acid (VC) can modulate the oxidative stress response, thereby influencing GA production (Liu et al., 2018b; Hu et al., 2019). These elicitors provide a valuable tool for optimizing metabolite production in G. lucidumunder controlled cultivation conditions. 9 Future Prospects 9.1 Advancements in genetic engineering to enhance stress resilience and metabolite production The application of genetic engineering techniques has shown significant promise in enhancing the stress resilience and secondary metabolite production in Ganoderma lucidum. The development of genome-scale metabolic models (GSMM) such as model iZBM1060 has provided a comprehensive framework for understanding and manipulating metabolic pathways. For instance, the addition of phenylalanine was found to significantly increase
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