Medicinal Plant Research 2024, Vol.14, No.4, 223-233 http://hortherbpublisher.com/index.php/mpr 228 aquaporin (GlAQP) and NADPH oxidase (NOX) (Zhu et al., 2022). Additionally, metabolomic studies under heat stress have shown the accumulation of phosphatidic acid (PA), which is involved in the regulation of secondary metabolism through phospholipid signaling (Liu et al., 2017b). These analyses provide a comprehensive view of the biochemical changes that occur in response to stress. 5.3 Integration of multi-omics for comprehensive insights The integration of multi-omics approaches, including genomics, transcriptomics, proteomics, and metabolomics, offers a holistic understanding of the stress response in Ganoderma lucidum. For instance, a combined transcriptomic and metabolomic analysis under ethylene treatment revealed the coordinated regulation of genes and metabolites involved in the TCA cycle and ganoderic acid biosynthesis (Meng et al., 2022a). Similarly, the integration of transcriptome and metabolome data during the development of G. lucidum identified key transcription factors and metabolic pathways involved in GA biosynthesis (Meng et al., 2022b). These integrated approaches enable the identification of regulatory networks and key molecular players that mediate the stress response, providing comprehensive insights into the adaptive mechanisms of G. lucidum under environmental stress. 6 Stress-Induced Changes in Key Metabolites 6.1 Impact of temperature stress on triterpenoid biosynthesis Temperature stress, particularly heat stress (HS), has been shown to significantly influence the biosynthesis of triterpenoids, such as ganoderic acids (GA), in Ganoderma lucidum. HS induces the accumulation of reactive oxygen species (ROS), which in turn regulates the expression of heat shock proteins (HSPs) and enhances GA biosynthesis. For instance, HS treatment increases the length between hyphal branches and induces GA accumulation, which is mitigated by ROS scavengers like NAC and VC (Liu et al., 2018b). Additionally, membrane fluidity plays a crucial role in HS-induced GA biosynthesis. Increased membrane fluidity, induced by HS, is associated with elevated GA levels, and this effect can be reversed by membrane rigidifiers such as DMSO (Liu et al., 2017a). Furthermore, phospholipid-mediated signal transduction, particularly involving phosphatidic acid (PA) and phospholipase D (PLD), is essential for HS-induced GA biosynthesis (Liu et al., 2017b). The AMP-activated protein kinase (AMPK)/Sucrose-nonfermenting serine-threonine protein kinase 1 (Snf1) pathway also participates in this process by mediating metabolic rearrangements in response to HS, thereby influencing GA production (Hu et al., 2019). 6.2 Oxidative stress and its effects on polysaccharide production Oxidative stress, characterized by elevated levels of ROS, significantly impacts the production of polysaccharides in G. lucidum. Under oxidative stress conditions, the balance of ROS is crucial for the regulation of secondary metabolite pathways. For example, water stress, which induces oxidative stress, increases intracellular ROS levels and subsequently enhances ganoderic acid content and NADPH oxidase (NOX) activity. The cross-talk between aquaporin (GlAQP) and NOX modulates ROS levels, thereby regulating GA biosynthesis under water stress (Zhu et al., 2022). Additionally, the role of calcium signaling in oxidative stress response is noteworthy. Calcium ions (Ca2+) and their associated signaling pathways, such as the calcineurin pathway, are involved in the regulation of GA biosynthesis under oxidative stress conditions. The addition of Ca2+ enhances GA production, suggesting that calcium signaling is integral to the oxidative stress response and secondary metabolite regulation in G. lucidum (Xu and Zhong, 2012). 6.3 The role of combined stress factors in metabolite diversity The interplay of multiple stress factors can lead to a diverse array of secondary metabolites in G. lucidum. Combined stress factors, such as temperature and oxidative stress, can synergistically influence metabolite pathways. For instance, HS not only induces ROS accumulation but also increases cytosolic Ca2+ concentration, which is crucial for the regulation of hyphal branching, HSP expression, and GA biosynthesis (Zhang et al., 2016). The interaction between ROS and Ca2+ signaling pathways highlights the complexity of stress responses in G. lucidum. Moreover, the integration of transcriptomics and metabolomics analyses has revealed that ethylene, another stress factor, can modulate key metabolic pathways, including the tricarboxylic acid (TCA) cycle and
RkJQdWJsaXNoZXIy MjQ4ODYzNA==