Heat Stress Modulates Mycelium Growth, Heat Shock Protein Expression, Ganoderic Acid Biosynthesis, and Hyphal Branching of Ganoderma lucidum via Cytosolic Ca ²⁺

Abstract

Heat stress (HS) influences the growth and development of organisms. Thus, a comprehensive understanding of how organisms sense HS and respond to it is required. Ganoderma lucidum, a higher basidiomycete with bioactive secondary metabolites, has become a potential model system due to the complete sequencing of its genome, transgenic systems, and reliable reverse genetic tools. In this study, we found that HS inhibited mycelium growth, reduced hyphal branching, and induced the accumulation of ganoderic acid biosynthesis and heat shock proteins (HSPs) in G. lucidum. Our data showed that HS induced a significant increase in cytosolic Ca 2؉ concentration. Further evidence showed that Ca 2؉ might be a factor in the HS-mediated regulation of hyphal branching, ganoderic acid (GA) biosynthesis, and the accumulation of HSPs. Our results further showed that the calcium-permeable channel gene (cch)-silenced and phosphoinositide-specific phospholipase gene (plc)-silenced strains reduced the HS-induced increase in HSP expression compared with that observed for the wild type (WT). This study demonstrates that cytosolic Ca 2؉ participates in heat shock signal transduction and regulates downstream events in filamentous fungi. IMPORTANCEGanoderma lucidum, a higher basidiomycete with bioactive secondary metabolites, has become a potential model system for evaluating how environmental factors regulate the development and secondary metabolism of basidiomycetes. Heat stress (HS) is an important environmental challenge. In this study, we found that HS inhibited mycelium growth, reduced hyphal branching, and induced HSP expression and ganoderic acid biosynthesis in G. lucidum. Further evidence showed that Ca 2؉ might be a factor in the HS-mediated regulation of hyphal branching, GA biosynthesis, and the accumulation of HSPs. This study demonstrates that cytosolic Ca 2؉ participates in heat shock signal transduction and regulates downstream events in filamentous fungi. Our research offers a new way to understand the mechanism underlying the physiological and metabolic responses to other environmental factors in G. lucidum. This research may also provide the basis for heat shock signal transduction studies of other fungi. Ganoderma lucidum, a traditional precious medicinal mushroom, has been commonly used throughout China and Southeast Asia for many centuries as a home remedy for treating minor disorders and promoting vitality and longevity (1). Modern pharmacological and clinical research has demonstrated that G. lucidum has significant antitumor, antiviral, antihypertensive, and immunomodulatory activities (2, 3). These pharmaceutical activities come from the bioactive compounds of G. lucidum. In recent years, many of these biologically useful compounds, including ganoderic acids (GAs) and polysaccharides, have been isolated and characterized in G. lucidum (4,5). Ganoderic acids, also called triterpenoids, are one of the major secondary metabolites with pharmacological activity and are also known to be an important medicinal i...

Proteome and Transcriptome Reveal Involvement of Heat Shock Proteins and Indoleacetic Acid Metabolism Process in Lentinula Edodes Thermotolerance

“…S2 and Table S4). In Ganoderma lucidum, heat stress induced a significant increase in the cytosolic Ca 2+ concentration, regulating the accumulation of HSPs and downstream events in filamentous fungi [71]. In plants, it was reported that calcium-activated calmodulin (Ca 2+ -CaM) and calcium-dependent protein kinase (CDPK) were directly involved in the heat stress signal transduction pathway and up-regulated heatshock proteins (HSPs) under heat stress [72][73][74].…”

Membrane fluidity is involved in the regulation of heat stress induced secondary metabolism in Ganoderma lucidum

“…Previous studies have demonstrated that HS can enhance GA biosynthesis (Zhang et al ., ). To further study the relationship between membrane fluidity and GA biosynthesis, we examined the effect of the membrane fluidizer BA and membrane rigidifier DMSO, which are used to increase and decrease the lipid bilayer's membrane fluidity, respectively (Suri and Dhindsa, ; Saidi et al ., ), during GA biosynthesis.…”

“…As shown in Fig. B, HS‐treated‐only strains led to an increase ( P < 0.05) of approximately 1.7‐fold in the GA content compared with the non‐HS treatment, which was consistent with previous reports ( Z hang et al ., ). The addition of different concentrations of DMSO alleviated this increase.…”

“…Further studies determined that several chemical inducers, such as methyl jasmonate (Ren et al ., ), phenobarbital (Liang et al ., ), acetic acid (Ren et al ., ) and H 2 O 2 (Zhang et al ., ), could improve GA biosynthesis. Our preliminary study also proved that heat stress can lead to a significant increase in GA biosynthesis (Zhang et al ., ). Although much of work has been conducted on GA biosynthesis induced by extracellular environmental change and several mechanisms have been reported, research on the related mechanism still lags behind.…”

“…In the model microorganism Thermococcus kodakarensis KOD1, heat stress induces the upregulation of proteins, identified through MALDI‐TOF/MS, related to secondary metabolite synthesis by KEGG pathway analysis (Jia et al ., ). Our recent research also showed a significant increase in GA content after HS in G. lucidum (Zhang et al ., ). Combined, these results indicate that HS can result in changes in secondary metabolism.…”