Glsnf1-mediated metabolic rearrangement participates in coping with heat stress and influencing secondary metabolism in Ganoderma lucidum

Hydrogen sulfide maintains mitochondrial homeostasis and regulates ganoderic acids biosynthesis by SQR under heat stress in Ganoderma lucidum

Hydrogen sulfide (H2S) has recently been recognized as an important gaseous transmitter with multiple physiological effects in various species. Previous studies have shown that H2S alleviated heat-induced ganoderic acids (GAs) biosynthesis, an important quality index of Ganoderma lucidum. However, a comprehensive understanding of the physiological effects and molecular mechanisms of H2S in G. lucidum remains unexplored. In this study, we found that heat treatment reduced the mitochondrial membrane potential (MMP) and mitochondrial DNA copy number (mtDNAcn) in G. lucidum. Increasing the intracellular H2S concentration through pharmacological and genetic means increased the MMP level, mtDNAcn, oxygen consumption rate level and ATP content under heat treatment, suggesting a role for H2S in mitigating heat-caused mitochondrial damage in G. lucidum. Further results indicated that H2S activates sulfide-quinone oxidoreductase (SQR) and complex III (Com III), thereby maintaining mitochondrial homeostasis under heat stress in G. lucidum. Moreover, SQR also mediated the negative regulation of H2S to GAs biosynthesis under heat stress. Furthermore, SQR might be persulfidated under heat stress in G. lucidum. Thus, our study reveals a novel physiological function and molecular mechanism of H2S signalling under heat stress in G. lucidum with broad implications for research on the environmental response of microorganisms.

GlMPC activated by GCN4 regulates secondary metabolism under nitrogen limitation conditions in Ganoderma lucidum

IMPORTANCE

Mitochondrial pyruvate carrier (MPC) is a pyruvate transporter that plays a crucial role in regulating the carbon metabolic flow and is considered an essential mechanism for microorganisms to adapt to environmental changes. However, it remains unclear how MPC responds to environmental stress in organisms. General control non-derepressible 4 (GCN4), a key regulator of nitrogen metabolism, plays a pivotal role in the growth and development of fungi. In this study, we report that GCN4 can directly bind to the promoter region and activate the expression of GlMPC, thereby regulating the tricarboxylic acid cycle and secondary metabolism under nitrogen limitation conditions in Ganoderma lucidum. These findings provide significant insights into the regulation of carbon and nitrogen metabolism in fungi, highlighting the critical role of GCN4 in coordinating metabolic adaptation to environmental stresses.

The AMP-Activated Protein Kinase (AMPK) Positively Regulates Lysine Biosynthesis Induced by Citric Acid in Flammulina filiformis

Flammulina filiformis, the most produced edible mushroom species in China, is rich in lysine. Further enhancing its lysine biosynthesis is vital for improving its quality in industrialized cultivation. Citric acid induction significantly increases both the biomass and growth rate of F. filiformis hyphae, as well as the lysine content. The genes encoding enzymes in the lysine biosynthesis pathway were detected under the optimal induction, revealing that the expression levels of hcs, hac, and hah were 2.67, 1.97, and 1.90 times greater, respectively, relative to the control, whereas no significant difference was seen for hdh, aat, sr, and shd, and the expression of aar decreased. Furthermore, the transcriptional levels of Ampk, GCN2, GCN4, and TOR were found significantly upregulated, with the most upregulated, Ampk, reaching a level 42.68 times greater than that of the control, while the phosphorylation of AMPK rose by nearly 54%. In AMPK-silencing strains under the optimal induction, however, the phosphorylation increment dropped to about 16% and the lysine content remained at the same level as in the WT. Thus, AMPK is presented as the critical intermediary in citric acid's regulation of lysine biosynthesis in F. filiformis.

Effects of glutamate oxaloacetate transaminase on reactive oxygen species in Ganoderma lucidum

Nitrogen metabolism can regulate mycelial growth and secondary metabolism in Ganoderma lucidum. As an important enzyme in intracellular amino acid metabolism, glutamate oxaloacetate transaminase (GOT) has many physiological functions in animals and plants, but its function in fungi has been less studied. In the present study, two GOT isoenzymes were found in G. lucidum; one is located in the mitochondria (GOT1), and the other is located in the cytoplasm (GOT2). The reactive oxygen species (ROS) level was increased in got1 silenced strains and was approximately 1.5-fold higher than that in the wild-type (WT) strain, while silencing got2 did not affect the ROS level. To explore how GOT affects ROS in G. lucidum, experiments related to the generation and elimination of intracellular ROS were conducted. First, compared with that in the WT strain, the glutamate content, one of the substrates of GOT, decreased when got1 or got2 was knocked down, and the glutathione (l-γ-glutamyl-l-cysteinylglycine) (GSH) content decreased by approximately 38.6%, 19.3%, and 40.1% in got1 silenced strains, got2 silenced strains, and got1/2 co-silenced strains respectively. Second, GOT also affects glucose metabolism. The pyruvate (PA), acetyl-CoA and α-ketoglutarate (α-KG) contents decreased in got1 and got2 silenced strains, and the transcription levels of most genes involved in the glycolytic pathway and the tricarboxylic acid cycle increased. The NADH content was increased in got1 silenced strains and got2 silenced strains, and the NAD⁺/NADH ratio was decreased, which might result in mitochondrial ROS production. Compared with the WT strain, the mitochondrial ROS level was approximately 1.5-fold higher in the got1 silenced strains. In addition, silencing of got1 or got2 resulted in a decrease in antioxidant enzymes, including superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase. Finally, ganoderic acid (GA) was increased by approximately 40% in got1 silenced strains compared with the WT strain, while silencing of got2 resulted in a 10% increase in GA biosynthesis. These findings provide new insights into the effect of GOT on ROS and secondary metabolism in fungi. KEY POINTS: • GOT plays important roles in ROS level in Ganoderma lucidum. • Silencing of got1 resulted in decrease in GSH content and antioxidant enzymes activities, but an increase in mitochondrial ROS level in G. lucidum. • Silencing of got1 and got2 resulted in an increase in ganoderic acid biosynthesis in G. lucidum.

Mitochondrial pyruvate carrier influences ganoderic acid biosynthesis in Ganoderma lucidum

Mitochondrial pyruvate carriers (MPCs), located in the inner membrane of mitochondria, are essential carriers for pyruvate to enter mitochondria. MPCs regulate a wide range of intracellular metabolic processes, such as glycolysis, the tricarboxylic acid cycle (TCA cycle), fatty acid metabolism, and amino acid metabolism. However, the metabolic regulation of MPCs in macrofungi is poorly studied. We studied the role of MPCs in Ganoderma lucidum (GlMPC) on ganoderic acid (GA) biosynthesis regulation in G. lucidum. In this study, we found that the mitochondrial/cytoplasmic ratio of pyruvate was downregulated about 75% in GlMPC1- and GlMPC2-silenced transformants compared with wild type (WT). In addition, the GA content was 17.72 mg/g and increased by approximately 50% in GlMPC1- and GlMPC2-silenced transformants compared with WT. By assaying the expression levels of three key enzymes and the enzyme activities of isocitrate dehydrogenase (IDH) and α-ketoglutarate dehydrogenase (α-KGDH) of the TCA cycle in GlMPC1- and GlMPC2-silenced transformants, it was found that the decrease in GlMPCs activity did not significantly downregulate the TCA cycle rate, and the enzyme activity of IDH increased by 44% compared with WT. We then verified that fatty acid β-oxidation (FAO) supplements the TCA cycle by detecting the expression levels of key enzymes involved in FAO. The results showed that compared with WT, the GA content was 1.14 mg/g and reduced by approximately 40% in co-silenced transformants. KEY POINTS: • GlMPCs affects the distribution of pyruvate between mitochondria and the cytoplasm. • Acetyl-CoA produced by FAO maintains the TCA cycle. • Acetyl-CoA produced by FAO promotes the accumulation of GA.

Target of Rapamycin Mediated Ornithine Decarboxylase Antizyme Modulate Intracellular Putrescine and Ganoderic Acid Content in Ganoderma lucidum

Putrescine (Put) has been shown to play an important regulatory role in cell growth in organisms. As the primary center regulating the homeostasis of polyamine (PA) content, ornithine decarboxylase antizyme (AZ) can regulate PA content through feedback. Nevertheless, the regulatory mechanism of Put is poorly understood in fungi. Here, our analysis showed that GlAZ had a modulate effect on intracellular Put content by interacting with ornithine decarboxylase (ODC) proteins and reducing its intracellular protein levels. In addition, GlAZ upregulated the metabolic pathway of ganoderic acid (GA) biosynthesis in Ganoderma lucidum by modulating the intracellular Put content. However, a target of rapamycin (TOR) was found to promote the accumulation of intracellular Put after the GlTOR inhibitor Rap was added exogenously, and unbiased analyses demonstrated that GlTOR may promote Put production through its inhibitory effect on the level of GlAZ protein in GlTOR-GlAZ-cosilenced strains. The effect of TOR on fungal secondary metabolism was further explored, and the content of GA in the GlTOR-silenced strain after the exogenous addition of the inhibitor Rap was significantly increased compared with that in the untreated wild-type (WT) strain. Silencing of TOR in the GlTOR-silenced strains caused an increase in GA content, which returned to the WT state after replenishing Put. Moreover, the content of GA in GlTOR-GlAZ-cosilenced strains was also not different from that in the WT strain. Consequently, these results strongly indicate that GlTOR affects G. lucidum GA biosynthesis via GlAZ. IMPORTANCE Research on antizyme (AZ) in fungi has focused on the mechanism by which AZ inhibits ornithine decarboxylase (ODC). Moreover, there are existing reports on the regulation of AZ protein translation by TOR. However, little is known about the mechanisms that influence AZ in fungal secondary metabolism. Here, both intracellular Put content and GA biosynthesis in G. lucidum were shown to be regulated through protein interactions between GlAZ and GlODC. Furthermore, exploration of upstream regulators of GlAZ suggested that GlAZ was regulated by the upstream protein GlTOR, which affected intracellular Put levels and ganoderic acid (GA) biosynthesis. The results of our work contribute to the understanding of the upstream regulation of Put and provide new insights into PA regulatory systems and secondary metabolism in fungi.

Homokaryotic High-Quality Genome Assembly of Medicinal Fungi Wolfiporia hoelen Reveals Auto-Regulation and High-Temperature Adaption of Probable Two-Speed Genome

Sclerotia of Wolfiporia hoelen are one of the most important traditional Chinese medicines and are commonly used in China, Japan, Korea, and other Asian countries. In the present study, we presented the first high-quality homokaryotic genome of W. hoelen with 14 chromosomes which was evaluated with assembly index, telomere position detection, and whole-genome collinearity. A 64.44 Mb genome was assembled with a Contig N50 length of 3.76 Mb. The imbalanced distribution of transposons and chromosome characters revealed the probable two-speed genome of W. hoelen. High consistency between methylation and transposon conserved the genome stability. The expansion of the gene family about signal transduction and nutritional transport has intimate relationships with sclerotial formation. Up-regulation of expression for distinctive decomposition enzymes, ROS clearance genes, biosynthesis of unsaturated fatty acids, and change of the cell wall components maintained high-speed growth of mycelia that may be the high-temperature adaption strategy of W. hoelen. Further, the analysis of mating-control genes demonstrated that HD3 probably had no function on mating recognition, with the HD protein in a distant genetic with known species. Overall, the high-quality genome of W. hoelen provided crucial information for genome structure and stability, high-temperature adaption, and sexual and asexual process.

Salicylic Acid Enhances Heat Stress Resistance of Pleurotus ostreatus (Jacq.) P. Kumm through Metabolic Rearrangement

Pleurotus ostreatus (Jacq.) P. Kumm is cultivated worldwide, and its growth is seriously threatened by heat stress. Here, we performed a comprehensive analysis to investigate the influence of the phytohormone salicylic acid (SA) in P. ostreatus under HS. The results showed that the hyphal growth recovery rate and the antioxidant capacity of P. ostreatus increased with exogenous SA application (0.01 mmol/L and 0.05 mmol/L) after HS treatment. Metabolomic and transcriptomic analyses showed that SA application (0.05 mmol/L) weakened central carbon metabolism to allow cells to survive HS efficiently. In addition, SA shifted glycolysis to one-carbon metabolism to produce ROS scavengers (GSH and NADPH) and reduced ROS production by altering mitochondrial metabolism. SA also maintained nucleotide homeostasis, led to membrane lipid remodeling, activated the MAPK pathway, and promoted the synthesis of cell-wall components. This study provides a reference for further study of SA in microorganisms.

Spermidine Regulates Mitochondrial Function by Enhancing eIF5A Hypusination and Contributes to Reactive Oxygen Species Production and Ganoderic Acid Biosynthesis in Ganoderma lucidum

Spermidine, a kind of polycation and one important member of the polyamine family, is essential for survival in many kinds of organisms and participates in the regulation of cell growth and metabolism. To explore the mechanism by which spermidine regulates ganoderic acid (GA) biosynthesis in Ganoderma lucidum, the effects of spermidine on GA and reactive oxygen species (ROS) contents were examined. Our data suggested that spermidine promoted the production of mitochondrial ROS and positively regulated GA biosynthesis. Further research revealed that spermidine promoted the translation of mitochondrial complexes I and II and subsequently influenced their activity. With a reduction in eukaryotic translation initiation factor 5A (eIF5A) hypusination by over 50% in spermidine synthase gene (spds) knockdown strains, the activities of mitochondrial complexes I and II were reduced by nearly 60% and 80%, respectively, and the protein contents were reduced by over 50%, suggesting that the effect of spermidine on mitochondrial complexes I and II was mediated through its influence on eIF5A hypusination. Furthermore, after knocking down eIF5A, the deoxyhypusine synthase gene (dhs), and the deoxyhypusine hydroxylase gene (dohh), the mitochondrial ROS level was reduced by nearly 50%, and the GA content was reduced by over 40%, suggesting that eIF5A hypusination contributed to mitochondrial ROS production and GA biosynthesis. In summary, spermidine maintains mitochondrial ROS homeostasis by regulating the translation and subsequent activity of complexes I and II via eIF5A hypusination and promotes GA biosynthesis via mitochondrial ROS signaling. The present findings provide new insight into the spermidine-mediated biosynthesis of secondary metabolites. IMPORTANCE Spermidine is necessary for organism survival and is involved in the regulation of various biological processes. However, the specific mechanisms underlying the various physiological functions of spermidine are poorly understood, especially in microorganisms. In this study, we found that spermidine hypusinates eIF5A to promote the production of mitochondrial ROS and subsequently regulate secondary metabolism in microorganisms. Our study provides a better understanding of the mechanism by which spermidine regulates mitochondrial function and provides new insight into the spermidine-mediated biosynthesis of secondary metabolites.

SNF1β-Modulated Glucose Uptake and the Balance between Polyunsaturated Fatty Acids and Carbohydrates in Mortierella alpina

A sucrose nonfermenting protein kinase 1 (SNF1) complex is an important metabolic regulator in fungi that is critical to cell metabolism and stress response. In this study, the role of an SNF1 β-subunit in the oleaginous fungus Mortierella alpina (MaSip2) was investigated. The MaSip2 contained a glycogen-binding domain and a conserved SNF1-complex interaction region; its transcriptional level during lipogenesis shared high consistency with a previously reported SNF1 γ-subunit (MaSnf4). Overexpression of MaSip2 in M. alpina significantly promoted glucose uptake and resulted in 34.1% increased total biomass, leading to 44.8% increased arachidonic acid yield after 7 day fermentation. MaSip2 also regulated the balance between polyunsaturated fatty acids and carbohydrates in M. alpina. Intracellular metabolite analysis revealed increased carbohydrate-related metabolite accumulation in MaSip2 overexpression strains. On the contrary, knockdown of MaSip2 increased the total fatty acid unsaturation degree, especially under low-temperature conditions. This research improved our knowledge of SNF1 complex in M. alpina and provided a target gene for enhancing glucose utilization and modulating fatty acid composition for better application of oleaginous fungi.

Mitochondrial pyruvate carrier regulates the lignocellulosic decomposition rate through metabolism in Ganoderma lucidum

The activity of mitochondrial pyruvate carrier (MPC) can be modulated to regulate intracellular metabolism under different culture conditions. In Ganoderma lucidum, the role of MPC in regulating carbon sources remains unknown. By knocking down MPC genes (MPC1 and MPC2), this research found that the loss of MPC increased the growth rate of G. lucidum by ~30% in a medium with wood chips as a carbon source. Then cellulase and laccase activities were tested. Endoglucanase and laccase activity increased by ~50% and ~35%, respectively, in MPC knockdown mutants compared with that in the wild type strain. Finally, the expression levels of genes related to glycolysis were assayed, and the transcription levels of these enzymes were found to be increased by ~250% compared with the wild type strain. In conclusion, the regulation of intracellular metabolism by MPC provides a new way to improve the use of nondominant carbon sources such as lignocellulose.

Enhanced multi-stress tolerance and glucose utilization of Saccharomyces cerevisiae by overexpression of the SNF1 gene and varied beta isoform of Snf1 dominates in stresses

Background

The Saccharomyces cerevisiae Snf1 complex is a member of the AMP-activated protein kinase family and plays an important role in response to environmental stress. The α catalytic subunit Snf1 regulates the activity of the protein kinase, while the β regulatory subunits Sip1/Sip2/Gal83 specify substrate preferences and stress response capacities of Snf1. In this study, we aim to investigate the effects of SNF1 overexpression on the cell tolerance and glucose consumption of S. cerevisiae in high glucose, ethanol, and heat stresses and to explore the valid Snf1 form in the light of β subunits in these stresses.

Results

The results suggest that overexpression of SNF1 is effective to improve cell resistance and glucose consumption of S. cerevisiae in high glucose, ethanol, and heat stresses, which might be related to the changed accumulation of fatty acids and amino acids and altered expression levels of genes involved in glucose transport and glycolysis. However, different form of β regulatory subunits dominated in stresses with regard to cell tolerance and glucose utilization. The Sip1 isoform was more necessary to the growth and glucose consumption in ethanol stress. The glucose uptake largely depended on the Sip2 isoform in high sugar and ethanol stresses. The Gal83 isoform only contributed inferior effect on the growth in ethanol stress. Therefore, redundancy and synergistic effect of β subunits might occur in high glucose, ethanol, and heat stresses, but each subunit showed specificity under various stresses.

Conclusions

This study enriches the understanding of the function of Snf1 protein kinase and provides an insight to breed multi-stress tolerant yeast strains.

Effects of different graphene-based nanomaterials as elicitors on growth and ganoderic acid production by Ganoderma lucidum

Graphene-based nanomaterials (GBNs) have attracted considerable interest nowadays due to their wide range of applications. However, very little attention has been paid to the application of nanomaterials as potential elicitors for production of valuable metabolites. Herein, aiming to earn insight into effects of nanomaterials on secondary metabolite biosynthesis by medicinal fungi, we evaluated the influence of GBNs on growth and production of ganoderic acid (GA) by Ganoderma lucidum in submerged culture. Graphene oxide (GO), reduced graphene oxide (rGO), and rGO/Fe₃ O₄ nanocomposite were synthesized successfully and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy analysis. The prepared nanomaterials were added to the culture of G. lucidum at final concentrations of 50, 100, and 150 mg/L on Day 5. The results showed that the elicitation of G. lucidum with GO and rGO decreased the cell dry weight and GA production slightly, especially in higher concentrations. However, rGO/Fe₃ O₄ nanocomposite not negatively affected cell growth and improved GA production. G. lucidum growth rate responded to elicitation experiments differently and depended on the type of nanomaterials and their concentrations, but almost all GBNs caused an increase in GA content (mg/100 mg dry weight). Also, field emission scanning electron microscopy morphological study showed that under elicitation, mycelia were more condensed and tightly stacked together. The findings from this study may suggest that GBNs in low concentrations could be applied as elicitors to secondary metabolites production from higher fungus, but further environmental, physiological, and biological studies required.