Molecular cloning, characterization, and function analysis of a mevalonate pyrophosphate decarboxylase gene from Ganoderma lucidum

Current Advances in the Functional Genes of Edible and Medicinal Fungi: Research Techniques, Functional Analysis, and Prospects

Functional genes encode various biological functions required for the life activities of organisms. By analyzing the functional genes of edible and medicinal fungi, varieties of edible and medicinal fungi can be improved to enhance their agronomic traits, growth rates, and ability to withstand adversity, thereby increasing yield and quality and promoting industrial development. With the rapid development of functional gene research technology and the publication of many whole-genome sequences of edible and medicinal fungi, genes related to important biological traits have been mined, located, and functionally analyzed. This paper summarizes the advantages and disadvantages of different functional gene research techniques and application examples for edible and medicinal fungi; systematically reviews the research progress of functional genes of edible and medicinal fungi in biological processes such as mating type, mycelium and fruit growth and development, substrate utilization and nutrient transport, environmental response, and the synthesis and regulation of important active substances; and proposes future research directions for functional gene research for edible and medicinal fungi. The overall aim of this study was to provide a valuable reference for further promoting the molecular breeding of edible and medicinal fungi with high yield and quality and to promote the wide application of edible and medicinal fungi products in food, medicine, and industry.

Combined NMR and MS-based metabonomics and real-time PCR analyses reveal dynamic metabolic changes of Ganoderma lucidum during fruiting body growing

Ganoderma lucidum (G. lucidum) is a rare medicinal fungus with various beneficial properties. One of its main components, ganoderic acids (GAs), are important triterpenoids known for their sedative and analgesic, hepatoprotective, and anti-tumor activities. Understanding the growth and development of the G. lucidum fruiting body is crucial for determining the optimal time to harvest them. In this study, we used nuclear magnetic resonance (NMR) spectroscopy to systematically characterize the metabolites of G. lucidum at seven distinct developmental stages. We also measured the contents of seven kinds of GAs using LC-MS/MS. A total of 49 metabolites were detected in G. lucidum, including amino acids, sugars, organic acids and GAs. During the transition from the bud development period (I) to the budding period (II), we observed a rapid accumulation of glucose, tyrosine, nicotinamide ribotide, inosine and GAs. After the budding period, the contents of most metabolites decreased until the mature period (VII). In addition, the contents of GAs showed an initial raising, followed by a decline during the elongation period, except for GAF, which exhibited a rapid raise during the mature stage. We also detected the expression of several genes involved in GA synthesis, finding that most genes including 16 cytochrome P450 monooxygenase were all down-regulated during periods IV and VII compared to period I. These findings provide valuable insights into the dynamic metabolic profiles of G. lucidum throughout its growth stage, and it is recommended to harvest G. lucidum at period IV.

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.

Development of a Transformation System for the Medicinal Fungus Sanghuangporus baumii and Acquisition of High-Value Strain

To further explore the molecular mechanism of triterpenoid biosynthesis and acquire high-value strain of Sanghuangporus baumii, the Agrobacterium tumefaciens-mediated transformation (ATMT) system was studied. The key triterpenoid biosynthesis-associated gene isopentenyl diphosphate isomerase (IDI) was transformed into S. baumii by ATMT system. Then, the qRT-PCR technique was used to analyze gene transcript level, and the widely targeted metabolomics was used to investigate individual triterpenoid content. Total triterpenoid content and anti-oxidant activity were determined by spectrophotometer. In this study, we for the first time established an efficient ATMT system and transferred the IDI gene into S. baumii. Relative to the wild-type (WT) strain, the IDI-transformant (IT) strain showed significantly higher transcript levels of IDI and total triterpenoid content. We then investigated individual triterpenoids in S. baumii, which led to the identification of 10 distinct triterpenoids. The contents of individual triterpenoids produced by the IT2 strain were 1.76-10.03 times higher than those produced by the WT strain. The triterpenoid production showed a significant positive correlation with the IDI gene expression. Besides, IT2 strain showed better anti-oxidant activity. The findings provide valuable information about the biosynthetic pathway of triterpenoids and provide a strategy for cultivating high-value S. baumii strains.

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.

A Review of Ganoderma Triterpenoids and Their Bioactivities

For centuries, Ganoderma has been used as a traditional medicine in Asian countries to prevent and treat various diseases. Numerous publications are stating that Ganoderma species have a variety of beneficial medicinal properties, and investigations on different metabolic regulations of Ganoderma species, extracts or isolated compounds have been performed both in vitro and in vivo. However, it has frequently been questioned whether Ganoderma is simply a dietary supplement for health or just a useful "medication" for restorative purposes. More than 600 chemical compounds including alkaloids, meroterpenoids, nucleobases, nucleosides, polysaccharides, proteins, steroids and triterpenes were extracted and identified from Ganoderma, with triterpenes serving as the primary components. In recent years, Ganoderma triterpenes and other small molecular constituents have aroused the interest of chemists and pharmacologists. Meanwhile, considering the significance of the triterpene constituents in the development of new drugs, this review describes 495 compounds from 25 Ganoderma species published between 1984 and 2022, commenting on their source, biosynthetic pathway, identification, biological activities and biosynthesis, together with applications of advanced analytical techniques to the characterization of Ganoderma triterpenoids.

Integrative analysis of the roles of lncRNAs and mRNAs in ischaemic preconditioning to alleviate liver ischaemia-reperfusion injury in mice

The objective of our study was to elucidate the possible underlying mechanism for the protective effect of ischaemic preconditioning (IPC) against ischaemia-reperfusion (I/R) injury and to provide new research perspectives of long non-coding RNAs (lncRNAs). In this study, serum and liver tissue samples were collected to measure indexes of liver injury from a mouse liver model in sham, I/R injury and I/R + IPC groups. Furthermore, liver samples from 5 randomly selected mice per group were extracted and subjected to the microarray and subsequent bioinformatics analysis. IPC ameliorated liver damage by lowered liver transaminase levels and pro-inflammatory cytokines. A total of 167 lncRNAs and 108 messenger RNAs (mRNAs) were significantly differentially expressed genes (DEGs) between the I/R + IPC and I/R groups. Gene Ontology (GO) analysis revealed that these genes were mainly related to unfolded proteins, responses to topologically incorrect proteins, responses to temperature stimuli, protein folding and protein refolding. Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway analysis indicated that the DEGs were enriched in the following pathways: protein processing in the endoplasmic reticulum; antigen processing and presentation; and fructose and mannose metabolism. Additionally, the 7 selected DEGs (Hspa1ab, Chka, Clec2h, Mvd, Adra1a, AK085737 and AK088966) were validated in modules of the lncRNA-mRNA weighted coexpression network, which agreed with the qRT-PCR and chip data. And the identified differentially expressed lncRNAs and mRNAs may provide new clues to understand the pivotal pathophysiological mechanism by which IPC alleviates I/R-caused liver damage.

Comparative transcriptome analysis of genes and metabolic pathways involved in sporulation in Ganoderma lingzhi

Over the past decades, Ganoderma lingzhi spores have received considerable attention as a great potential pharmaceutical resource. However, the genetic regulation of sporulation is not well understood. In this study, a comparative transcriptome analysis of the low-sporing HZ203 and high-sporing YW-1 was performed to characterize the mechanism underlying sporulation. A total of 917 differentially expressed genes were identified in HZ203 and 1,450 differentially expressed genes in YW-1. Differentially expressed genes involved in sporulation were identified, which included HOP1, Mek1, MSH4, MSH5, and Spo5 in meiosis. Positive regulatory pathways of sporulation were proposed as 2 transcriptional factors had high connectivity with MSH4 and Spo5. Furthermore, we found that the pathways associated with energy production were enriched in the high-sporing genotype, such as the glyoxylate and dicarboxylate metabolism, starch and sucrose metabolism. Finally, we performed a weighted gene coexpression network analysis and found that the hub genes of the module which exhibit strong positive relationship with the high-sporing phase purportedly participate in signal transduction, carbohydrate transport and metabolism. The dissection of differentially expressed genes during sporulation extends our knowledge about the genetic and molecular networks mediating spore morphogenesis and sheds light on the importance of energy source during sporulation.

Biosynthesis and regulation of terpenoids from basidiomycetes: exploration of new research

Basidiomycetes, also known as club fungi, consist of a specific group of fungi. Basidiomycetes produce a large number of secondary metabolites, of which sesquiterpenoids, diterpenoids and triterpenoids are the primary components. However, these terpenoids tend to be present in low amounts, which makes it difficult to meet application requirements. Terpenoid biosynthesis improves the quantity of these secondary metabolites. However, current understanding of the biosynthetic mechanism of terpenoids in basidiomycetes is insufficient. Therefore, this article reviews the latest research on the biosynthesis of terpenoids in basidiomycetes and summarizes the CYP450 involved in the biosynthesis of terpenoids in basidiomycetes. We also propose opportunities and challenges for chassis microbial heterologous production of terpenoids in basidiomycetes and provide a reference basis for the better development of basidiomycete engineering.

In silico/computational analysis of mevalonate pyrophosphate decarboxylase gene families in Campanulids

Mevalonate pyrophosphate decarboxylase (MPD) is a key enzyme in terpenoid biosynthesis. MPD plays an important role in the upstream regulation of secondary plant metabolism. However, studies on the MPD gene are relatively very few despite its importance in plant metabolism. Currently, no systematic analysis has been conducted on the MPD gene in plants under the order Apiales, which comprises important medicinal plants such as Panax ginseng and Panax notoginseng. This study sought to explore the structural characteristics of the MPD gene and the effect of adaptive evolution on the gene by comparing and analyzing MPD gene sequences of different campanulids species. For that, phylogenetic and adaptive evolution analyses were carried out using sequences for 11 Campanulids species. MPD sequence characteristics of each species were then analyzed, and the collinearity analysis of the genes was performed. As a result, a total of 21 MPD proteins were identified in 11 Campanulids species through BLAST analysis. Phylogenetic analysis, physical and chemical properties prediction, gene family analysis, and gene structure prediction showed that the MPD gene has undergone purifying selection and exhibited highly conserved structure. Analysis of physicochemical properties further showed that the MPD protein was a hydrophilic protein without a transmembrane region. Moreover, collinearity analysis in Apiales showed that MPD gene on chromosome 2 of D. carota and chromosome 1 of C. sativum were collinear. The findings showed that MPD gene is highly conserved. This may be a common characteristic of all essential enzymes in the biosynthesis pathways of medicinal plants. Notably, MPD gene is significantly affected by environmental factors which subsequently modulate its expression. The current study’s findings provide a basis for follow-up studies on MPD gene and key enzymes in other medicinal plants.

Integrative Analysis of Selected Metabolites and the Fungal Transcriptome during the Developmental Cycle of Ganoderma lucidum Strain G0119 Correlates Lignocellulose Degradation with Carbohydrate and Triterpenoid Metabolism

To systemically understand the biosynthetic pathways of bioactive substances, including triterpenoids and polysaccharides, in Ganoderma lucidum, the correlation between substrate degradation and carbohydrate and triterpenoid metabolism during growth was analyzed by combining changes in metabolite content and changes in related enzyme expression in G. lucidum over 5 growth phases. Changes in low-polarity triterpenoid content were correlated with changes in glucose and mannitol contents in fruiting bodies. Additionally, changes in medium-polarity triterpenoid content were correlated with changes in the lignocellulose content of the substrate and with the glucose, trehalose, and mannitol contents of fruiting bodies. Weighted gene coexpression network analysis (WGCNA) indicated that changes in trehalose and polyol contents were related to carbohydrate catabolism and polysaccharide synthesis. Changes in triterpenoid content were related to expression of the carbohydrate catabolic enzymes laccase, cellulase, hemicellulase, and polysaccharide synthase and to the expression of several cytochrome P450 monooxygenases (CYPs). It was concluded that the products of cellulose and hemicellulose degradation participate in polyol, trehalose, and polysaccharide synthesis during initial fruiting body formation. These carbohydrates accumulate in the early phase of fruiting body formation and are utilized when the fruiting bodies mature and a large number of spores are ejected. An increase in carbohydrate metabolism provides additional precursors for the synthesis of triterpenoids. IMPORTANCE Most studies of G. lucidum have focused on its medicinal function and on the mechanism of its activity, whereas the physiological metabolism and synthesis of bioactive substances during the growth of this species have been less studied. Therefore, theoretical guidance for cultivation methods to increase the production of bioactive compounds remains lacking. This study integrated changes in the lignocellulose, carbohydrate, and triterpenoid contents of G. lucidum with enzyme expression from transcriptomics data using WGCNA. The findings helped us better understand the connections between substrate utilization and the synthesis of polysaccharides and triterpenoids during the cultivation cycle of G. lucidum. The results of WGCNA suggest that the synthesis of triterpenoids can be enhanced not only through regulating the expression of enzymes in the triterpenoid pathway, but also through regulating carbohydrate metabolism and substrate degradation. This study provides a potential approach and identifies enzymes that can be targeted to regulate lignocellulose degradation and accelerate the accumulation of bioactive substances by regulating substrate degradation in G. lucidum.

Transcriptome dynamics and metabolite analysis revealed the candidate genes and regulatory mechanism of ganoderic acid biosynthesis during liquid superficial-static culture of Ganoderma lucidum

Ganoderic acid (GA), an important secondary metabolite of Ganoderma lucidum, exhibited many significant pharmacological activities. In this study, the biosynthetic mechanism of GAs was investigated by comparing metabolites and transcriptome dynamics during liquid superficial‐static culture (LSSC) and submerged culture (SC). LSSC was a better method to produce GA because thirteen GAs were identified from mycelia by UPLC‐QTOF‐MS, and the content of all GAs was higher in LSSC than in SC. Ergosterol was accumulated during the SC process in G. lucidum. Transcriptome dynamics analysis revealed CYP5150L8 was the key gene regulating lanosterol flux into GA biosynthesis. Other sixteen CYP450 genes were significantly higher expressed during the culture time in LSSC and could be potential candidate genes associated with the biosynthesis of different GAs. In addition, six of the ten expressed genes in ergosterol biosynthetic pathway shown upregulated at some time points in SC. These results not only provide a fundamental information of the key genes in ergosterol and GA biosynthetic pathway, but also provide directions for future elucidating the regulatory mechanisms of GAs in G. lucidum and enabling us to promote the development and utilization of LSSC at the industrial level.

Function of ceramide synthases on growth, ganoderic acid biosynthesis and sphingolipid homeostasis in Ganoderma lucidum

Ceramide synthases (CERSs) catalyse an N-acyltransferase reaction using long-chain base (LCB) and fatty acyl-coenzyme A (CoA) as substrates to synthesize ceramide (Cer), which is the backbone of all complex sphingolipids. In the present study, three CERSs (LAG1, LAG2 and LAG3) form Ganoderma lucidum were analysed. The silencing of lag1 by RNA interference reduced ganoderic acid biosynthesis and Cer and complex sphingolipids contents, which contain long-chain-fatty-acids (LCFAs, including C16 and C18). In contrast, the silencing of lag2 or lag3 did not result in obvious phenotypic and sphingolipid homeostasis changes, although the lag2/lag3 double-silenced mutants exhibited increased ganoderic acid biosynthesis as well as reduced growth, reduced Cer and complex sphingolipids contents, which contain very-long-chain fatty acids (VLCFAs, including C22, C24 and C26). The results of the present study indicate that the three assayed CERSs have distinct physiological functions and substrate specificities in G. lucidum.

Mevalonate Diphosphate Decarboxylase MVD/Erg19 Is Required for Ergosterol Biosynthesis, Growth, Sporulation and Stress Tolerance in Aspergillus oryzae

Mevalonate diphosphate decarboxylase (MVD; EC 4.1.1.33) is a key enzyme of the mevalonic acid (MVA) pathway. In fungi, the MVA pathway functions as upstream of ergosterol biosynthesis, and MVD is also known as Erg19. Previously, we have identified Aoerg19 in Aspergillus oryzae using bioinformatic analysis. In this study, we showed that AoErg19 function is conserved using phylogenetic analysis and yeast complementation assay. Quantitative reverse transcription-PCR (qRT-PCR) indicated that Aoerg19 expression changed in different growth stages and under different forms of abiotic stress. Subcellular localization analysis showed that AoErg19 was located in the vacuole. Overexpression of Aoerg19 decreased the ergosterol content in A. oryzae, which may due to the feedback-mediated downregulation of Aoerg8. Consistent with the decrease in ergosterol content, both Aoerg19 overexpression and RNAi strains of A. oryzae are sensitive to abiotic stressors, including ergosterol biosynthesis inhibitor, temperature, salt and ethanol. Thus, we have identified the function of AoErg19 in A. oryzae, which may assist in genetic modification of MVA and the ergosterol biosynthesis pathway.

Shedding light on the mechanisms underlying the environmental regulation of secondary metabolite ganoderic acid in Ganoderma lucidum using physiological and genetic methods

The secondary metabolites of fungi are often produced at very low concentrations, and until recently the regulatory mechanisms of secondary metabolite biosynthesis have been unclear. Ganoderma lucidum is a macrofungus that is widely used as a traditional Chinese medicine or medicinal mushroom: ganoderic acid (GA) is one of the main active ingredients. Here, we review research from the last decade on which and how environmental factors regulate GA biosynthesis. These environmental factors are mainly three components: a single chemical/biological or biochemical signal, physical triggers, and nutritional conditions. Because G. lucidum is a non-model Basidiomycete, a combination of physiological and genetic research is needed to determine how those environmental factors regulate GA biosynthesis. The regulation of GA biosynthesis includes ROS, Ca²⁺, cAMP and phospholipid signaling, and cross-talk between different signaling pathways. The regulatory mechanisms for the synthesis of this secondary metabolite, from the perspective of physiology and genetics, in G. lucidum will provide ideas for studying the regulation of fungal secondary metabolism in other non-model species, especially those fungi with limitations in genetic manipulation.

Metabolism of ganoderic acids by a Ganoderma lucidum cytochrome P450 and the 3-keto sterol reductase ERG27 from yeast

Ganoderic acids, a group of oxygenated lanostane-type triterpenoids, are the major bioactive compounds produced by the well-known medicinal macro fungus Ganoderma lucidum. More than 150 ganoderic acids have been identified, and the genome of G. lucidum has been sequenced recently. However, the biosynthetic pathways of ganoderic acids have not yet been elucidated. Here, we report the functional characterization of a cytochrome P450 gene CYP512U6 from G. lucidum, which is involved in the ganoderic acid biosynthesis. CYP512U6 hydroxylates the ganoderic acids DM and TR at the C-23 position to produce hainanic acid A and ganoderic acid Jc, respectively. In addition, CYP512U6 can also hydroxylate a modified ganoderic acid DM in which the C-3 ketone has been reduced to hydroxyl by the sterol reductase ERG27 from Saccharomyces cerevisiae. An NADPH-dependent cytochrome P450 reductase from G. lucidum was also isolated and characterized. These results will help elucidate the biosynthetic pathways of ganoderic acids.

Cross Talk between Calcium and Reactive Oxygen Species Regulates Hyphal Branching and Ganoderic Acid Biosynthesis in Ganoderma lucidum under Copper Stress

Ganoderma lucidum is among the best known medicinal basidiomycetes due to its production of many pharmacologically active compounds. To study the regulatory networks involved in its growth and development, we analyzed the relationship between reactive oxygen species (ROS) and Ca²⁺ signaling in the regulation of hyphal branching and ganoderic acid (GA) biosynthesis after Cu²⁺ treatment. Our results revealed that Cu²⁺ treatment decreased the distance between hyphal branches and increased the GA content and the intracellular levels of ROS and Ca²⁺ Further research revealed that the Cu²⁺-induced changes in hyphal branch distance, GA content, and cytosolic Ca²⁺ level were dependent on increases in cytosolic ROS. Our results also showed that increased cytosolic Ca²⁺ could reduce cytosolic ROS by activating antioxidases and modulating Cu²⁺ accumulation, resulting in feedback to adjust hyphal growth and GA biosynthesis. These results indicated that cytosolic ROS and Ca²⁺ levels exert important cross talk in the regulation of hyphal growth and GA biosynthesis induced by Cu²⁺ Taken together, our results provide a reference for analyzing the interactions among different signal transduction pathways with regard to the regulation of growth and development in other filamentous fungi.IMPORTANCEGanoderma lucidum, which is known as an important medicinal basidiomycete, is gradually becoming a model organism for studying environmental regulation and metabolism. In this study, we analyzed the relationship between reactive oxygen species (ROS) and Ca²⁺ signaling in the regulation of hyphal branching and ganoderic acid (GA) biosynthesis under Cu²⁺ stress. The results revealed that the Cu²⁺-induced changes in the hyphal branch distance, GA content, and cytosolic Ca²⁺ level were dependent on increases in cytosolic ROS. Furthermore, the results indicated that increased cytosolic Ca²⁺ could reduce cytosolic ROS levels by activating antioxidases and modulating Cu²⁺ accumulation. The results in this paper indicate that there was important cross talk between cytosolic ROS and Ca²⁺ levels in the regulation of hyphal growth and GA biosynthesis induced by Cu².

Conversion of phosphatidylinositol (PI) to PI4-phosphate (PI4P) and then to PI(4,5)P2 is essential for the cytosolic Ca2+ concentration under heat stress in Ganoderma lucidum

How cells drive the phospholipid signal response to heat stress (HS) to maintain cellular homeostasis is a fundamental issue in biology, but the regulatory mechanism of this fundamental process is unclear. Previous quantitative analyses of lipids showed that phosphatidylinositol (PI) accumulates after HS in Ganoderma lucidum, implying the inositol phospholipid signal may be associated with HS signal transduction. Here, we found that the PI-4-kinase and PI-4-phosphate-5-kinase activities are activated and that their lipid products PI-4-phosphate and PI-4,5-bisphosphate are increased under HS. Further experimental results showed that the cytosolic Ca²⁺ ([Ca²⁺ ]_c ) and ganoderic acid (GA) contents induced by HS were decreased when cells were pretreated with Li⁺ , an inhibitor of inositol monophosphatase, and this decrease could be rescued by PI and PI-4-phosphate. Furthermore, inhibition of PI-4-kinases resulted in a decrease in the Ca²⁺ and GA contents under HS that could be rescued by PI-4-phosphate but not PI. However, the decrease in the Ca²⁺ and GA contents by silencing of PI-4-phosphate-5-kinase could not be rescued by PI-4-phosphate. Taken together, our study reveals the essential role of the step converting PI to PI-4-phosphate and then to PI-4,5-bisphosphate in [Ca²⁺ ]_c signalling and GA biosynthesis under HS.

Phospholipase D and phosphatidic acid mediate heat stress induced secondary metabolism in Ganoderma lucidum

Phospholipid-mediated signal transduction plays a key role in responses to environmental changes, but little is known about the role of phospholipid signalling in microorganisms. Heat stress (HS) is one of the most important environmental factors. Our previous study found that HS could induce the biosynthesis of the secondary metabolites, ganoderic acids (GA). Here, we performed a comprehensive mass spectrometry-based analysis to investigate HS-induced lipid remodelling in Ganoderma lucidum. In particular, we observed a significant accumulation of phosphatidic acid (PA) on HS. Further genetic tests in which pld-silencing strains were constructed demonstrated that the accumulation of PA is dependent on HS-activated phospholipase D (PLD) hydrolysing phosphatidylethanolamine. Furthermore, we determined the role of PLD and PA in HS-induced secondary metabolism in G. lucidum. Exogenous 1-butanol, which decreased PLD-mediated formation of PA, reverses the increased GA biosynthesis that was elicited by HS. The pld-silenced strains partly blocked HS-induced GA biosynthesis, and this block can be reversed by adding PA. Taken together, our results suggest that PLD and PA are involved in the regulation of HS-induced secondary metabolism in G. lucidum. Our findings provide key insights into how microorganisms respond to heat stress and then consequently accumulate secondary metabolites by phospholipid remodelling.

Heat Stress Modulates Mycelium Growth, Heat Shock Protein Expression, Ganoderic Acid Biosynthesis, and Hyphal Branching of Ganoderma lucidum via Cytosolic Ca2

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.

IMPORTANCE

Ganoderma 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.

Bioinformatics analysis of hepatitis C virus genotype 2a-induced human hepatocellular carcinoma in Huh7 cells

Hepatocellular carcinoma (HCC) is a liver cancer that could be induced by hepatitis C virus genotype 2a Japanese fulminant hepatitis-1 (JFH-1) strain. The aim of this study was to investigate the molecular mechanisms of HCC. The microarray data GSE20948 includes 14 JFH-1- and 14 mock (equal volume of medium [control])-infected Huh7 samples. The data were downloaded from the Gene Expression Omnibus. After data processing, soft cluster analyses were performed to identify co-regulated genes with similar temporal expression patterns. Functional and pathway enrichment analyses, as well as functional annotation analysis, were performed. Subsequently, combined networks of protein–protein interaction network, microRNA regulatory network, and transcriptional regulatory network were constructed. Hub nodes, modules, and five clusters of co-regulated genes were also identified. In total, 173 up and 207 down co-regulated genes were separately identified in JFH-1-infected Huh7 cells compared with those of control cells. Functional enrichment analysis indicated that up co-regulated genes were related to skeletal system morphogenesis and neuron differentiation and down co-regulated genes were related to steroid/cholesterol/sterol metabolisms. Hub genes (such as IRF1, GBP1, ICAM1, Foxa1, DHCR7, HMGCS2, and MSMO1) were identified. Transcription factors IRF1 and Foxa1 were the targets of miR-130a, miR-17-5p, and miR-20a. PPARGC1A was targeted by miR-29 family, and MSMO1 was the target of miR-23 family. Hub nodes (such as IRF1, GBP1, ICAM1, Foxa1, DHCR7, HMGCS2, and MSMO1) and microRNAs might be used as candidate biomarkers of JFH-1-infected HCC.

UDP-glucose pyrophosphorylase influences polysaccharide synthesis, cell wall components, and hyphal branching in Ganoderma lucidum via regulation of the balance between glucose-1-phosphate and UDP-glucose

UDP-glucose pyrophosphorylase (UGP) is a key enzyme involved in carbohydrate metabolism, but there are few studies on the functions of this enzyme in fungi. The ugp gene of Ganoderma lucidum was cloned, and enzyme kinetic parameters of the UGP recombinant protein were determined in vitro, revealing that this protein was functional and catalyzed the reversible conversion between Glc-1-P and UDP-Glc. ugp silencing by RNA interference resulted in changes in the levels of the intermediate metabolites Glc-1-P and UDP-Glc. The compounds and structure of the cell wall in the silenced strains were also altered compared with those in the wild-type strains. Moreover, the number of hyphal branches was also changed in the silenced strains. To verify the role of UGP in hyphal branching, a ugp-overexpressing strain was constructed. The results showed that the number of hyphal branches was influenced by UGP. The mechanism underlying hyphal branching was further investigated by adding exogenous Glc-1-P. Our results showed that hyphal branching was regulated by a change in the cytosolic Ca(2+) concentration, which was affected by the level of the intermediate metabolite Glc-1-P, in G. lucidum. Our findings indicate the existence of an interaction between carbon metabolism and Ca(2+) signaling in this fungus.

Profiling and quantifying differential gene transcription provide insights into ganoderic acid biosynthesis in Ganoderma lucidum in response to methyl jasmonate

Ganoderma lucidum is a mushroom with traditional medicinal properties that has been widely used in China and other countries in Eastern Asia. Ganoderic acids (GA) produced by G. lucidum exhibit important pharmacological activities. Previous studies have demonstrated that methyl jasmonate (MeJA) is a potent inducer of GA biosynthesis and the expression of genes involved in the GA biosynthesis pathway in G. lucidum. To further explore the mechanism of GA biosynthesis, cDNA-Amplified Fragment Length Polymorphism (cDNA-AFLP) was used to identify genes that are differentially expressed in response to MeJA. Using 64 primer combinations, over 3910 transcriptionally derived fragments (TDFs) were obtained. Reliable sequence data were obtained for 390 of 458 selected TDFs. Ninety of these TDFs were annotated with known functions through BLASTX searching the GenBank database, and 12 annotated TDFs were assigned into secondary metabolic pathways by searching the KEGGPATHWAY database. Twenty-five TDFs were selected for qRT-PCR analysis to confirm the expression patterns observed with cDNA-AFLP. The qRT-PCR results were consistent with the altered patterns of gene expression revealed by the cDNA-AFLP technique. Additionally, the transcript levels of 10 genes were measured at the mycelium, primordia, and fruiting body developmental stages of G. lucidum. The greatest expression levels were reached during primordia for all of the genes except cytochrome b2 reached its highest expression level in the mycelium stage. This study not only identifies new candidate genes involved in the regulation of GA biosynthesis but also provides further insight into MeJA-induced gene expression and secondary metabolic response in G. lucidum.

The development and application of a multiple gene co-silencing system using endogenous URA3 as a reporter gene in Ganoderma lucidum

Ganoderma lucidum is one of the most important medicinal mushrooms; however, molecular genetics research on this species has been limited due to a lack of reliable reverse genetic tools. In this study, the endogenous orotidine 5′-monophosphate decarboxylase gene (URA3) was cloned as a silencing reporter, and four gene-silencing methods using hairpin, sense, antisense, and dual promoter constructs, were introduced into G. lucidum through a simple electroporation procedure. A comparison and evaluation of silencing efficiency demonstrated that all of the four methods differentially suppressed the expression of URA3. Our data unequivocally indicate that the dual promoter silencing vector yields the highest rate of URA3 silencing compared with other vectors (up to 81.9%). To highlight the advantages of the dual promoter system, we constructed a co-silencing system based on the dual promoter method and succeeded in co-silencing URA3 and laccase in G. lucidum. The reduction of the mRNA levels of the two genes were correlated. Thus, the screening efficiency for RNAi knockdown of multiple genes may be improved by the co-silencing of an endogenous reporter gene. The molecular tools developed in this study should facilitate the isolation of genes and the characterization of the functions of multiple genes in this pharmaceutically important species, and these tools should be highly useful for the study of other basidiomycetes.