Nox gene expression and cytochemical localization of hydrogen peroxide in Polyporus umbellatus sclerotial formation

Functional characterization of a catalase gene PtCat associated with sclerotia formation in Pleurotus tuber-regium

Pleurotus tuber-regium (Fr.) Sing. can evade oxygen by forming sclerotia under oxidative stress, consequently averting the development of hyperoxidative state, during which the expression level of catalase gene (PtCat) is significantly up-regulated. To investigate the relationship between the catalase gene and sclerotia formation, over-expression and interference strains of the PtCat gene were obtained by Agrobacterium tumefaciens-mediated transformation for phenotypic analysis. In the absence of hydrogen peroxide (H2O2) stress, a minor difference was observed in the mycelial growth rate and the activity of antioxidant enzymes between the over-expression and interference strains. However, when exposed to 1-2 mM H2O2, the colony diameter of the over-expression strain was approximately 2-3× that of the interference strain after 8 days of culturing. The catalase activity of the over-expression strain increased by 1000 U/g under 2 mM H2O2 stress, while the interference strain increased by only 250 U/g. After one month of cultivation, the interference strain formed an oval sclerotium measuring 3.5 cm on the long axis and 2 cm on the short axis, while the over-expression strain did not form sclerotia. Therefore, it is concluded that catalase activity regulates the formation of sclerotia in P. tuber-regium.

Relationship between antioxidant enzymes and sclerotial formation of Pleurotus tuber-regium under abiotic stress

In order to explore the relationship between sclerotial formation and antioxidant enzymes under abiotic stresses, the effects of abiotic stresses including temperature, pH value, osmotic pressure, limited nitrogen, and hydrogen peroxide (H₂O₂) on the activities of antioxidant enzymes, ascorbate peroxidase (APX), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in Pleurotus tuber-regium were studied. Meanwhile, the sclerotial formation under these abiotic stress conditions was also investigated. It was found that low temperature, weak alkaline, appropriate osmotic stress, and H₂O₂ can promote sclerotial formation, and sclerotial formation always tended to occur when the activities of antioxidant enzymes were at a high value. During the prolonged low temperature stress, SOD acted mainly in the early stage of stress, while POD and CAT had higher activity in the middle and late stage. Moreover, the reverse transcription quantitative polymerase chain reaction (RT-qPCR) results showed that SOD.193 and POD.535 were significantly down-regulated in sclerotia, and CAT.1115 and POD.401 were up-regulated instead. These antioxidant enzyme genes played an important role in the sclerotial formation under low temperature stress. It is strongly suggested that antioxidant enzymes and abiotic stresses are closely related to sclerotial formation in P. tuber-regium. KEY POINTS: • Low temperature and H2O2 can promote sclerotial formation. • Sclerotia are more likely to form under high antioxidant enzyme activity. • POD.401, POD.535, SOD.193, and CAT.1115 are important for sclerotial formation.

Acetylome analysis of acetylation providing new insight into sclerotial generation in medicinal fungus Polyporus umbellatus

Sclerotium-forming fungi are ecologically diverse and possess notable pathogenic or medicinal properties. The sclerotial generation mechanism is still elusive though Polyporus umbellatus sclerotia are typical Traditional Chinese Medicine with diuretic and antitumor effects. Protein acetylation displays a crucial role in several biological processes, but the functions of acetylation in this valuable fungus are unknown at present. In this study, acetylome of P. umbellatus was studied using nano LC-Triple TOF mass spectrometry system following immune-affinity-based enrichment. Totally, 648 acetylated sites in 342 proteins were identified and nine motifs were found to be conserved in P. umbellatus including K^acY, K^acA, K^acL, K^acG, M^acS, M^acA, R^acA, R^acL, and R^acG. Acetylated proteins taken part in types of biological processes, particularly to those in biological processes associated with reactive oxygen species (ROS) metabolism. Inhibitors complement tests were carried out to verify the role of ROS in acetylation modification. It was concluded that oxidative stress regulated sclerotial generation via proteins acetylation in P. umbellatus. The present study presents new insight into the essential roles of acetylation in sclerotial formation, which may also be applicable for other sclerotium-forming fungi.

Armillaria mellea Symbiosis Drives Metabolomic and Transcriptomic Changes in Polyporus umbellatus Sclerotia

Sclerotia, the medicinal part of Polyporus umbellatus, play important roles in diuresis and renal protection, with steroids and polysaccharides as the main active ingredients. The sclerotia grow and develop only after symbiosis with Armillaria sp. In this study, a systematic metabolomics based on non-targeted UPLC-MS method was carried out between the infected part of the separated cavity wall of the sclerotia (QR) and the uninfected part (the control group, CK) to find and identify differential metabolites. The biosynthetic pathway of characteristic steroids in sclerotia of P. umbellatus was deduced and the content of ergosterol, polyporusterone A and B in the QR and CK groups were detected with the High Performance Liquid Chromatography (HPLC). Furthermore, the expression patterns of putative genes associated with steroid biosynthesis pathway were also performed with quantitative real-time PCR. The results showed that a total of 258 metabolites originated from fungi with the fragmentation score more than 45 and high resolution mass were identified, based on UPLC-MS metabolomic analysis, and there were 118 differentially expressed metabolites (DEMs) between both groups. The metabolic pathways indicated that steroids, fatty acid and carbohydrate were active and enriched during P. umbellatus sclerotia infected by A. mellea. The content of ergosterol, polyporusterone A and B in the QR group increased by 32.2, 75.0, and 20.0%, in comparison to that of the control group. The qRT-PCR analysis showed that series of enzymes including C-8 sterol isomerase (ERG2), sterol C-24 methyltransferase (ERG6) and sterol 22-desaturase (ERG5), which played important roles in the final steps of ergosterol biosynthesis, all presented up-regulated patterns in the QR group in P. umbellatus. The comprehensive metabolomic and transcriptomic information will contribute to further study concerning the mechanisms of P. umbellatus sclerotial formation infected by A. mellea in the future.

Genome and Comparative Transcriptome Dissection Provide Insights Into Molecular Mechanisms of Sclerotium Formation in Culinary-Medicinal Mushroom Pleurotus tuber-regium

Pleurotus tuber-regium is an edible and medicinal sclerotium-producing mushroom. The sclerotia of this mushroom also serve as food and folk medicine. Based on the description of its monokaryon genome, sequenced with Illumina and PacBio sequencing technologies, comparative transcriptomic analysis using RNA sequencing (RNA-seq) was employed to study its mechanism of sclerotium formation. The de novo assembled genome is 35.82 Mb in size with a N50 scaffold size of 4.29 Mb and encodes 12,173 putative proteins. Expression analysis demonstrated that 1,146 and 1,249 genes were upregulated and downregulated with the formation of sclerotia, respectively. The differentially expressed genes were associated with substrate decomposition, the oxidation-reduction process, cell wall synthesis, and other biological processes in P. tuber-regium. These genomic and transcriptomic resources provide useful information for the mechanism underlying sclerotium formation in P. tuber-regium.

Use of transcriptomic profiling to identify candidate genes involved in Polyporus umbellatus sclerotial formation affected by oxalic acid

Polyporus umbellatus is a precious medicinal fungus. Oxalic acid was observed to affect sclerotial formation and sclerotia possessed more medicinal compounds than mycelia. In this study, the transcriptome of P. umbellatus was analysed after the fungus was exposed to various concentrations of oxalic acid. The differentially expressed genes (DEGs) encoding a series of oxidases were upregulated, and reductases were downregulated, in the low-oxalic-acid (Low OA) group compared to the control (No OA) group, while the opposite phenomenon was observed in the high-oxalic-acid (High OA) group. The detection of reactive oxygen species (ROS) in P. umbellatus mycelia was performed visually, and Ca²⁺ and H₂O₂ fluxes were measured using non-invasive micro-test technology (NMT). The sclerotial biomass in the Low OA group increased by 66%, however, no sclerotia formed in the High OA group. The ROS fluorescence intensity increased significantly in the Low OA group but decreased considerably in the High OA group. Ca²⁺ and H₂O₂ influx significantly increased in the Low OA group, while H₂O₂ exhibited efflux in the High OA group. A higher level of oxidative stress formed in the Low OA group. Different concentrations of oxalic acid were determined to affect P. umbellatus sclerotial formation in different ways.

Biogenesis of macrofungal sclerotia: influencing factors and molecular mechanisms

Sclerotia are dense, hard tissue structures formed by asexual reproduction of fungal hyphae in adverse environmental conditions. Macrofungal sclerotia are used in medicinal materials, healthcare foods, and nutritional supplements because of their nutritional value and biologically active ingredients, which are attracting increasing attention. Over the past few decades, the influence of abiotic factors such as nutrition (e.g., carbon and nitrogen sources) and environmental conditions (e.g., temperature, pH), and of the local biotic community (e.g., concomitants) on the formation of macrofungal sclerotia has been studied. The molecular mechanisms controlling macrofungal sclerotia formation, including oxidative stress (reactive oxygen species), signal transduction (Ca²⁺ channels and mitogen-activated protein kinase pathways), and gene expression regulation (differential expression of important enzyme or structural protein genes), have also been revealed. At the end of this review, future research prospects in the field of biogenesis of macrofungal sclerotia are discussed. KEY POINTS: • We describe factors that influence biogenesis of macrofungal sclerotia. • We explain molecular mechanisms of sclerotial biogenesis. • We discuss future directions of study of macrofungal sclerotia biogenesis.

Inhibition of Trichophyton rubrum by 420-nm Intense Pulsed Light: In Vitro Activity and the Role of Nitric Oxide in Fungal Death

Trichophyton rubrum is a common dermatophyte of the skin. The aim of this experiment was to explore the role of nitric oxide (NO) in the inhibition of T. rubrum growth induced by 420-nm intense pulsed light (IPL). This study found that nitric oxide synthase (NOS) and NO levels were increased, whereas asymmetric dimethylarginine (ADMA) level, keratinase activity, and fungal viability were decreased after IPL treatment compared with the control condition in vitro. Moreover, micromorphology was damaged by IPL treatment. Fungal viability was increased, and the damage to the fungal structure was reduced after pretreatment with an NOS inhibitor (L-NMMA) compared with IPL treatment alone. Compared with IPL alone, pretreatment with L-NMMA decreased NOS expression and NO level and increased keratinase activity. We found that 420-nm IPL treatment can inhibit the growth of T. rubrum by regulating NO in vitro.

The Role of NADPH Oxidase in the Inhibition of Trichophyton rubrum by 420-nm Intense Pulsed Light

Objectives: To evaluate the effect of intense pulsed light (IPL) on Trichophyton rubrum and investigate its mechanism of action.

Methods: The viability of fungi treated with IPL alone and with IPL combined with an NADPH oxidase inhibitor (DPI) pretreatment was determined by MTT assays. The reactive oxygen species (ROS) were quantified with a DCFH-DA fluorescent probe. Malondialdehyde (MDA) content and superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities were determined by commercial kits. The transcription of the Nox gene was quantified using quantitative real-time PCR (qRT-PCR) analysis, and micromorphology was observed using scanning electron microscopy (SEM). In addition, fungal keratinase activity was detected by measuring dye release from keratin azure.

Results: The growth declined with statistical significance after 6 h of treatment (P < 0.001). The ROS and MDA content increased after IPL treatment, whereas the SOD and GSH-Px activity decreased. Nox gene expression was upregulated, and the micromorphology was damaged. Keratinase activity decreased. Fungi that received DPI pretreatment exhibited contrasting outcomes.

Conclusion: We found that 420-nm IPL significantly inhibited the growth and pathogenicity of T. rubrum in vitro. A suggested mechanism involves Nox as a factor that mediates 420-nm IPL-induced oxidative damage of T. rubrum.

SWATH label-free proteomics analyses revealed the roles of oxidative stress and antioxidant defensing system in sclerotia formation of Polyporus umbellatus

Understanding the initiation and maturing mechanisms is important for rational manipulating sclerotia differentiation and growth from hypha of Polyporus umbellatus. Proteomes in P. umbellatus sclerotia and hyphae at initial, developmental and mature phases were studied. 1391 proteins were identified by nano-liquid chromatograph-mass spectrometry (LC-MS) in Data Dependant Acquisition mode, and 1234 proteins were quantified successfully by Sequential Window Acquisition of all THeoretical fragment ion spectra-MS (SWATH-MS) technology. There were 347 differentially expressed proteins (DEPs) in sclerotia at initial phase compared with those in hypha, and the DEP profiles were dynamically changing with sclerotia growth. Oxidative stress (OS) in sclerotia at initial phase was indicated by the repressed proteins of respiratory chain, tricarboxylic acid cycle and the activation of glycolysis/gluconeogenesis pathways were determined based on DEPs. The impact of glycolysis/gluconeogenesis on sclerotium induction was further verified by glycerol addition assays, in which 5% glycerol significantly increased sclerotial differentiation rate and biomass. It can be speculated that OS played essential roles in triggering sclerotia differentiation from hypha of P. umbellatus, whereas antioxidant activity associated with glycolysis is critical for sclerotia growth. These findings reveal a mechanism for sclerotial differentiation in P. umbellatus, which may also be applicable for other fungi.

Polyporus umbellatus inhibited tumor cell proliferation and promoted tumor cell apoptosis by down-regulating AKT in breast cancer

Breast cancer (BC) is the foremost cause of cancer-related mortality in women worldwide. Polyporus umbellatus is a polysaccharide preparation of the Chinese traditional herb medicine, which has been explored as an inhibitory compounds in suppressing many cancers. And AKT has been known as an essential signaling pathway to regulate cell proliferation and apoptosis via Mdm2/p53 and Caspase-3 signaling pathways respectively. In our study, western blot, RT-PCR, immunochemical assay, immunofluorescence as well as flow cytometry were performed in vitro or in vivo to determine the effects of Polyporus umbellatus on the progression of human laryngeal cancer. First, the breast cancer cell growth, invasion and migration were inhibited, as well as the tumor volume in nude mice was down-regulated for Polyporus umbellatus use. Additionally, our data also showed that Polyporus umbellatus suppressed breast cancer cells proliferation, which was linked with the down-regulation of AKT activation by Polyporus umbellatus treatment. Mdm was inactivated while p53 was stimulated for Polyporus umbellatus administration, displaying inhibitory role in tumor growth. Furthermore, Polyporus umbellatus could up-regulate breast cancer cells in G0/G1 phase during cell cycle, and at the same time reducing cells in S phase. Also, flow cytometry and western blot assays suggested that apoptosis was induced by the administration of Polyporus umbellatus, which enhanced Caspase-3 expressions by AKT-regulated anti-apoptotic and pro-apoptotic signals. In conclusion, our data indicated that Polyporus umbellatus had a potential role in controlling human breast cancer through inhibiting tumor cell proliferation, inducing apoptosis regulated by AKT, which might provide a therapeutic strategy for breast cancer suppression in the future.

De novo assembly and transcriptome analysis of sclerotial development in Wolfiporia cocos

Wolfiporia cocos Ryvarden et Gilbertson, a well-known medicinal fungus in the Basidiomycetes, is widely distributed in East Asia. Its dried sclerotium, which is known as Fuling in China, has been used as a traditional crude drug in Chinese traditional medicine for thousand years. However, little is known about how the sclerotium is developed at the genetic level. In this study, the de novo sequencing of sclerotia of W. cocos (S1_initial stage; S2_developmental stage and S3_mature stage) was carried out by illumina HiSeq 2000 technology. 27,438 unigenes were assembled from ~30Gbp raw data, and 12,093 unigenes were significantly annotated. The analysis of expression profiles during development returned 304 differentially expressed genes (DEGs), which were clustered into four different groups according to their expression trends. Especially for the maturation stage (S3), the sclerotium exhibited a markedly different expression profile from other stages. We further showed that peroxisome, unsaturation of fatty acids and degradation pathway were respectively prevalent in S1, S2 and S3 stages as evidenced by enrichment analysis. To our knowledge, this study represents the first report of sclerotial development transcriptomics in W. cocos. The obtained results provide novel insights into the developmental biology of the sclerotia, which is helpful for future studies about cultivation and breeding of W. cocos.

De Novo Analysis of Wolfiporia cocos Transcriptome to Reveal the Differentially Expressed Carbohydrate-Active Enzymes (CAZymes) Genes During the Early Stage of Sclerotial Growth

The sclerotium of Wolfiporia cocos has been used as an edible mushroom and/or a traditional herbal medicine for centuries. W. cocos sclerotial formation is dependent on parasitism of the wood of Pinus species. Currently, the sclerotial development mechanisms of W. cocos remain largely unknown and the lack of pine resources limit the commercial production. The CAZymes (carbohydrate-active enzymes) play important roles in degradation of the plant cell wall to provide carbohydrates for fungal growth, development, and reproduction. In this study, the transcript profiles from W. cocos mycelium and 2-months-old sclerotium, the early stage of sclerotial growth, were specially analyzed using de novo sequencing technology. A total of 142,428,180 high-quality reads of mycelium and 70,594,319 high-quality reads of 2-months-old sclerotium were obtained. Additionally, differentially expressed genes from the W. cocos mycelium and 2-months-old sclerotium stages were analyzed, resulting in identification of 69 CAZymes genes which were significantly up-regulated during the early stage of sclerotial growth compared to that of in mycelium stage, and more than half of them belonged to glycosyl hydrolases (GHs) family, indicating the importance of W. cocos GHs family for degrading the pine woods. And qRT-PCR was further used to confirm the expression pattern of these up-regulated CAZymes genes. Our results will provide comprehensive CAZymes genes expression information during W. cocos sclerotial growth at the transcriptional level and will lay a foundation for functional genes studies in this fungus. In addition, our study will also facilitate the efficient use of limited pine resources, which is significant for promoting steady development of Chinese W. cocos industry.

Oxalic acid and sclerotial differentiation of Polyporus umbellatus

The present investigation aimed to uncover the effects of exogenous oxalic acid during the sclerotial formation of Polyporus umbellatus, with an emphasis on determining the content of the endogenic oxalic acid in the fungus. To this end, the oxalic acid content of the vegetative mycelia, sclerotia, culture mediums and sclerotial exudate were measured using High Performance Liquid Chromatography (HPLC). Furthermore, the lipid peroxidation was estimated by detecting thiobarbituric bituric acid reactive substances (TBARS). The results showed that the exogenous oxalic acid caused a delay in sclerotial differentiation (of up to 9 or more days), suppressed the sclerotial biomass and decreased the lipid peroxidation significantly in a concentration-dependent manner. Oxalic acid was found at very low levels in the mycelia and the maltose medium, whereas it was found at high levels in the mycelia and sucrose medium. After sclerotial differentiation, oxalic acid accumulated at high levels in both the sclerotia and the sclerotial exudate. Oxalic acid was therefore found to inhibit P. umbellatus sclerotial formation.