Progress on metabolites of Astragalus medicinal plants and a new factor affecting their formation: Biotransformation of endophytic fungi.

It is generally believed that the main influencing factors of plant metabolism are genetic and environmental factors. However, the transformation and catalysis of metabolic intermediates by endophytic fungi have become a new factor and resource attracting attention in recent years. There are over 2000 precious plant species in the Astragalus genus. In the past decade, at least 303 high-value metabolites have been isolated from the Astragalus medicinal plants, including 124 saponins, 150 flavonoids, two alkaloids, six sterols, and over 20 other types of compounds. These medicinal plants contain abundant endophytic fungi with unique functions, and nearly 600 endophytic fungi with known identity have been detected, but only about 35 strains belonging to 13 genera have been isolated. Among them, at least four strains affiliated to Penicillium roseopurpureum, Alternaria eureka, Neosartorya hiratsukae, and Camarosporium laburnicola have demonstrated the ability to biotransform four saponin compounds from the Astragalus genus, resulting in the production of 66 new compounds, which have significantly enhanced our understanding of the formation of metabolites in plants of the Astragalus genus. They provide a scientific basis for improving the cultivation quality of Astragalus plants through the modification of dominant fungal endophytes or reshaping the endophytic fungal community. Additionally, they open up new avenues for the discovery of specialized, green, efficient, and sustainable biotransformation pathways for complex pharmaceutical intermediates.

"Mini-community" simulation revealed the differences of endophytic fungal communities between the above- and below-ground tissues of Ephedra sinica Stapf.

The microecology of endophytic fungi in special habitats, such as the interior of different tissues from a medicinal plant, and its effects on the formation of metabolites with different biological activities are of great importance. However, the factors affecting fungal community formation are unclear. This study is the first to utilize "mini-community" remodeling to understand the above phenomena. First, high-throughput sequencing technology was applied to explore the community composition and diversity of endophytic fungi in the above-ground tissues (Ea) and below-ground tissues (Eb) of Ephedra sinica. Second, fungi were obtained through culture-dependent technology and used for "mini-community" remodeling in vitro. Then, the effects of environmental factors, partner fungi, and plant tissue fluid (internal environment) on endophytic fungal community formation were discussed. Results showed that environmental factors played a decisive role in the selection of endophytic fungi, that is, in Ea and Eb, 93.8% and 25.3% of endophytic fungi were halophilic, respectively, and 10.6% and 60.2% fungi were sensitive to high temperature (33 °C), respectively. Meanwhile, pH had little effect on fungal communities. The internal environment of the plant host further promoted the formation of endophytic fungal communities.

The composition characteristics of endophytic communities and their relationship with metabolites profile in Ephedra sinica under wild and cultivated conditions.

Ephedra sinica is one of the most famous Chinese medicinal plants. The insufficient supply of wild resources has led to the increased use of cultivated products. However, the related medicinal quality differs significantly. Although the influence of external environment on the quality of E. sinica has been studied, the impact of endophytic microbes on it remains vague. This study characterized differential metabolites and microbial community compositions in wild and cultivated E. sinica by combining metabolomics with microbiomics, and explored the effect of endophytes on the formation of differential metabolites further. The results showed that the difference in quality between wild and cultivated E. sinica was mainly in the productions of alkaloids, flavonoids, and terpenoids. The associated endophytes had special compositional characteristics. For instance, the distribution and abundance of dominant endophytes varied between wild and cultivated E. sinica. Several endophytes had significant or highly significant correlations with the formations of ephedrine, pseudoephedrine, D-cathinone, methcathinone, coumarin, kaempferol, rhamnetin, or phenylacetic acid. This study will deepen our understanding of the plant-endophyte interactions and provide a strategy for the quality control of E. sinica products.

Transcriptional Regulatory Mechanism of Differential Metabolite Formation in Root and Stem of Ephedra sinica.

Ephedra sinica, a well-known Chinese medicinal plant, is characterized as having the opposite medicinal effect among its root and stem. However, there is a lack of understanding to differentiate the active components present in the root and stem of E. sinica, as well as the molecular mechanisms underlying the formation of the differential compounds, which has significantly hampered the further development and utilization of E. sinica resource. In this study, forty-five differential metabolic markers are affiliated to alkaloids, flavonoids, terpenoids, and organic acids between root and stem of E. sinica, and sixty genes of key enzymes are involved in their biosynthesis distributed in metabolic pathway branches such as phenylalanine metabolism, flavonoid biosynthesis and phenylpropane biosynthesis, based on combination non-targeted metabolome with transcriptome technologies. The finding revealed that the expression activity changes of these enzyme genes had a direct impact on the distinction of differential metabolic markers in the root and stem of E. sinica. This study will help to understand the molecular mechanism of the differentiation and biosynthesis of the primary active metabolites in the root and stem of E. sinica, providing a theoretical foundation for its quality control and promotion in cultivation.

Endophytic fungi and their bioactive secondary metabolites in medicinal leguminosae plants: nearly untapped medical resources.

There are many species of Chinese traditional leguminosae family plants that are well known for their medicinal applications, such as Astragalus membranaceus, Catsia tora, Glycyrrhiza uralensis, Sophora flavescens and Albacia acacia. Their unique bioactive composition and internal phenological environment contribute to the formation of specific and unique endophytic fungal communities, which are important resources for new compounds used in a variety of pharmacological activities. Nonetheless, they have not been systematically studied. In the last decade, nearly 64 genera and thousands of species of endophytic fungi have been discovered from leguminosae plants, as well as 138 secondary metabolites (with 34 new compounds) including flavonoid, alkaloids, phenol, anthraquinone, macrolide, terpenoid, phytohormone and many more. These were shown to have diverse applications and benefits, such as antibacterial, antitumor, antioxidative, immunoregulatory and neuroprotective properties. Here, we provide a summarized overview with the aim of raising awareness of endophytic fungi from medicinal leguminosae plants and providing a comprehensive review of the discoveries of new natural products that may be of medicinal and pharmaceutical importance.

The microscopic mechanism between endophytic fungi and host plants: From recognition to building stable mutually beneficial relationships.

Growing research suggests that endophytic fungi deeply affect plant physiology, development, and metabolism, which has become an indispensable subject in plant research. However, the micromolecular mechanisms remain vague due to the complexity of the interactions. This article summarizes the latest progress in the mechanism studies of the symbiotic relationships between endophytic fungi and plants. We address the aspects from signal generation, plant defense, to fungal coping strategies to establish the balanced constraint relationships between fungi and their hosts that finally form "a community of shared future." These processes do not occur in isolation but in synergy. Both endophytic fungi and their host plants contribute to establishing the stable symbiosis. New insights have been provided into a deeper understanding of the occurrence of species interactions and their applications to solving practical problems.

Biotransformation ability of endophytic fungi: from species evolution to industrial applications.

Increased understanding of the interactions between endophytic fungi and plants has led to the discovery of a new generation of chemical compounds and processes between endophytic fungi and plants. Due to the long-term co-evolution between fungal endophytes and host plants, endophytes have evolved special biotransformation abilities, which can have critical consequences on plant metabolic processes and their composition. Biotransformation or bioconversion can impact the synthesis and decomposition of hormones, sugars, amino acids, vitamins, lipids, proteins, and various secondary metabolites, including flavonoids, polysaccharides, and terpenes. Endophytic fungi produce enzymes and various bioactive secondary metabolites with industrial value and can degrade or sequester inorganic and organic small molecules and macromolecules (e.g., toxins, pollutants, heavy metals). These fungi also have the ability to cause highly selective catalytic conversion of high-value compounds in an environmentally friendly manner, which can be important for the production/innovation of bioactive molecules, food and nutrition, agriculture, and environment. This work mainly summarized recent research progress in this field, providing a reference for further research and application of fungal endophytes. KEY POINTS: •The industrial value of degradation of endophytes was summarized. • The commercial value for the pharmaceutical industry is reviewed.

Species and geographic specificity between endophytic fungi and host supported by parasitic Cynomorium songaricum and its host Nitraria tangutorum distributed in desert.

This study was aimed to investigate whether host plant species and lifestyles, and environmental conditions in the desert affect endophytic fungi composition. Endophytic fungal communities from parasitic plant Cynomorium songaricum and its host Nitraria tangutorum were investigated from three sites including Tonggu Naoer, Xilin Gaole, and Guazhou in Tengger and Badain Jaran Deserts in China using the next-generation sequencing of a ribosomal RNA gene region. Similarity and difference in endophytic fungal composition from different geographic locations were evaluated through multivariate statistical analysis. It showed that plant genetics was a deciding factor affecting endophytic fungal composition even when C. songaricum and N. tangutorum grow together tightly. Not only that, the fungal composition was also greatly affected by the local environment and rainfall. However, the distribution and richness of fungal species indicated that the geographical distance exerted little influence on characterizing the fungal composition. Overall, the findings suggested that plant species, parasitic or non-parasitic lifestyles of the plant, and local environment strongly affected the number and diversity of the endophytic fungal species, which may provide valuable insights into the microbe ecology, symbiosis specificity, and the tripartite relationship among parasitic plant, host, and endophytic fungi, especially under desert environment.

Regulation by fungal endophyte of Rhodiola crenulata from enzyme genes to metabolites based on combination of transcriptome and metabolome.

BACKGROUND: The contents of some its crucial metabolites tend to decrease when Rhodiola crenulata is cultured at low altitude. Interestingly, it was found that an endophyte, Phialocephala fortinii, could alleviate this problem. RESULTS: There were 16 151 differential genes including 14 706 up-regulated and 1445 down-regulated unigenes with significant differences (P < 0.05), and a total of 1432 metabolites exhibited statistically significant (P < 0.05) metabolic differences comprising 27 different marker metabolites which showed highly significant values of VIP > 5 and P < 0.01. Results highlight differential regulation of 20 enzymatic genes that are involved in the biosynthesis of five different marker metabolites including acetaldehyde, homocysteine, cyclopropylamine, 1-pyrrolinium and halistanol sulfate. CONCLUSIONS: The positive physiological effect of P. fortinii on R. crenulata encompasses differential regulation in carbohydrate metabolism, lipid metabolism and secondary metabolite synthesis. © 2020 Society of Chemical Industry.

A review of the phytochemistry and pharmacological activities of Ephedra herb.

Ephedra herb is a traditional Chinese medicine with a long history. Conventionally, it was used as a folk phytomedicine in many ancient medical books and traditional prescriptions. Up to date, a variety of specific ingredients have been found in Ephedra herb, mainly including alkaloids, flavonoids, tannins, polysaccharides, organic acids, volatile oils, and many other active compounds. These components from Ephedra herb account for its use as the accurate treatment of cold, cough, cardiovascular and immune system disease, cancer, microbial infection, and other diseases. Moreover, with the fast development of novel chemistry and medicine technology, new chemical constituents and pharmacological effects of Ephedra herb are increasingly identified, demonstrating their great potential for various diseases treatment. Therefore, further detailed understanding and investigation of this ancient herb will offer new opportunities to develop novel therapeutics. This study systematically reviews its progress of phytochemistry, traditional and modern pharmacology based on research data that have been reported, aiming at providing useful insight for commercial exploitation, further study and precision medication of Ephedra herb in future.

Correlation in Chemical Metabolome and Endophytic Mycobiome in Cynomorium songaricum from Different Desert Locations in China.

Cynomorium songaricum Rupr. is a valuable food and medicinal plant with functions, such as an increase in sexual function, mainly attributed to its complex secondary metabolites. However, the effect of internal microbes on metabolite production in C. songaricum is still largely unclear. In this study, the relationship between endophytes and differential secondary metabolites in C. songaricum from seven major producing regions of China were explored based on established methods of metabolomics and high-throughput sequencing. The results showed that there were 13 different marker metabolites, seven shared fungal OTUs, and numerous unshared OTUs among C. songaricum distributed at different locations in China and identified significant correlations between metabolites and endophytic fungi. Our study revealed that endophytic fungi may be one possible factor that can affect the plant secondary metabolite composition.

Secondary Metabolite Accumulation Associates with Ecological Succession of Endophytic Fungi in Cynomorium songaricum Rupr.

Cynomorium songaricum Rupr. is a rare root-parasitic plant distributed in the desert ecosystem. Little is known about the role of endophytes in accumulation of metabolites in C. songaricum. Here, the correlations between the seven active components (total sugars, flavonoids, protocatechuic acid, catechins, tannins, gallic acid, and ursolic acid) and the endophytic fungi of C. songaricum were investigated, and their causal relationships are discussed further. The results showed that the accumulation of these components and the assembly of endophytic fungi changed with different plant developmental stages. Diverse relationships including positive and negative correlation were found among chemicals and endophytic fungal operational taxonomic units based on correlation coefficient matrices, which demonstrated that the accumulation of secondary metabolites in C. songaricum is closely related to the endophytic fungal community composition. These results present new opportunities to deeply understand plant-fungal symbioses and secondary metabolite productions.

Partitioning of Fungal Endophyte Assemblages in Root-Parasitic Plant Cynomorium songaricum and Its Host Nitraria tangutorum.

Endophytic fungi are an integral part and even seen as host organs of plant, influencing physiology, ecology, and development of host plants. However, little is known about micro-ecosystems and functional interactions of endophytic fungi in root-parasitic interactions of Cynomorium songaricum and its host Nitraria tangutorum. Here, distribution and dynamics of endophytic fungi were objectively investigated in their associations with C. songaricum and N. tangutorum based on mycobiome studies using high-throughput sequencing. Results suggest that endophytic fungi may be exchanged between C. songaricum and its host N. tangutorum probably through haustorium, connection of xylem and phloem in the vascular system. The similarity of endophytic fungal composition between C. songaricum and parasitized N. tangutorum was 3.88% which was significantly higher than the fungal similarity of 0.10% observed between C. songaricum and non-parasitized N. tangutorum. The similarities of fungal community in parasitized N. tangutorum were much closer to C. songaricum than to the non-parasitized N. tangutorum. The composition of endophytic fungi in these associations increased in progressive developmental stages of C. songaricum from sprouting to above ground emergence, and decreased subsequently probably due to host recognition and response by fungi. However, the shared fungal operational taxonomic units (OTUs) increased among interactions of C. songaricum with parasitized and non-parasitized N. tangutorum. Studies of bioactivity on culturable endophytic fungi showed that isolates such as Fusarium spp. possess the ability to promote seed germination of C. songaricum. Our study reports for the first time the special ecological system of endophytic fungi in C. songaricum and its host N. tangutorum. Overall, we hypothesize that a deeper understanding of the sharing, movement, and role of endophytic fungi between root-parasitic plant and its host may lead to finding alternative approaches to help increase the output of ethno-pharmacologically important medicinal plants.

Fungal endophyte-induced salidroside and tyrosol biosynthesis combined with signal cross-talk and the mechanism of enzyme gene expression in Rhodiola crenulata.

Endophyte is a factor that affects the physiology and metabolism of plant. However, limited information is available on the mechanism of interaction between endophyte and plant. To investigate the effects of endophytic fungus ZPRs-R11, that is, Trimmatostroma sp., on salidroside and tyrosol accumulations in Rhodiola crenulata, signal transduction, enzyme gene expression, and metabolic pathway were investigated. Results showed that hydrogen peroxide (H2O2), nitric oxide (NO), and salicylic acid (SA) involved in fungus-induced salidroside and tyrosol accumulations. NO acted as an upstream signal of H2O2 and SA. No up- or down-stream relationship was observed, but mutual coordination existed between H2O2 and SA. Rate-limiting enzyme genes with the maximum expression activities were UDP-glucosyltransferase, tyrosine decarboxylase (TYDC), monoamine oxidase, phenylalanine ammonialyase (PAL), and cinnamic-4-hydroxylase sequentially. Nevertheless, the genes of tyrosine transaminase and pyruvate decarboxylase only indicated slightly higher activities than those in control. Thus, TYDC and PAL branches were the preferential pathways in ZPRs-R11-induced salidroside and tyrosol accumulation. Trimmatostroma sp. was a potential fungus for promoting salidroside and tyrosol accumulations. The present data also provided scientific basis for understanding complex interaction between endophytic fungus and R. crenulata.

[Interaction between endophytes and host plant and the role of endophytes in genuineness analysis of medicinal plant].

Research of plant development and metabolism has drawn lots of attention with the fast development of science of mycorrhizal biology, molecular biology and metabonomics technology. It has become one of hot fields in the study of endophytes and plant, which would affect plant 's metabolite composition. This would provide opportunity for appraising and modifying traits to medicinal plant, and would also perfect the tranditional standpoint on forming reason of medicinal plant genuineness. Here we provide a review of theory and mechanism, research and application of interaction between plant and endophyte. This review may enhance understanding of medicinal plant, and evaluating the quality of herbs in production.

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This is the first report of the distribution and genetic relationships of endophytic fungi from the parasitic plant Cynomorium songaricum and its host Nitraria tangutorum. Endophytic fungi from the root of natural N. tangutorum, parasitic plant C. songaricum and its host N. tangutorum were isolated by tissue culture, and they were identified by morphology combined with molecular barcoding based on ITS-rDNA sequence. The isolation rates, colonization rates, isolation frequency, diversity index, evenness index, similarity coefficient and genetic relationships among fungal taxa were estimated by phylogenetic analysis, and differences in fungal endophyte distribution were investigated. The results showed that a total of 49 isolates were obtained belonging to 18 different taxa. 95.9% of these taxa were in Ascomycota, and the remaining was in Basidiomycota (4.1%). The isolation rate and colonization rate of endophytic fungi were 15.3% and 25.0%, respectively. The Shannon biodiversity index was the highest in the root of natural N. tangutorum at 2.13. The simila-rity coefficient was highest between the stem of C. songaricum and the flower of C. songaricum at0.50. Fusarium was the dominant genus in N. tangutorum, while Penicillium was the primary genus in C. songaricum. The differential distribution of fungal taxa between N. tangutorum and C. songaricum suggested that the parasitic relationship influences the endophytic fungal community.

[Effect of endophytic fungus on expression of key enzyme genes in pathway of salidroside biosynthesis in Rhodiola crenulata].

One strain of endophytic fungus ZPRa-R-1 was obtained for the capacity of promoting production of salidroside in Rhodiola crenulata. To explain the mechanism of salidroside biosynthesis in host plant, eight housekeeping genes were evaluated, and the evaluation method was created for the expression activities of four key enzyme genes PAL (phenylalanine ammonia-lyase), TyDC (tyrosine decarboxylase), TAT (tyrosine transaminase), UDPGT (UDP-glucosyltransferase) referenced double reference genes in biosynthesis pathway of salidroside in R. crenulata. Stabilities of housekeeping genes were confirmed by real-time fluorescent quantitative PCR technology and three softwares including geNorm, NormFinder and BestKeeper, then relative expressions of key enzyme genes were analysized by the 2-ΔΔCt method. The results showed that the most stable gene was GAPDH, followed by PCS, and the most appropriate reference of internal genes were combination with two genes in R. crenulata inoculated with endophytic fungus ZPRa-R-1. Under symbiosis conditions, regularity changes of key enzyme genes affected by endophytic fungus ZPRa-R-1 were as follows: the relative expression activity of PAL attached to peak value, which was 4.9 times as that of control group when inoculated ten days. The relative expression of TyDC reached the maximum value, which was 2.8 times of that control after inoculating 12 days. The relative expression of UDPGT actually reach 17.1 times than that of control after inoculating 8 days. However, the relative expression of TAT was not affected by this fungus. The changes of four key enzyme genes are positively correlated with the changes of salidroside content in R. crenulata.

Diversity and antioxidant activity of culturable endophytic fungi from alpine plants of Rhodiola crenulata, R. angusta, and R. sachalinensis.

Rhodiola spp. are rare and endangered alpine plants widely used as medicines and food additives by many civilizations since ancient times. Their main effective ingredients (such as salidroside and p-tyrosol) are praised to exhibit pharmacologic effects on high-altitude sickness and possess anti-aging and other adaptogenic capacities based on their antioxidant properties. In this study, 347 endophytic fungi were isolated from R. crenulata, R. angusta, and R. sachalinensis, and the molecular diversity and antioxidant activities of these fungi were investigated for the first time. These fungi were categorized into 180 morphotypes based on cultural characteristics, and their rRNA gene ITS sequences were analyzed by BLAST search in the GenBank database. Except for 12 unidentified fungi (6.67%), all others were affiliated to at least 57 genera in 20 orders of four phyla, namely, Ascomycota (88.89%), Basidiomycota (2.78%), Zygomycota (1.11%), and Glomeromycota (0.56%), which exhibited high abundance and diversity. Antioxidant assay showed that the DPPH radical-scavenging rates of 114 isolates (63.33%) were >50%, and those of five isolates (Rct45, Rct63, Rct64, Rac76, and Rsc57) were >90%. The EC50 values of five antioxidant assays suggested significant potential of these fungi on scavenging DPPH•, O2-•, and OH• radicals, as well as scavenging nitrite and chelating Fe2+, which showed preference and selection between endophytic fungi and their hosts. Further research also provided the first evidence that Rac12 could produce salidrosides and p-tyrosol. Results suggested that versatile endophytic fungi associated with Rhodiola known as antioxidants could be exploited as potential sources of novel antioxidant products.

Stimulation of dragon's blood accumulation in Dracaena cambodiana via fungal inoculation.

Dragon's blood is a rare and precious traditional medicine used by different cultures since ancient times. However, studies on enhancing the rapid accumulation of dragon's blood in Dracaena cambodiana and determining its formation mechanism are unavailable. In this study, the activities of two fungi, namely, BJDC01 and BJDC05, and their effect on promoting the accumulation of five main compositions of dragon's blood in D. cambodiana were investigated for the first time. Results of field tests conducted for ten months indicated that the contents of Loureirin D, 4,4'-dihydroxy-2'-dimethoxychalcone, Loureirin A and Loureirin B in two fungal-inoculated materials were 1.67 to 2.85 times greater than those of natural samples, and thus were significantly higher than those of the control groups. The content of 4,4'-dihydroxy-2'6'-dimethoxydihydrochalcone in each fungal-inoculated sample was close to that of the natural sample, and was more than twice of each of the control group. By combining the results of morphological characterizations, both BJDC01 and BJDC05 can stimulate the accumulation of the compositions of dragon's blood. This stimulation may be considered as a defense response of D. cambodiana tree against the invasion of foreign fungi. Thus, this study provides a potential way of producing dragon's blood via the inoculation of two fungal elicitors.

Biotransformation of ursolic acid by Syncephalastrum racemosum CGMCC 3.2500 and anti-HCV activity.

Microbial transformation of ursolic acid (UA, 3ß-hydroxy-urs-12-en-28-oic acid, 1) by filamentous fungus Syncephalastrum racemosum CGMCC 3.2500 was conducted. Five metabolites 3ß, 7ß, 21ß-trihydroxy-urs-12-en-28-oic acid (2); 3ß, 21ß-dihydroxy-urs-11-en-28-oic acid-13-lactone (3); 1ß, 3ß, 21ß-trihydroxy-urs-12-en-28-oic acid (4); 3ß, 7ß, 21ß-trihydroxy-urs-1-en-28-oic acid-13-lactone (5); and 21-oxo-1ß, 3ß-dihydroxy-urs-12-en-28-oic acid (6) were afforded. Elucidation of the structures of these metabolites was primarily based on 1D and 2D NMR and HR-MS data. Metabolite 2 was a new compound. In addition, the anti-HCV activity of compounds 1-6 was evaluated.