Plant Triterpenoids Regulate Endophyte Community to Promote Medicinal Plant Schisandra sphenanthera Growth and Metabolites Accumulation

New insights into the roles of fungi and bacteria in the development of medicinal plant

BACKGROUND

The interaction between microorganisms and medicinal plants is a popular topic. Previous studies consistently reported that microorganisms were mainly considered pathogens or contaminants. However, with the development of microbial detection technology, it has been demonstrated that fungi and bacteria affect beneficially the medicinal plant production chain.

AIM OF REVIEW

Microorganisms greatly affect medicinal plants, with microbial biosynthesis a high regarded topic in medicinal plant-microbial interactions. However, it lacks a systematic review discussing this relationship. Current microbial detection technologies also have certain advantages and disadvantages, it is essential to compare the characteristics of various technologies.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review first illustrates the role of fungi and bacteria in various medicinal plant production procedures, discusses the development of microbial detection and identification technologies in recent years, and concludes with microbial biosynthesis of natural products. The relationship between fungi, bacteria, and medicinal plants is discussed comprehensively. We also propose a future research model and direction for further studies.

Regulation of Bacterial Growth and Behavior by Host Plant

Plants are associated with diverse bacteria in nature. Some bacteria are pathogens that decrease plant fitness, and others are beneficial bacteria that promote plant growth and stress resistance. Emerging evidence also suggests that plant-associated commensal bacteria collectively contribute to plant health and are essential for plant survival in nature. Bacteria with different characteristics simultaneously colonize plant tissues. Thus, plants need to accommodate bacteria that provide service to the host plants, but they need to defend against pathogens at the same time. How do plants achieve this? In this review, we summarize how plants use physical barriers, control common goods such as water and nutrients, and produce antibacterial molecules to regulate bacterial growth and behavior. Furthermore, we highlight that plants use specialized metabolites that support or inhibit specific bacteria, thereby selectively recruiting plant-associated bacterial communities and regulating their function. We also raise important questions that need to be addressed to improve our understanding of plant-bacteria interactions.

Genome-Wide Investigation of Oxidosqualene Cyclase Genes Deciphers the Genetic Basis of Triterpene Biosynthesis in Tea Plants

Triterpenoids from Camellia species comprise a diverse class of bioactive compounds with great therapeutic potential. However, triterpene biosynthesis in tea plants (Camellia sinensis) remains elusive. Here, we identified eight putative 2,3-oxidosqualene cyclase (OSC) genes (CsOSC1-8) from the tea genome and characterized the functions of five through heterologous expression in yeast and tobacco and transient overexpression in tea plants. CsOSC1 was found to be a β-amyrin synthase, whereas CsOSC4, 5, and 6 exhibited multifunctional α-amyrin synthase activity. Molecular docking and site-directed mutagenesis showed that the CsOSC6M259T/W260L double mutant yielded >40% lupeol, while the CsOSC1 W259L single mutant alone was sufficient for lupeol production. The V732F mutation in CsOSC5 altered product formation from friedelin to taraxasterol and ψ-taraxasterol. The L254 M mutation in the cycloartenol synthase CsOSC8 enhanced the catalytic activity. Our findings shed light on the molecular basis governing triterpene diversity in tea plants and offer potential avenues for OSC engineering.

Optimization of the Extraction Process and Biological Activities of Triterpenoids of Schisandra sphenanthera from Different Medicinal Parts and Growth Stages

Schisandra sphenanthera Rehd. et Wils., as a traditional Chinese medicine, has important medicinal value. In the market, the availability of the fruit of S. sphenanthera mainly relies on wild picking, but many canes and leaves are discarded during wild collection, resulting in a waste of resources. The canes and leaves of S. sphenanthera contain various bioactive ingredients and can be used as spice, tea, and medicine and so present great utilization opportunities. Therefore, it is helpful to explore the effective components and biological activities of the canes and leaves to utilize S. sphenanthera fully. In this study, the response surface method with ultrasound was used to extract the total triterpenoids from the canes and leaves of S. sphenanthera at different stages. The content of total triterpenoids in the leaves at different stages was higher than that in the canes. The total triterpenoids in the canes and leaves had strong antioxidant and antibacterial abilities. At the same time, the antibacterial activity of the total triterpenoids against Bacillus subtilis and Pseudomonas aeruginosa was stronger than that against Staphylococcus aureus and Escherichia coli. This study provides the foundation for the development and utilization of the canes and leaves that would relieve the shortage of fruit resources of S. sphenanthera.

Dietary supplementation of water extract of Eucommia ulmoides bark improved caecal microbiota and parameters of health in white-feathered broilers

Eucommia ulmoides has been used as a food and medicine homologue for a long time in China. We hypothesize that Eucommia ulmoides achieves its health-promoting effects via altering gut microbiota. Here, we investigated the effects of water extract of Eucommia ulmoides bark on caecal microbiota and growth performance, antioxidant activity, and immunity in white-feathered broilers treated for 42 days. A total of 108 one-day-old Cobb white-feathered broilers were randomly assigned to three treatment groups: control diet, 0.75% Eucommia ulmoides diet (EU Ⅰ) and 1.5% Eucommia ulmoides diet (EU Ⅱ). The results showed that EU Ⅱ treatment improved average body weight (ABW), thigh muscle quality and total length of intestines, and decreased the serum total triglycerides and total cholesterol (TC) (p < 0.05). Eucommia ulmoides supplementation increased serum superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), total antioxidant activities and content of immunoglobulins, and reduced levels of malondialdehyde and tumour necrosis factor-α (TNF-α) (p < 0.05). Moreover, the supplementation increased the diversity of caecal microbiota and reduced the pathogenic genera Escherichia Shigella and Helicobacter. The genera Ochrobactrum, Odoribater, Klebsiella, Enterobacter, Georgenia and Bifidobacterium were positively associated with the ABW, total intestinal length, serum levels of GSH-Px, SOD and immunoglobulins (p < 0.001) and negatively associated with the TC and TNF-α (p < 0.01), suggesting an association of the changes of gut microbiota and improvement of broiler health. Meanwhile, Eucommia ulmoides supplementation enriched the Kyoto Encyclopedia of Genes and Genomes pathway of exocrine secretion from the pancreas, circadian entrainment and inhibited lipopolysaccharide biosynthesis. In conclusion, Eucommia ulmoides water extract can be used as a feed additive to improve poultry industry production.

Microbial communities of Schisandra sphenanthera Rehd. et Wils. and the correlations between microbial community and the active secondary metabolites

Background

Schisandra sphenanthera Rehd. et Wils. is a plant used in traditional Chinese medicine (TCM). However, great differences exist in the content of active secondary metabolites in various parts of S. sphenanthera. Do microorganisms critically influence the accumulation of active components in different parts of S. sphenanthera?

Methods

In this study, 16S/ITS amplicon sequencing analysis was applied to unravel microbial communities in rhizospheric soil and different parts of wild S. sphenanthera. At the same time, the active secondary metabolites in different parts were detected, and the correlation between the secondary metabolites and microorganisms was analyzed.

Results

The major components identified in the essential oils were sesquiterpene and oxygenated sesquiterpenes. The contents of essential oil components in fruit were much higher than that in stem and leaf, and the dominant essential oil components were different in these parts. The dominant components of the three parts were γ-muurolene, δ-cadinol, and trans farnesol (stem); α-cadinol and neoisolongifolene-8-ol (leaf); isosapathulenol, α-santalol, cedrenol, and longiverbenone (fruit). The microbial amplicon sequences were taxonomically grouped into eight (bacteria) and seven (fungi) different phyla. Community diversity and composition analyses showed that different parts of S. sphenanthera had similar and unique microbial communities, and functional prediction analysis showed that the main functions of microorganisms were related to metabolism. Moreover, the accumulation of secondary metabolites in S. sphenanthera was closely related to the microbial community composition, especially bacteria. In endophytic bacteria, Staphylococcus and Hypomicrobium had negative effects on five secondary metabolites, among which γ-muurolene and trans farnesol were the dominant components in the stem. That is, the dominant components in stems were greatly affected by microorganisms. Our results provided a new opportunity to further understand the effects of microorganisms on the active secondary metabolites and provided a basis for further research on the sustainable utilization of S. sphenanthera.

Dynamics of Endophytic Fungal Communities Associated with Cultivated Medicinal Plants in Farmland Ecosystem

Microorganisms are an important component of global biodiversity and play an important role in plant growth and development and the protection of host plants from various biotic and abiotic stresses. However, little is known about the identities and communities of endophytic fungi inhabiting cultivated medicinal plants in the farmland ecosystem. The diversity and community composition of the endophytic fungi of cultivated medicinal plants in different hosts, tissue niches, and seasonal effects in the farmland of Northern China were examined using the next-generation sequencing technique. In addition, the ecological functions of the endophytic fungal communities were investigated by combining the sequence classification information and fungal taxonomic function annotation. A total of 1025 operational taxonomic units (OTUs) of endophytic fungi were obtained at a 97% sequence similarity level; they were dominated by Dothideomycetes and Pleosporales. Host factors (species identities and tissue niches) and season had significant effects on the community composition of endophytic fungi, and endophytic fungi assembly was shaped more strongly by host than by season. In summer, endophytic fungal diversity was higher in the root than in the leaf, whereas opposite trends were observed in winter. Network analysis showed that network connectivity was more complex in the leaf than in the root, and the interspecific relationship between endophytic fungal OTUs in the network structure was mainly positive rather than negative. The functional predications of fungi revealed that the pathotrophic types of endophytic fungi decreased and the saprotrophic types increased from summer to winter in the root, while both pathotrophic and saprotrophic types of endophytic fungi increased in the leaf. This study improves our understanding of the community composition and ecological distribution of endophytic fungi inhabiting scattered niches in the farmland ecosystem. In addition, the study provides insight into the biodiversity assessment and management of cultivated medicinal plants.

Non-rhizobial nodule endophytes improve nodulation, change root exudation pattern and promote the growth of lentil, for prospective application in fallow soil

Non-rhizobial endophytes (NREs) are active colonizers inhabiting the root nodules. Though their active role in the lentil agroecosystem is not well defined, here we observed that these NREs might promote the growth of lentils, modulate rhizospheric community structure and could be used as promising organisms for optimal use of rice fallow soil. NREs from root nodules of lentils were isolated and examined for plant growth-promoting traits, exopolysaccharide (EPS) and biofilm production, root metabolites, and the presence of nifH and nifK elements. The greenhouse experiment with the chosen NREs, i.e., Serratia plymuthica 33GS and Serratia sp. R6 significantly increased the germination rate, vigour index, development of nodules (in non-sterile soil) and fresh weight of nodules (33GS 94%, R6 61% growth) and length of the shoot (33GS 86%, R6 51.16%) as well as chlorophyll levels when compared to the uninoculated control. Scanning Electron Microscopy (SEM) revealed that both isolates could successfully colonize the roots and elicit root hair growth. The inoculation of the NREs resulted in specific changes in root exudation patterns. The plants with 33GS and R6 treatment significantly stimulated the exudation of triterpenes, fatty acids, and their methyl esters in comparison to the uninoculated plants, altering the rhizospheric microbial community structure. Proteobacteria dominated the rhizospheric microbiota in all the treatments. Treatment with 33GS or R6 also enhanced the relative abundance of other favourable microbes, including Rhizobium, Mesorhizobium, and Bradyrhizobium. The correlation network analysis of relative abundances resulted in numerous bacterial taxa, which were in cooperation with each other, having a possible role in plant growth promotion. The results indicate the significant role of NREs as plant growth promoters, which also includes their role in root exudation patterns, enhancement of soil nutrient status and modulation of rhizospheric microbiota, suggesting their prospects in sustainable, and bio-based agriculture.

Signal Molecules Regulate the Synthesis of Secondary Metabolites in the Interaction between Endophytes and Medicinal Plants

Signaling molecules act as the links and bridges between endophytes and host plants. The recognition of endophytes and host plants, the regulation of host plant growth and development, and the synthesis of secondary metabolites are not separated by the participation of signaling molecules. In this review, we summarized the types and characteristics of signaling molecules in medicinal plants and the recent processes in intracellular conduction and multi-molecular crosstalk of signaling molecules during interactions between endophytic bacteria and medicinal plants. In addition, we overviewed the molecular mechanism of signals in medical metabolite accumulation and regulation. This work provides a reference for using endophytic bacteria and medicinal plants to synthesize pharmaceutical active ingredients in a bioreactor.

Growth-Promoting Characteristics of Fungal and Bacterial Endophytes Isolated from a Drought-Tolerant Mint Species Endostemon obtusifolius (E. Mey. ex Benth.) N. E. Br

Endophytes are primarily endosymbiotic bacteria and fungi that colonize the interior tissues of their host plant. They enhance the host plant's growth and attenuate adverse effects of biological stress. Endophytic species of many indigenous plants are an untapped resource of plant growth-promoting microorganisms that can mitigate abiotic stress effects. Thus, this study aimed to isolate endophytes from the roots and leaves of the medicinal plant Endostemon obtusifolius to evaluate their in vitro growth-promoting capacities and drought tolerance and to characterize the most promising species. Twenty-six endophytes (fourteen bacteria and twelve fungi) were isolated and cultured from the roots and leaves of E. obtusifolius. All 26 endophytes produced flavonoids, and 14 strains produced phenolic compounds. Of the 11 strains that displayed good free radical scavenging capability (low IC₅₀) in the 1-1-diphenyl-1-picryhydrazyl radical scavenging assay, only three strains could not survive the highest drought stress treatment (40% polyethylene glycol). These 11 strains were all positive for ammonia and siderophore production and only one strain failed to produce hydrogen cyanide and solubilize phosphate. Seven isolates showed aminocyclopropane-1-carboxylate deaminase activity and differentially synthesized indole-3-acetic acid. Using molecular tools, two promising symbiotic, drought stress tolerant, and plant growth-enhancing endophytic species (EORB-2 and EOLF-5) were identified as Paenibacillus polymyxa and Fusarium oxysporum. The results of this study demonstrate that P. polymyxa and F. oxysporum should be further investigated for their drought stress mitigation and plant growth enhancement effects as they have the potential to be developed for use in sustainable agricultural practices.

Improved growth and metabolite accumulation in Codonopsis pilosula (Franch.) Nannf. by inoculation with the endophytic Geobacillu sp. RHBA19 and Pseudomonas fluorescens RHBA17

In this study, we focused on the plant-growth-promoting properties of two strains isolated from Codonopsis pilosula, and the effect of inoculation with different strain treatments on physiological and metabolite accumulation of C. pilosula. The strains RHBA19 and RHBA17 were isolated and identified as Geobacillu sp. and Pseudomonas fluorescens, respectively. The two strains produced indole acetic acid (IAA), siderophore, biofilm, and various exoenzymes. Based on the pot experiments, inoculation of RHBA19 (G group) and the two mixed bacteria (M group) significantly improved the growth, root development, and photosynthesis of C. pilosula. Compared with the no-inoculation group (CK), the total polysaccharide content of root in the G and M groups was dramatically enhanced by 59.27% and 96.07%, and the lobetyolin (root) improved by 58.4% and 66.0%, respectively. After inoculation with bacteria agents, the activities of antioxidant enzymes (CAT, POD, SOD) of C. pilosula increased differentially. Inoculation with two types of bacterial agents significantly increased the activities of sucrose synthase (SS) and sucrose phosphate synthase (SPS) in root, and phenylalanine ammonia lyase (PAL) in leaf of C. pilosula. In addition, the content of signaling molecules (NO and H₂O₂) in three types of tissue increased significantly. The magnitude of these results was higher with mixtures than with individual strains. These results imply that the two types of bacterial agents induce physiological metabolism changes to accumulate polysaccharides and lobetyolin by regulating stress resistance enzymes and signal molecules, especially NO and H₂O₂.

Metagenomic Insights into the Composition and Function of Microbes Associated with the Rootzone of Datura inoxia

The purpose of this paper is to elucidate the roles that microbes may be playing in the rootzone of the medicinal plant Daturainoxia. We hypothesized that the microbes associated with the Datura rootzone would be significantly different than the similar surrounding fields in composition and function. We also hypothesized that rhizospheric and endophytic microbes would be associated with similar metabolic functions to the plant rootzone they inhabited. The methods employed were microbial barcoding, tests of essential oils against antibiotic resistant bacteria and other soil bacterial isolates, 16S Next Generation Sequencing (NGS) metabarcoding, and Whole Genome Shotgun (WGS) taxonomic and functional analyses. A few of the main bacterial genera of interest that were differentially abundant in the Datura root microbiome were Flavobacterium (p = 0.007), Chitinophaga (p = 0.0007), Pedobacter (p = 6 × 10−5), Bradyhizobium (p = 1 × 10−8), and Paenibacillus (p = 1.46 × 10−6). There was significant evidence that the microbes associated with the Datura rootzone had elevated function related to bacterial chalcone synthase (p = 1.49 × 10−3) and permease genes (p < 0.003). There was some evidence that microbial functions in the Datura rootzone provided precursors to important plant bioactive molecules or were beneficial to plant growth. This is important because these compounds are phyto-protective antioxidants and are precursors to many aromatic bioactive compounds that are relevant to human health. In the context of known interactions, and current results, plants and microbes influence the flavonoid biosynthetic pathways of one other, in terms of the regulation of the phenylpropanoid pathway. This is the first study to focus on the microbial ecology of the Datura rootzone. There are possible biopharmaceutical and agricultural applications of the natural interplay that was discovered during this study of the Datura inoxia rhizosphere.

Correlations Between the Metabolome and the Endophytic Fungal Metagenome Suggests Importance of Various Metabolite Classes in Community Assembly in Horseradish (Armoracia rusticana, Brassicaceae) Roots

The plant microbiome is an increasingly intensive research area, with significance in agriculture, general plant health, and production of bioactive natural products. Correlations between the fungal endophytic communities and plant chemistry can provide insight into these interactions, and suggest key contributors on both the chemical and fungal side. In this study, roots of various horseradish (Armoracia rusticana) accessions grown under the same conditions were sampled in two consecutive years and chemically characterized using a quality controlled, untargeted metabolomics approach by LC-ESI-MS/MS. Sinigrin, gluconasturtiin, glucoiberin, and glucobrassicin were also quantified. Thereafter, a subset of roots from eight accessions (n = 64) with considerable chemical variability was assessed for their endophytic fungal community, using an ITS2 amplicon-based metagenomic approach using a custom primer with high coverage on fungi, but no amplification of host internal transcribed spacer (ITS). A set of 335 chemical features, including putatively identified flavonoids, phospholipids, peptides, amino acid derivatives, indolic phytoalexins, a glucosinolate, and a glucosinolate downstream product was detected. Major taxa in horseradish roots belonged to Cantharellales, Glomerellales, Hypocreales, Pleosporales, Saccharomycetales, and Sordariales. Most abundant genera included typical endophytes such as Plectosphaerella, Thanatephorus, Podospora, Monosporascus, Exophiala, and Setophoma. A surprising dominance of single taxa was observed for many samples. In summary, 35.23% of reads of the plant endophytic fungal microbiome correlated with changes in the plant metabolome. While the concentration of flavonoid kaempferol glycosides positively correlated with the abundance of many fungal strains, many compounds showed negative correlations with fungi including indolic phytoalexins, a putative glucosinolate but not major glucosinolates and a glutathione isothiocyanate adduct. The latter is likely an in vivo glucosinolate decomposition product important in fungal arrest. Our results show the potency of the untargeted metabolomics approach in deciphering plant-microbe interactions and depicts a complex array of various metabolite classes in shaping the endophytic fungal community.