Plant-microbial interaction: The mechanism and the application of microbial elicitor induced secondary metabolites biosynthesis in medicinal plants

Crosstalk between H2O2 and Ca2+ signaling is involved in root endophyte-enhanced tanshinone biosynthesis of Salvia miltiorrhiza

Tanshinones are bioactive ingredients derived from the herbal plant Salvia miltiorrhiza and are used for treating diseases of the heart and brain, thus ensuring quality of S. miltiorrhiza is paramount. Applying the endophytic fungus Trichoderma atroviride D16 can significantly increase the content of tanshinones in S. miltiorrhiza, but the potential mechanism remains unknown. In the present study, the colonization of D16 effectively enhanced the levels of Ca2+ and H2O2 in the roots of S. miltiorrhiza, which is positively correlated with increased tanshinones accumulation. Further experiments found that the treatment of plantlets with Ca2+ channel blocker (LaCl3) or H2O2 scavenger (DMTU) blocked D16-promoted tanshinones production. LaCl3 suppressed not only the D16-induced tanshinones accumulation but also the induced Ca2+ and H2O2 generation; nevertheless, DMTU did not significantly inhibit the induced Ca2+ biosynthesis, implying that Ca2+ acted upstream in H2O2 production. These results were confirmed by observations that S. miltiorrhiza treated with D16, CaCl2, and D16+LaCl3 exhibit H2O2 accumulation and influx in the roots. Moreover, H2O2 as a downstream signal of Ca2+ is involved in D16 enhanced tanshinones synthesis by inducing the expression of genes related to the biosynthesis of tanshinones, such as DXR, HMGR, GGPPS, CPS, KSL and CYP76AH1 genes. Transcriptomic analysis further supported that D16 activated the transcriptional responses related to Ca2+ and H2O2 production and tanshinones synthesis in S. miltiorrhiza seedlings. This is the first report that Ca2+ and H2O2 play important roles in regulating fungal-plant interactions thus improving the quality in the D16-S. miltiorrhiza system.

Multi-omics profiling reveal responses of three major Dendrobium species from different growth years to medicinal components

Dendrobium is a perennial herb found in Asia that is known for its medicinal and ornamental properties. Studies have shown that the stem is the primary medicinal component of Dendrobium spp. To investigate the effect of the species and age of Dendrobium (in years) on the content of its medicinal components, we collected the stems of 1-to-4-year-old D. officinale, D. moniliforme, and D. huoshanense, sequenced the transcriptome, metabolome, and microbiome, and analyzed the data in a comprehensive multi-omics study. We identified 10,426 differentially expressed genes (DEGs) with 644 differentially accumulated metabolites (DAMs) from 12 comparative groups and mapped the flavonoid pathway based on DEGs and DAMs. Transcriptomic and metabolomic data indicated a general trend of the accumulation of flavonoids exhibiting pharmacological effects in the three Dendrobium species. In addition, joint metabolome and microbiome analyses showed that actinobacteria was closely associated with flavonoid synthesis with increasing age. Our findings provide novel insights into the interactions of flavonoids of Dendrobium with the transcriptome and microbiome.

Biotechnological interventions for the production of forskolin, an active compound from the medicinal plant, Coleus forskohlii

Coleus forskohlii, an Indian-origin medicinal plant is the sole natural source of the labdane terpenoid forskolin (C22H34O7), with growing demand. Forskolin emerged as an industrially important bioactive compound, with many therapeutic applications in human health. It has established potential effects in the treatment of various diseases and conditions such as glaucoma, asthma, obesity, allergies, skin conditions and cardiovascular diseases. Moreover, clinical trials against different types of cancers are progressing. The mechanism of action of forskolin mainly involves activating adenylyl cyclase and elevating cAMP, thereby regulating different cellular processes. For the extraction of forskolin, tuberous roots of C. forskohlii are used as they contain the highest concentration of this metabolite. Approximately 2500 tonnes of the plant are cultivated annually to produce a yield of 2000-2200 kg ha-1 of dry tubers. The forskolin content of the root is distributed in the range of 0.01-1%, which cannot meet the increasing commercial demands from industries such as pharmaceuticals, cosmetics, dietary supplements, food and beverages. Hence, various aspects of micropropagation with different culture methods that employ precursors or elicitors to improve the forskolin content have been explored. Different extraction and analytical methods are also introduced to examine the yield and purity of forskolin. This review discusses the significance, clinical importance, mechanism of action and different approaches used for mass production including tissue culture for the lead compound forskolin to meet market needs.

Dynamic metabolites: A bridge between plants and microbes

Plant metabolites have a great influence on soil microbiomes. Although few studies provided insights into plant-microbe interactions, we still know very little about how plants recruit their microbiome. Here, we discuss the dynamic progress that typical metabolites shape microbes by a variety of factors, such as physiographic factors, cultivar factors, phylogeny factors, and environmental stress. Several kinds of metabolites have been reviewed, including plant primary metabolites (PPMs), phytohormones, and plant secondary metabolites (PSMs). The microbes assembled by plant metabolites in return exert beneficial effects on plants, which have been widely applied in agriculture. What's more, we point out existing problems and future research directions, such as unclear mechanisms, few species, simple parts, and ignorance of absolute abundance. This review may inspire readers to study plant-metabolite-microbe interactions in the future.

Fenchone and camphor: Main natural compounds from Lavandula stoechas L., expediting multiple in vitro biological activities

Lavandula stoechas, a Mediterranean plant, renowned in traditional medicine for its health benefits, is also arousing strong interest associated with its essential oils (EOs) with promising therapeutic properties. The aim of this study was to analyze the chemical composition of the plant, as well as to study its major activities, including antioxidant, anti-diabetic, dermatoprotective, anti-inflammatory, and antibacterial effects, focusing on its major molecules. Using the GC-MS method, the main compounds identified in L. stoechas EO (LSEO) were fenchone (31.81 %) and camphor (29.60 %), followed by terpineol (13.14 %) and menthone (8.96 %). To assess their antioxidant activity, three in vitro methods were used (DPPH, FRAP, and ABTS). The results revealed that LSEO exhibited the best antiradical property (54 ± 62 μg/mL) according to the DPPH test, while fenchone demonstrated the highest antioxidant capacity (87 ± 92 μg/mL) in the FRAP test, and camphor displayed the highest antioxidant capacity (96 ± 32 μg/mL) in the ABTS test. However, these results were lower than those obtained by Trolox used as a reference. In addition, study also explored the anti-diabetic potential of LSEO and its major compounds by evaluating their inhibitory activity towards two digestive enzymes, α-glucosidase and α-amylase. Camphor (76.92 ± 2.43 μg/mL) and fenchone (69.03 ± 2.31 μg/mL) exhibited the best inhibitory activities for α-amylase and α-glucosidase assays, respectively. Interestingly, all elements of the study exerted activities superior to those of acarbose, regardless of the test performed. In contrast, the evaluation of the dermatoprotective potential was carried out in vitro by targeting two enzymes involved in cutaneous processes, tyrosinase and elastase. In this light, fenchone (53.14 ± 3.06 μg/mL) and camphor (48.39 ± 1.92 μg/mL) were the most active against tyrosinase and elastase, respectively. It should be noted that the effect of both molecules, as well as that of LSEO, ranged between 53.14 ± 3.06 and 97.45 ± 5.22 μg/mL, which was significantly lower than the standard, quercetin (IC50 of 246.90 ± 2 0.54 μg/mL) against tyrosinase. Furthermore, the anti-inflammatory potential of these elements has been studied by evaluating their ability to inhibit lipooxygenase (LOX), a class of enzymes involved in the inflammatory process in the human body. As a result, the LSEO demonstrated a remarkable effect with an IC50 of 6.34 ± 1.29 μg/mL, which was almost comparable to the standard, quercetin (IC50 = 3.93 ± 0.45 μg/mL). Concerning the antibacterial potential, we carried out a quantitative analysis of the various products tested, revealing a bactericidal activity of the LSEO against the strain L. monocytogenes ATCC 13932 at a minimum effective concentration (MIC = CMB = 0.25). Overall, LSEOs offer significant potential as a source of natural antioxidants, and antidiabetic and anti-inflammatory agents, as well as dermatoprotective and antibacterial compounds. Its major molecules, fenchone and camphor, showed promising activity in these areas of study, making it a valuable candidate for future research and development in the field of natural medicine.

Impact of Phylogenetically Diverse Bacterial Endophytes of Bergenia pacumbis on Bergenin Production in the Plant Cell Suspension Cultures

Plant in vitro cultures are potential sources for secondary metabolites. However, low productivity is often a major drawback for industrial application. Elicitation is an important strategy to improve product formation in vitro. In this context, endophytes are of special interest as biotic elicitors due to their possible interaction with the metabolism of the host plant. A total of 128 bacterial endophytes were isolated from the medicinal plant Bergenia pacumbis and taxonomically classified using 16S rRNA gene sequencing. Five strains belonging to different genera were grown in lysogeny broth and tryptic soy broth medium and cells as well as spent media were used as elicitors in cell suspension cultures of B. pacumbis. Production of the main bioactive compound bergenin was enhanced 3-fold (964 µg/g) after treatment with cells of Moraxella sp. or spent tryptic soy broth medium of Micrococcus sp. These results indicate that elicitation of plant cell suspension cultures with endophytic bacteria is a promising strategy for enhancing the production of desired plant metabolites.

Recent progress on the microbial mitigation of heavy metal stress in soybean: overview and implications

Plants are adapted to defend themselves through programming, reprogramming, and stress tolerance against numerous environmental stresses, including heavy metal toxicity. Heavy metal stress is a kind of abiotic stress that continuously reduces various crops' productivity, including soybeans. Beneficial microbes play an essential role in improving plant productivity as well as mitigating abiotic stress. The simultaneous effect of abiotic stress from heavy metals on soybeans is rarely explored. Moreover, reducing metal contamination in soybean seeds through a sustainable approach is extremely needed. The present article describes the initiation of heavy metal tolerance mediated by plant inoculation with endophytes and plant growth-promoting rhizobacteria, the identification of plant transduction pathways via sensing annotation, and contemporary changes from molecular to genomics. The results suggest that the inoculation of beneficial microbes plays a significant role in rescuing soybeans under heavy metal stress. They create a dynamic, complex interaction with plants via a cascade called plant-microbial interaction. It enhances stress metal tolerance via the production of phytohormones, gene expression, and secondary metabolites. Overall, microbial inoculation is essential in mediating plant protection responses to heavy metal stress produced by a fluctuating climate.

Agronomic Evaluation and Chemical Characterization of Lavandula latifolia Medik. under the Semiarid Conditions of the Spanish Southeast

Lavandula latifolia is one of the main rainfed crops of aromatic and medicinal plants produced in Spain. As a global concern, the agronomic productivity of this aromatic crop is also threatened by the consequences of imminent climate change. On this basis, the study of the agronomic production of two drought-tolerant ecotypes, after three years of cultivations practices, constitutes the main objective of the present study. For this trial, clones of the two pre-selected ecotypes, along with clones from two commercial plants (control), were grown in an experimental plot. The main results confirmed an increase in biomass and essential oil production with plant age. The essential oil chemotype defined by 1,8-cineol, linalool, and camphor was maintained over time, but a decrease in 1,8-cineol in the benefit of linalool was detected. In the phenolic profile, 14 components were identified, with salvianic acid and a rosmarinic acid derivate being the main compounds quantified. These phenolic extracts showed potent in vitro antioxidant capacity, and after the second year of cultivation practices, both phenolic compounds and antioxidant capacity remained stable. Thus, under semiarid conditions, L. latifolia drought-tolerant ecotypes reach a good level of production after the second year of crop establishment.

Accumulation of phenolic compounds and expression of phenylpropanoid biosynthesis-related genes in leaves of basil transformed with A. rhizogenes strains

Biotic factors affect the content of secondary metabolites by interfering with molecular and biochemical pathways. In the current study, A. rhizogenes strains were inoculated into basil (Ocimum basilicum) to examine the effect of plant-microbe interaction on the accumulation of monomeric phenolic metabolites and the transcript levels of selected genes involved in the biochemical synthesis of secondary compounds. Initially, the integration of the rolB gene was validated by performing PCR analysis on genomic DNA samples from the basil plant inoculated with A. rhizogenes strains. We have detected that the accumulation of mRNA transcripts linked to the biosynthesis pathway of phenolic compounds has higher transcript expression levels in the leaves of transformed basil in proportion to uninoculated plants. Basil plants inoculated with A. rhizogenes 39207 strain had higher transcript levels of CAD, C4H, TAT, FLS, EGS, HPPR, PAL, and RAS genes than other experimental groups. We have identified eleven phenolic components, and the level of rosmarinic acid, eugenol, chicoric acid, and rutin increased in the inoculated basil leaves. However, the inoculation of A. rhizogenes did not cause a change in the compounds of chlorogenic acid, methyl chavicol, cinnamic acid, quercetin, vanillic acid, and caffeic acid. In conclusion, the increase in basic secondary metabolites could be achieved by the A. rhizogenes-mediated transformation of basil plants, and especially ATCC 43057 strain may be one of the A. rhizogenes strains.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01320-w.

Optimizing elicitation strategy of salicylic acid for flavonoid and phenolic production of fed-batch cultured Oplopanax elatus adventitious roots

Oplopanax elatus is a valuable medicinal plant, but its plant resource is lacking. Adventitious root (AR) culture of O. elatus is an effective way for the production of plant materials. Salicylic acid (SA) exerts enhancement effect on metabolite synthesis in some plant cell/organ culture systems. To clarify the elicitation effect of SA on fed-batch cultured O. elatus ARs, this study investigated the effects of SA concentration, and elicitation time and duration. Results showed that flavonoid and phenolic contents, and antioxidant enzyme activity obviously increased when the fed-batch cultured ARs were treated with 100 μM SA for 4 days starting on day 35. Under this elicitation condition, total flavonoid and phenolic contents reached 387 rutin mg/g DW and 128 gallic acid mg/g DW, respectively, which were significantly (p < 0.05) higher than those in the SA-untreated control. In addition, DPPH scavenging and ABTS⁺ scavenging rates, and Fe²⁺ chelating rate also greatly increased after SA treatment, and their EC₅₀ values were 0.0117, 0.61, and 3.34mg/L, respectively, indicating the high antioxidant activity. The findings of the present study revealed that SA could be used as an elicitor to improve the flavonoid and phenolic production in fed-batch O. elatus AR culture.

Chemical Profiling and Biological Properties of Essential Oils of Lavandula stoechas L. Collected from Three Moroccan Sites: In Vitro and In Silico Investigations

The aim of this study was the determination of the chemical compounds of Lavandula stoechas essential oil from Aknol (LSEO_A), Khenifra (LSEO_K), and Beni Mellal (LSEO_B), and the in vitro investigation of their antibacterial, anticandidal, and antioxidant effects, and in silico anti-SARS-CoV-2 activity. The chemical profile of LSEO was determined using GC-MS-MS analysis, the results of which showed a qualitative and quantitative variation in the chemical composition of volatile compounds including L-fenchone, cubebol, camphor, bornyl acetate, and τ-muurolol; indicating that the biosynthesis of essential oils of Lavandula stoechas (LSEO) varied depending on the site of growth. The antioxidant activity was evaluated using the ABTS and FRAP methods, our results showed that this tested oil is endowed with an ABTS inhibitory effect and an important reducing power which varies between 4.82 ± 1.52 and 15.73 ± 3.26 mg EAA/g extract. The results of antibacterial activity of LSEO_A, LSEO_K and LSEO_B, tested against Gram-positive and Gram-negative bacteria, revealed that B. subtilis (20.66 ± 1.15-25 ± 4.35 mm), P. mirabilis (18.66 ± 1.15-18.66 ± 1.15 mm), and P. aeruginosa (13.33 ± 1.15-19 ± 1.00 mm) are the most susceptible strains to LSEO_A, LSEO_K and LSEO_B of which LSEO_B exhibits bactericidal effect against P. mirabilis. furthermore The LSEO exhibited varying degrees of anticandidal activity with an inhibition zones of 25.33 ± 0.5, 22.66 ± 2.51, and 19 ± 1 mm for LSEO_K, LSEO_B, and LSEO_A, respectively. Additionally, the in silico molecular docking process, performed using Chimera Vina and Surflex-Dock programs, indicated that LSEO could inhibit SARS-CoV-2. These important biological properties of LSEO qualify this plant as an interesting source of natural bioactive compounds with medicinal actions.

Siccibacter colletis as a member of the plant growth-promoting rhizobacteria consortium to improve faba-bean growth and alleviate phosphorus deficiency stress

The rhizosphere is a hot spot and a source of beneficial microorganisms known as plant growth-promoting rhizobacteria (PGPR). From the alfalfa (Medicago sativa) rhizosphere, 115 bacteria were isolated, and from the screening for PGP traits, 26 interesting isolates were selected as PGP rhizobacteria for the next tests. The objective of this study was to use a consortium of PGPR to enhance the growth of faba-bean under phosphate (P) deficiency by taking advantage of their ability to release phosphorus from rock phosphate (RP). Several examined strains were found to have a relatively high activity on P solubilization, auxin, siderophore, ammoniac production, antifungal activity, and the ability to tolerate hypersalinity and water stress. 16S rRNA gene sequencing of the collection revealed six different genera, including Bacillus (46.15%), Siccibacter (23.07%), and Acinetobacter (15.38%) which were identified as the most abundant. Three of the interesting strains (Siccibacter colletis, Enterobacter huaxiensis, and Pantoea sp.) showed high plant growth promotion traits and no antagonism with Rhizobium laguerreae. These three bacteria were retained to establish a rhizobia-including consortium. The inoculation of faba-bean plants with the consortium improved growth parameters as root and shoot dried biomasses and some physiological criteria (chlorophyll content and P uptake under low P availability conditions), and the increase reached 40%. Our study could be the first report of faba-bean growth promotion by a multi-strain PGPR-rhizobia consortium involving S. colletis, E. huaxiensis, and Pantoea sp. Thus, this consortium could be recommended for faba-bean inoculation, particularly under P-limiting conditions.

Oxidative Status of Medicago truncatula Seedlings after Inoculation with Rhizobacteria of the Genus Pseudomonas, Paenibacillus and Sinorhizobium

An increasing number of scientists working to raise agricultural productivity see the potential in the roots and the soil adjacent to them, together with a wealth of micro-organisms. The first mechanisms activated in the plant during any abiotic or biotic stress concern changes in the oxidative status of the plant. With this in mind, for the first time, an attempt was made to check whether the inoculation of seedlings of the model plant Medicago truncatula with rhizobacteria belonging to the genus Pseudomonas (P. brassicacearum KK5, P. corrugata KK7), Paenibacillus borealis KK4 and a symbiotic strain Sinorhizobium meliloti KK13 would change the oxidative status in the days following inoculation. Initially, an increase in H₂O₂ synthesis was observed, which led to an increase in the activity of antioxidant enzymes responsible for regulating hydrogen peroxide levels. The main enzyme involved in the reduction of H₂O₂ content in the roots was catalase. The observed changes indicate the possibility of using the applied rhizobacteria to induce processes related to plant resistance and thus to ensure protection against environmental stress factors. In the next stages, it seems reasonable to check whether the initial changes in the oxidative state affect the activation of other pathways related to plant immunity.

Cocultivation of pigeon pea hairy root cultures and Aspergillus for the enhanced production of cajaninstilbene acid

Pigeon pea hairy root cultures (PPHRCs) have been proven to be a promising alternative for the production of health-beneficial phenolic compounds, such as the most important health-promoting compound, i.e., cajaninstilbene acid (CSA). In this study, PPHRCs were cocultured with live Aspergillus fungi for further improving phenolic productivity via biological elicitation. Aspergillus oryzae CGMCC 3.951 (AO 3.951) was found to be the optimal fungus that could achieve the maximum increment of CSA (10.73-fold increase) in 42-day-old PPHRCs under the inoculum size of mycelia 0.50% and cocultivation time 36 h. More precisely, the contents of CSA in hairy roots and culture media after fungal elicitation increased by 9.87- and 62.18-fold over control, respectively. Meanwhile, the contents of flavonoid glycosides decreased, while aglycone yields increased upon AO 3.951 elicitation. Moreover, AO 3.951 could trigger the oxidative stress and pathogen defense response thus activating the expression of biosynthesis- and ABC transporter-related genes, which contributed to the intracellular accumulation and extracellular secretion of phenolic compounds (especially CSA) in PPHRCs. And PAL2, 4CL2, STS1, and I3'H were likely to be the potential key enzyme genes regulating the biosynthesis of CSA, and ABCB11X1-1, ABCB11, and ABCG24X2 were closely related to the transmembrane transport of CSA. Overall, the cocultivation approach could make PPHRCs more commercially attractive for the production of high-value phenolic compounds such as CSA and flavonoid aglycones in nutraceutical/medicinal fields. And the elucidation of crucial biosynthesis and transport genes was important for systematic metabolic engineering aimed at increasing CSA productivity. KEY POINTS: • Cocultivation of PPHRCs and live fungi was to enhance CSA production and secretion. • PPHRCs augmented CSA productivity 10.73-fold when cocultured with AO 3.951 mycelia. • Several biosynthesis and transport genes related to CSA production were clarified.

Unveiling Microbial Chemical Interactions Based on Metabolomics Approaches

Microorganisms are ubiquitous in diverse habitats and studying their chemical interactions with the environment and comprehend its complex relations with both hosts and environment, are crucial for the development of strategies to control microbial diseases. This chapter discusses the importance of studying microorganisms with agricultural benefits, using specialized metabolites as examples. Herein we highlight the challenges and opportunities in utilizing microorganisms as alternatives to synthetic pesticides and fertilizers in agriculture. Genome-guided investigations and improved analytical methodologies are necessary to characterize diverse and complex biomolecules produced by microorganisms. Predicting and isolating bioproducts based on genetic information have become a focus for researchers, aided by tools like antiSMASH, BiG-SCAPE, PRISM, and others. However, translating genomic data into practical applications can be complex. Therefore, integrating genomics, transcriptomics, and metabolomics enhances chemical characterization, aiding in discovering new metabolic pathways and specialized metabolites. Additionally, elicitation is one promising strategy to enhance beneficial metabolite production. Finally, identify and characterize microbial secondary metabolites remain challenging due to their low production, complex chemical structure characterization and different environmental factors necessary for metabolite in vitro production.

Mineral contents, antimicrobial profile, acute and chronic toxicity of the aqueous extract of Moroccan Thymus vulgaris in rodents

Moroccan flora is rich in plants used in traditional medicine, but the further scientific investigation is necessary. The aim of the research was to evaluate the nutritional content and antimicrobial activity of Moroccan Thymus vulgaris, as well as its possible acute and chronic toxicological effects on rodents. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was used to determine the mineral content. The antimicrobial activity was determined using a well-diffusion test, a minimum inhibitory concentration (MIC), and a minimum bactericidal/fungicidal concentration (MBC/MFC) assay. Acute and chronic toxicity studies were conducted in vivo on mice and rats, respectively. Following that, haematological, serum-biochemistry, and histological investigations were performed. Moroccan Thyme was shown to be a source of numerous minerals which are necessary for health promotion. All antimicrobial testing, disc diffusion, MIC, and MBC tests revealed that thyme had potent antibacterial activity against all microorganisms tested. Staphylococcus aureus was the most susceptible bacterium, followed by Salmonella enterica and Escherichia coli. Additionally, thyme exhibited great antifungal efficacy against Candida albicans. The acute toxicity results indicated that the aqueous extract of T. vulgaris is almost non-toxic when taken orally. According to the chronic toxicity study, the extract is generally safe when taken orally over an extended period of time. The biochemical and haematological characteristics of the serum and blood were within acceptable limits, and histological examination revealed no abnormalities. In conclusion, the findings of this investigation, confirm the antimicrobial efficacy of the aqueous extract of Moroccan T. vulgaris and its safety for experimental animals.

Elicitation of Hyoscyamine Production in Datura stramonium L. Plants Using Tobamoviruses

Datura stramonium L. produces tropane alkaloids, and the hyoscyamine is dominant among them. Hyoscyamine is produced by hairy root cultures in vitro derived from native plants or plants with the genetically modified biosynthetic pathway for hyoscyamine. A common procedure is extraction from cultivated plants. Elicitors for increased production can be used in both cases. Live viruses are not well known for use as elicitors, therefore, D. stramonium plants grown in soil were artificially infected with the tobamoviruses Pepper mild mottle virus (PMMoV), Tomato mosaic virus (ToMV), and Tobacco mosaic virus (TMV). Differences in the content of hyoscyamine were between capsules and roots of infected and non-infected plants. Elicitation increased content of hyoscyamine in capsules 1.23-2.34 times, compared to the control. The most effective viruses were PMMoV and ToMV (isolate PV143), which increased content to above 19 mg/g of fresh weight of a capsule. The effect of each virus elicitor was expressed also in hyoscyamine content in roots. Elicited plants contained 5.41-16.54 times more hyoscyamine in roots compared to non-elicited plants. The most effective elicitor was ToMV SL-1, which raised production above 20 mg/g fresh weight of roots. It has been shown that tobamoviruses can be used as biotic elicitors.

Interaction of Epigallocatechin Gallate and Quercetin with Spike Glycoprotein (S-Glycoprotein) of SARS-CoV-2: In Silico Study

Severe acute respiratory syndrome (SARS)-CoV-2 from the family Coronaviridae is the cause of the outbreak of severe pneumonia, known as coronavirus disease 2019 (COVID-19), which was first recognized in 2019. Various potential antiviral drugs have been presented to hinder SARS-CoV-2 or treat COVID-19 disease. Side effects of these drugs are among the main complicated issues for patients. Natural compounds, specifically primary and secondary herbal metabolites, may be considered as alternative options to provide therapeutic activity and reduce cytotoxicity. Phenolic materials such as epigallocatechin gallate (EGCG, polyphenol) and quercetin have shown antibacterial, antifungal, antiviral, anticancer, and anti-inflammatory effects in vitro and in vivo. Therefore, in this study, molecular docking was applied to measure the docking property of epigallocatechin gallate and quercetin towards the transmembrane spike (S) glycoprotein of SARS-CoV-2. Results of the present study showed Vina scores of -9.9 and -8.3 obtained for EGCG and quercetin by CB-Dock. In the case of EGCG, four hydrogen bonds of OG1, OD2, O3, and O13 atoms interacted with the Threonine (THR778) and Aspartic acid (ASP867) amino acids of the spike glycoprotein (6VSB). According to these results, epigallocatechin gallate and quercetin can be considered potent therapeutic compounds for addressing viral diseases.

Contributions of Beneficial Microorganisms in Soil Remediation and Quality Improvement of Medicinal Plants

Medicinal plants (MPs) are important resources widely used in the treatment and prevention of diseases and have attracted much attention owing to their significant antiviral, anti-inflammatory, antioxidant and other activities. However, soil degradation, caused by continuous cropping, excessive chemical fertilizers and pesticide residues and heavy metal contamination, seriously restricts the growth and quality formation of MPs. Microorganisms, as the major biota in soil, play a critical role in the restoration of the land ecosystem. Rhizosphere microecology directly or indirectly affects the growth and development, metabolic regulation and active ingredient accumulation of MPs. Microbial resources, with the advantages of economic efficiency, harmless to environment and non-toxic to organisms, have been recommended as a promising alternative to conventional fertilizers and pesticides. The introduction of beneficial microbes promotes the adaptability of MPs to adversity stress by enhancing soil fertility, inhibiting pathogens and inducing systemic resistance. On the other hand, it can improve the medicinal quality by removing soil pollutants, reducing the absorption and accumulation of harmful substances and regulating the synthesis of secondary metabolites. The ecological and economic benefits of the soil microbiome in agricultural practices are increasingly recognized, but the current understanding of the interaction between soil conditions, root exudates and microbial communities and the mechanism of rhizosphere microecology affecting the secondary metabolism of MPs is still quite limited. More research is needed to investigate the effects of the microbiome on the growth and quality of different medicinal species. Therefore, the present review summarizes the main soil issues in medicinal plant cultivation, the functions of microbes in soil remediation and plant growth promotion and the potential mechanism to further guide the use of microbial resources to promote the ecological cultivation and sustainable development of MPs.

Biotechnology and In Vitro Culture as an Alternative System for Secondary Metabolite Production

Medicinal plants are rich sources of bioactive compounds widely used as medicaments, food additives, perfumes, and agrochemicals. These secondary compounds are produced under stress conditions to carry out physiological tasks in plants. Secondary metabolites have a complex chemical structure with pharmacological properties. The widespread use of these metabolites in a lot of industrial sectors has raised the need to increase the production of secondary metabolites. Biotechnological methods of cell culture allow the conservation of plants, as well as the improvement of metabolite biosynthesis and the possibility to modify the synthesis pathways. The objective of this review is to outline the applications of different in vitro culture systems with previously reported relevant examples for the optimal production of plant-derived secondary metabolites.

Cleaner production technologies for the amelioration of soil health, biomass and secondary metabolites in Ocimum basilicum L. under Indian Western Himalaya

Ocimum basilicum L. and its derived products are primarily consumed by humans; hence, agrochemical use seems inappropriate for its cultivation. However, farmers are accustomed to using rampant inorganic fertilizers to augment crop productivity, which has unintendedly engendered severe environmental perturbations. Concomitantly, farmers will soon have to confront the challenges of growing crops under suboptimal conditions driven by global climate change. Consequently, to develop a clean, sustainable, and resilient production technology, field experiments spanning over two years (2020 and 2021) were conducted, comprising three biostimulants, viz., vermicompost (0, 4, and 8 Mg ha^-1), biofertilizer (uninoculated and inoculated), and liquid seaweed extract (without and at 7 ml L^-1) in the Indian western Himalaya for the first time. Soil health indicators, leaf photosynthetic pigments, gaseous exchange, mineral contents, essential oil (EO) quantity, and composition were evaluated. Soil microbial respiration (SMR), microbial biomass carbon (MBC), organic carbon (OC), dehydrogenase (DHA), alkaline phosphatase (ALP), and β-glucosidase activities were increased by 36.23, 83.98, 30.61, 42.69, 34.00, and 40.57%, respectively, when compared with the initial soil status. The net photosynthetic rate (Pn) was significantly increased with the highest (8 Mg ha^-1) and moderate (4 Mg ha^-1) vermicompost dosages by 13.96% and 4.56%, respectively, as compared with the unfertilized control (0 Mg ha^-1). Likewise, the biofertilizer and seaweed extract also enhanced Pn by 15.09% and 10.09%, respectively. The crop's key EO constituents, viz., methyl chavicol and linalool, were significantly improved with the highest and moderate vermicompost rates of 2.71, 9.85%, and 1.18, 5.03%, respectively. Similarly, biofertilization and seaweed application also boosted methyl chavicol and linalool by 3.29, 8.67%, and 1.93, 3.66%, respectively. In both years, significantly higher herbage (8.86 and 11.25 Mg ha^-1) and EO yield (113.78 and 154.87 kg ha^-1) were recorded with a congregate treatment of the highest vermicompost dose, biofertilizer, and liquid seaweed extract. In conclusion, the integrated use of biostimulants having complementary properties can sustainably maximize the quantity and quality of O. basilicum and concomitantly ameliorate soil health. This study can inspire scientific communities and industries to develop second-generation biostimulant products, delivering better sustainability and resilience for a renaissance in agriculture.

Enantioselectivity and mechanisms of chiral herbicide biodegradation in hydroponic systems

This study demonstrates the enantioselective removal dynamics and mechanisms of the chiral herbicide metolachlor in a hydroponic system of Phragmites australis. It presents the first work to elucidate plant-microbial driven enantioselective degradation processes of chiral chemicals. The results showed a degradation efficiency of up to 95.07 ± 2.81% in the hydroponic system driven by a notably high degradation rate constant of 0.086 d^-1. P. australis was demonstrated to rapidly increase the contribution of biodegradation pathways in the hydroponic system to 82.21 ± 4.81% within 4 d with an enantiomeric fraction (EF) drop to 0.26 ± 0.02 to favour the enantioselective degradation of S-Metolachlor (k_{S-Metolachlor} = 0.568 d^-1 and k_{R-Metolachlor} = 0.147 d^-1). Comparatively, the biodegradation pathways in the control constituted less than 25%, with an EF value of circa 0.5. However, the enantioselective biodegradation pathways exhibited complete reversal after about 4 d to favour R-Metolachlor. Plants promoted the degradation of R-Metolachlor, evidenced by an increase in EF to 0.59 ± 0.03. Nonetheless, metolachlor showed an inhibitory effect on plants reflected by the reduction of plant growth rate, chlorophyll content, and electron transport rate to -7.85 ± 1.52%, 1.33 ± 0.43 mg g^-1, 4.03 ± 1.33 μmol (m² s)^-1, respectively. However, rhizosphere microorganisms aided plants to catalyze excessive reactive oxygen species production by the antioxidant enzymes to protect plants from oxidative damage and restore their physiological activities. High-throughput analysis of microbial communities demonstrated the enrichment of Massilia (40.63%) and Pseudomonas (8.16%) in the initial stage to promote the rapid degradation of S-Metolachlor. By contrast, the proliferation of Brevundimonas (32.29%) and Pseudarthrobacter (11.03%) in the terminal stage was closely associated with the degradation of R-Metolachlor. Moreover, as symbiotic bacteria of plants, these bacteria aided plants protection from reactive oxygen damages and promoted the recovery of plant metabolic functions and photosynthesis. Overall, these results demonstrate biodegradation mediated by plant-microbe mechanisms as the main driver for the enantioselective degradation of metolachlor in hydroponic systems.

Stomata at the crossroad of molecular interaction between biotic and abiotic stress responses in plants

Increasing global food production is threatened by harsh environmental conditions along with biotic stresses, requiring massive new research into integrated stress resistance in plants. Stomata play a pivotal role in response to many biotic and abiotic stresses, but their orchestrated interactions at the molecular, physiological, and biochemical levels were less investigated. Here, we reviewed the influence of drought, pathogen, and insect herbivory on stomata to provide a comprehensive overview in the context of stomatal regulation. We also summarized the molecular mechanisms of stomatal response triggered by these stresses. To further investigate the effect of stomata-herbivore interaction at a transcriptional level, integrated transcriptome studies from different plant species attacked by different pests revealed evidence of the crosstalk between abiotic and biotic stress. Comprehensive understanding of the involvement of stomata in some plant-herbivore interactions may be an essential step towards herbivores' manipulation of plants, which provides insights for the development of integrated pest management strategies. Moreover, we proposed that stomata can function as important modulators of plant response to stress combination, representing an exciting frontier of plant science with a broad and precise view of plant biotic interactions.

The Current State of Knowledge in Biological Properties of Cirsimaritin

The search for natural plant-based products as new pharmacological alternatives to treat various human pathologies has taken on great importance for researchers and research laboratories. In this context, research has intensified to extract and identify natural molecules endowed with biological effects. The objective of this study is to review the source and pharmacological properties of cirsimaritin. The identification and isolation of this flavonoid from various natural sources, including medicinal plants such as Artemisia judaica, Cirsium japonicum, Lithocarpus dealbatus, Microtea debilis, and Ocimum sanctum, has been carried out and verified using different spectral techniques. Biological effect investigations are carried out with a wide variety of experimental models in vitro and in vivo and laboratory techniques. The results of these research works showed the biological properties of cirsimaritin including anticancer, antimicrobial, antidiabetic, antiparasitic, antioxidant, and anti-inflammatory effects. The mechanisms involved in the multiple activities of this molecule are diverse and include sub-cellular, cellular, and molecular levels. Indeed, this bioactive induces anti-inflammatory and antiproliferative effects by inhibiting cell membrane receptors, interference with signaling pathways, and inhibiting transcriptional factors such as Nf-κB involved in cell promotion and proliferation. In the light of these results, cirsimaritin appears as a promising and viable alternative natural bioactive drug to treat many pathological conditions.

Linum lewisii Adventitious and Hairy-Roots Cultures as Lignan Plant Factories

Plants synthesize specific secondary metabolites for survival, reproduction, environmental resilience, and defense. Among them, lignans are a class of polyphenols with several bioactive properties: chemopreventive, anti-inflammatory, antiviral, and antioxidant. These compounds are often extracted from field-grown plants with very low yields. To overcome these constraints, in vitro tissue cultures provide a tool to optimize large-scale production. Moreover, the use of elicitation to increase secondary metabolite production is gaining importance. The aim of this work was to develop adventitious (ARL) and hairy roots (HRL) from Linum lewisi, a species able to synthesize arylnaphthalene lignans such as justicidin B. The ARL and HRL were obtained for the first time and characterized for their phenol content, antioxidant activity, and the production of justicidin B after treatments with several elicitors and precursor feeding. Through NMR spectroscopy, other four lignans were highlighted and identified in the roots extracts. A pilot-scale bioreactor was adopted to assess the suitability of the developed root cultures for future large-scale production. The ARL and HRL cultures showed a justicidin B production higher than other Linum species cultures described up to now (75.8 mg/L and 82.2 g/L), and the production more than doubled after elicitation with MeJA.

Salt tolerant PGPR strain Priestia endophytica SK1 promotes Fenugreek growth under salt stress by inducing nitrogen assimilation and secondary metabolites

AIMS

Soil salinity is a huge obstacle in crop production worldwide. Saline soil can reduce active chemical contents in medicinal plants of Leguminosae family through crippled normal nodule function. Intensive efforts are underway to improve yield and medicinal value of leguminous herbs under salt stress condition by using benign microbes. Here, an attempt was made to explore the salt tolerant bacteria associated with rhizosphere of fenugreek plant (Trigonella foenum-graecum L.) and to evaluate their impact on host plant growth and metabolite of pharmaceutical importance.

METHODS AND RESULTS

A salt tolerant plant growth promoting rhizobacterial (PGPR) strain Priestia endophytica SK1 isolated from fenugreek rhizospheric soil, which increased biomass and metabolite content in plants grown under saline stress. SK1 bacterial application induced nodule formation and enhanced nitrogen and phosphorus content under salt (100 mM NaCl) stress as compared to control plants. H2O2 production and lipid peroxidation as a measure of stress were observed high in control plants, while a reduction in these parameters was observed in plants inoculated with SK1. In addition, a significant effect was found on the phenolic compounds and trigonelline content in fenugreek plant inoculated with SK1 bacterium. An increased trigonelline content of about 54% over uninoculated control was recorded under salt stress.

CONCLUSION

The results of this study revealed that application of salt tolerant PGPR strain P. endophytica SK1 induced nitrogen fixation machinery that leads to alleviate salt stress and improved the biosynthesis of trigonelline content in fenugreek.

SIGNIFICANCE OF THE STUDY

This study extends our understanding on significance of rhizosphere microbiome and their beneficial role in plant health under environmental stress to promote agro-eco-farming 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.

A review on transcriptomic and metabolomic responses of plants to nanopollution

Nanoparticles (NPs) are tiny substances that can exist in the soil with different forms at different concentrations. In general, they present enormous effects on the growth, physiology, and molecular responses in plants. Indeed, they can penetrate the roots, stem, and leaves via different ways like stomata, plasmodesmata, xylem, and phloem and through transporter proteins like aquaporins. Once entered the plants, NPs induce reactive oxygen species (ROS) formation, and the plants respond to ROS by stimulates the production of antioxidants and antioxidant enzymes as well as the production of various primary and secondary metabolites like flavonoids and phenolic compounds. In addition, NPs have significantly affected the distribution of mineral profiles in plants. NPs considerably affect plant growth and yield in a dose-dependent fashion. At higher concentrations, they induced potent cytotoxicity and genotoxicity and thus reduced the growth and development of plants in turn decrease the yield. NPs exert potent changes in the transcriptome and metabolome pattern of plants to counteract the ROS imposed by NPs. This review depicts the overview of transcriptomic and metabolomic responses of plants towards nanopollution.

Is the rhizosphere a source of applicable multi-beneficial microorganisms for plant enhancement?

The plant faces different pedological and climatic challenges that influence its growth and enhancement. While, plant-microbes interactions throught the rhizosphere offer several privileges to this hotspot in the service of plant, by attracting multi-beneficial mutualistic and symbiotic microorganisms as plant growth-promoting bacteria (PGPB), archaea, mycorrhizal fungi, endophytic fungi, and others…). Currently, numerous investigations showed the beneficial effects of these microbes on growth and plant health. Indeed, rhizospheric microorganisms offer to host plants the essential assimilable nutrients, stimulate the growth and development of host plants, and induce antibiotics production. They also attributed to host plants numerous phenotypes involved in the increase the resistance to abiotic and biotic stresses. The investigations and the studies on the rhizosphere can offer a way to find a biological and sustainable solution to confront these environmental problems. Therefore, the interactions between microbes and plants may lead to interesting biotechnological applications on plant improvement and the adaptation in different climates to obtain a biological sustainable agricultures without the use of chemical fertilizers.