Elicitation of secondary metabolism in Hypericum perforatum by rhizosphere bacteria and derived elicitors in seedlings and shoot cultures

Biochar-induced microbial and metabolic reprogramming enhances bioactive compound accumulation in Panax quinquefolius L

Panax quinquefolius L., with a history of over 300 years in traditional Chinese medicine, is notably rich in ginsenosides-its primary bioactive components. Although our previous study found that biochar application could enhance the content of ginsenoside Re, Rg and other contents in P. quinquefolius, its effect on the overall secondary metabolism of P. quinquefolius and its mechanism are still unclear. In this paper, the correlation between plant microbiome and secondary metabolites was studied from the perspective of plant rhizosphere microorganisms and endophytes, and the mechanism of biochar-induced metabolic reprogramming of P. quinquefolius was revealed. The results showed that biochar treatment significantly increased the accumulation of various substances in P. quinquefolius, including nucleosides, glycerophosphocholines, fatty acyls, steroidal glycosides, triterpenoids, and other bioactive compounds. Additionally, biochar treatment significantly enriched beneficial rhizosphere microorganisms such as Bacillus, Flavobacterium, and Devosia, while reducing the relative abundance of harmful fungi like Fusarium. Furthermore, it promoted endophytic Flavobacterium, Acaulospora, and Glomus, and suppressed pathogenic genera such as Plectosphaerella, Cladosporium, and Phaeosphaeria. These shifts in rhizosphere microbial community and endophytes structure and function were closely linked to the accumulation of secondary metabolites (e.g. ginsenosides Rg3, F2) in P. quinquefolius. Overall, our findings suggest that biochar may influence key endophytes and rhizosphere microorganisms to regulate the accumulation of secondary metabolites in P. quinquefolius. Therefore, this study provides valuable insights into the potential application of biochar in Chinese medicine agriculture.

Assessing the Impact of Irrigation and Biostimulants on the Yield and Quality Characteristics of Two Different St. John's Wort Cultivars in Their Second Growing Season

The perennial species Hypericum perforatum, commonly known as St. John's Wort, is well regarded for its medicinal attributes, particularly its strong anti-inflammatory and antidepressant effects. Hypericum perforatum L., commonly known as balsam, is extensively employed in both traditional and contemporary medicine due to its biological properties, although the plant's medicine distribution is limited to Europe and Asia. This study pioneers the investigation of Hypericum perforatum cultivation in a Mediterranean country, specifically Greece, focusing on the effects of irrigation and biostimulants of two distinct genotypes on quantitative (height, drug yield, essential oil yield) and qualitative (essential oil content and composition) characteristics. A field trial was conducted at the experimental farm of the Agrotechnology Department at the University of Thessaly, located in the Larissa region. This study investigated various testing varieties under different irrigation levels and biostimulant applications. The results underscore the importance of customized irrigation and biostimulant strategies in improving yield and quality during the second growing season, establishing a foundation for sustainable agricultural progress. Notably, irrigated treatments significantly increased plant height, dry biomass yield, and essential oil production per hectare. Specifically, the essential oil yields for irrigated treatments were nearly double those of rainfed treatments, with 219 kg/ha for rainfed and 407 kg/ha for irrigated. The genotype played a crucial role in influencing production potential, height, flowering, and essential oil composition, with one variety demonstrating biennial blooming and modified essential oil compounds. While irrigation positively impacted yield, it also reduced certain essential oil compounds while increasing β-pinene content. The effects of biostimulants varied based on their composition, with some enhancing and others diminishing essential oil content. Notably, the biostimulant containing algae with auxin and cytokinin (B2) proved to be the most effective in improving the therapeutic profile. This study offers valuable insights into the cultivation of H. perforatum in a Mediterranean climate, highlighting the necessity for ongoing research into native populations, irrigation levels, biostimulants, fertilization, and other factors that affect crop yield and quality characteristics.

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.

Molecular and genetic insights into secondary metabolic regulation underlying insect-pest resistance in legumes

Insect pests pose a major threat to agricultural production, resulting in significant economic losses for countries. A high infestation of insects in any given area can severely reduce crop yield and quality. This review examines the existing resources for managing insect pests and highlights alternative eco-friendly techniques to enhance insect pest resistance in legumes. Recently, the application of plant secondary metabolites has gained popularity in controlling insect attacks. Plant secondary metabolites encompass a wide range of compounds such as alkaloids, flavonoids, and terpenoids, which are often synthesized through intricate biosynthetic pathways. Classical methods of metabolic engineering involve manipulating key enzymes and regulatory genes to enhance or redirect the production of secondary metabolites in plants. Additionally, the role of genetic approaches, such as quantitative trait loci mapping, genome-wide association (GWAS) mapping, and metabolome-based GWAS in insect pest management is discussed, also, the role of precision breeding, such as genome editing technologies and RNA interference for identifying pest resistance and manipulating the genome to develop insect-resistant cultivars are explored, highlighting the positive contribution of plant secondary metabolites engineering-based resistance against insect pests. It is suggested that by understanding the genes responsible for beneficial metabolite compositions, future research might hold immense potential to shed more light on the molecular regulation of secondary metabolite biosynthesis, leading to advancements in insect-resistant traits in crop plants. In the future, the utilization of metabolic engineering and biotechnological methods may serve as an alternative means of producing biologically active, economically valuable, and medically significant compounds found in plant secondary metabolites, thereby addressing the challenge of limited availability.

Comparative Genomics and Physiological Investigations Supported Multifaceted Plant Growth-Promoting Activities in Two Hypericum perforatum L.-Associated Plant Growth-Promoting Rhizobacteria for Microbe-Assisted Cultivation

Plants are no longer considered standalone entities; instead, they harbor a diverse community of plant growth-promoting rhizobacteria (PGPR) that aid them in nutrient acquisition and can also deliver resilience. Host plants recognize PGPR in a strain-specific manner; therefore, introducing untargeted PGPR might produce unsatisfactory crop yields. Consequently, to develop a microbe-assisted Hypericum perforatum L. cultivation technique, 31 rhizobacteria were isolated from the plant's high-altitude Indian western Himalayan natural habitat and in vitro characterized for multiple plant growth-promoting attributes. Among 31 rhizobacterial isolates, 26 produced 0.59 to 85.29 μg mL-1 indole-3-acetic acid and solubilized 15.77 to 71.43 μg mL-1 inorganic phosphate; 21 produced 63.12 to 99.92% siderophore units, and 15 exhibited 103.60 to 1,296.42 nmol α-ketobutyrate mg-1 protein h-1 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity. Based on superior plant growth-promoting attributes, eight statistically significant multifarious PGPR were further evaluated for an in planta plant growth-promotion assay under poly greenhouse conditions. Plants treated with Kosakonia cowanii HypNH10 and Rahnella variigena HypNH18 showed, by significant amounts, the highest photosynthetic pigments and performance, eventually leading to the highest biomass accumulation. Comparative genome analysis and comprehensive genome mining unraveled their unique genetic features, such as adaptation to the host plant's immune system and specialized metabolites. Moreover, the strains harbor several functional genes regulating direct and indirect plant growth-promotion mechanisms through nutrient acquisition, phytohormone production, and stress alleviation. In essence, the current study endorsed strains HypNH10 and HypNH18 as cogent candidates for microbe-assisted H. perforatum cultivation by highlighting their exclusive genomic signatures, which suggest their unison, compatibility, and multifaceted beneficial interactions with their host and support the excellent plant growth-promotion performance observed in the greenhouse trial. IMPORTANCE Hypericum perforatum L. (St. John's wort) herbal preparations are among the top-selling products to treat depression worldwide. A significant portion of the overall Hypericum supply is sourced through wild collection, prompting a rapid decline in their natural stands. Crop cultivation seems lucrative, although cultivable land and its existing rhizomicrobiome are well suited for traditional crops, and its sudden introduction can create soil microbiome dysbiosis. Also, the conventional plant domestication procedures with increased reliance on agrochemicals can reduce the diversity of the associated rhizomicrobiome and plants' ability to interact with plant growth-promoting microorganisms, leading to unsatisfactory crop production alongside harmful environmental effects. Cultivating H. perforatum with crop-associated beneficial rhizobacteria can reconcile such concerns. Based on a combinatorial in vitro, in vivo plant growth-promotion assay and in silico prediction of plant growth-promoting traits, here we recommend two H. perforatum-associated PGPR, Kosakonia cowanii HypNH10 and Rahnella variigena HypNH18, to extrapolate as functional bioinoculants for H. perforatum sustainable cultivation.

Rhizobacterial compositions and their relationships with soil properties and medicinal bioactive ingredients in Cinnamomum migao

Introduction

Rhizobacterial communities and their metabolites can affect plant growth, development, and stress resistance, as well as the biosynthesis and accumulation of bioactive compounds in medicinal plants. This relationship has been well-characterized in many medicinal herbs, although much less commonly in medicinal trees.

Methods

Here, we analyzed the composition and structure of Cinnamomum migao rhizobacterial communities across nine growing regions in Yunnan, Guizhou and Guangxi, China, as well as differences in soil properties and fruit bioactive compounds.

Results

Results showed that the C. migao rhizobacterial communities exhibited high species richness, but location-specific differences in structure. Site-specific differences in soil properties and bioactive compounds were also observed. Furthermore, rhizobacterial community compositions were correlated with both soil properties and fruit bioactive compounds, metabolism-related functions were most common in C. migao rhizobacteria.

Discussion

Several bacterial genera, including Acidothermus, Acidibacter, Bryobacter, Candidatus_Solibacter, and Acidimicrobiales, potentially promote the biosynthesis and accumulation of 1,8-cineole, cypressene, limonene, and α-terpineol, Nitrospira and Alphaproteobacteria may play an inhibitory role. Finally, our results emphasized the critical role that soil pH and nitrogen levels play in driving rhizobacterial community structure, and specific functional bacteria can also counteract with soil properties, Acidibacter and Nitrospira can affect soil pH and nitrogen effectiveness. Overall, this study provides additional insight into the complex correlation of rhizosphere microorganisms with bioactive ingredients and soil properties of medicinal plants.

Does phenotyping of Hypericum secondary metabolism reveal a tolerance to biotic/abiotic stressors?

In this review we summarize the current knowledge about the changes in Hypericum secondary metabolism induced by biotic/abiotic stressors. It is known that the extreme environmental conditions activate signaling pathways leading to triggering of enzymatic and non-enzymatic defense systems, which stimulate production of secondary metabolites with antioxidant and protective effects. Due to several groups of bioactive compounds including naphthodianthrones, acylphloroglucinols, flavonoids, and phenylpropanes, the world-wide Hypericum perforatum represents a high-value medicinal crop of Hypericum genus, which belongs to the most diverse genera within flowering plants. The summary of the up-to-date knowledge reveals a relationship between the level of defense-related phenolic compounds and interspecific differences in the stress tolerance. The chlorogenic acid, and flavonoids, namely the amentoflavone, quercetin or kaempferol glycosides have been reported as the most defense-related metabolites associated with plant tolerance against stressful environment including temperature, light, and drought, in association with the biotic stimuli resulting from plant-microbe interactions. As an example, the species-specific cold-induced phenolics profiles of 10 Hypericum representatives of different provenances cultured in vitro are illustrated in the case-study. Principal component analysis revealed a relationship between the level of defense-related phenolic compounds and interspecific differences in the stress tolerance indicating a link between the provenance of Hypericum species and inherent mechanisms of cold tolerance. The underlying metabolome alterations along with the changes in the activities of ROS-scavenging enzymes, and non-enzymatic physiological markers are discussed. Given these data it can be anticipated that some Hypericum species native to divergent habitats, with interesting high-value secondary metabolite composition and predicted high tolerance to biotic/abiotic stresses would attract the attention as valuable sources of bioactive compounds for many medicinal purposes.

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.

Comparative analysis of the structure and function of rhizosphere microbiome of the Chinese medicinal herb Alisma in different regions

Rhizoma Alismatis, a commonly used traditional Chinese medicine, is the dried tuber of Alisma orientale and Alisma A. plantago-aquatica, mainly cultivated in Fujian and Sichuan provinces (China), respectively. Studies have shown that the rhizosphere microbiome is a key factor determining quality of Chinese medicinal plants. Here we applied metagenomics to investigate the rhizosphere microbiome of Alisma in Fujian and Sichuan, focusing on its structure and function and those genes involved in protostane triterpenes biosynthesis. The dominant phyla were Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria, and Gemmatimonadetes. Compared with Fujian, the rhizosphere of Sichuan has a greater α diversity and stronger microbial interactions but significantly lower relative abundance of archaea. Microbes with disease-suppressing functions were more abundant in Sichuan than Fujian, but vice versa for those with IAA-producing functions. Gemmatimonas, Anaeromyxobacter, and Pseudolabrys were the main contributors to the potential functional difference in two regions. Genes related to protostane triterpenes biosynthesis were enriched in Fujian. Steroidobacter, Pseudolabrys, Nevskia, and Nitrospira may contribute to the accumulation of protostane triterpenes in Alisma. This work fills a knowledge gap of Alisma's rhizosphere microbiome, providing a valuable reference for studying its beneficial microorganisms.

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

Plants and microbes interact with each other via different chemical signaling pathways. At the risophere level, the microbes can secrete molecules, called elicitors, which act on their receptors located in plant cells. The so-called elicitor molecules as well as their actions differ according to the mcirobes and induce different bilogical responses in plants such as the synthesis of secondary metabolites. Microbial compounds induced phenotype changes in plants are known as elicitors and signaling pathways which integrate elicitor's signals in plants are called elicitation. In this review, the impact of microbial elicitors on the synthesis and the secretion of secondary metabolites in plants was highlighted. Moreover, biological properties of these bioactive compounds were also highlighted and discussed. Indeed, several bacteria, fungi, and viruses release elicitors which bind to plant cell receptors and mediate signaling pathways involved in secondary metabolites synthesis. Different phytochemical classes such as terpenoids, phenolic acids and flavonoids were synthesized and/or increased in medicinal plants via the action of microbial elicitors. Moreover, these compounds compounds exhibit numerous biological activities and can therefore be explored in drugs discovery.

How to improve CHMs quality: Enlighten from CHMs ecological cultivation

Chinese herbal medicines (CHMs) are one of the important bioresources of medicine, which works by unlocking nature's ability to prevent diseases and recover from illnesses. Recently, it has ascended to the world stage and become a global icon. Nowadays, a considerable of researches have focused on the quality evaluation of CHMs. However, it is difficult to meet the reasonable needs of human beings for safe drug use to evaluate the quality of a huge number of inferior goods for the CHMs contaminated by pesticides and heavy metals. Hence to explore an eligible medicinal plant cultivation pattern, which can provide high quality CHMs sustainably, is most promising. This review analyzed the situation and characteristics of medicinal plant resources in different periods, including wild-harvested and cultivated resources during different stages, putting forward that ecological cultivation must be the way to develop medicinal plant cultivation and to obtain high quality CHMs.

Tomato Bio-Protection Induced by Pseudomonas fluorescens N21.4 Involves ROS Scavenging Enzymes and PRs, without Compromising Plant Growth

Aims: to discover the interrelationship between growth, protection and photosynthesis induced by Pseudomonas fluorescens N21.4 in tomato (Lycopersicum sculentum) challenged with the leaf pathogen Xanthomonas campestris, and to define its priming fingerprint. Methods: Photosynthesis was determined by fluorescence; plant protection was evaluated by relative disease incidence, enzyme activities by specific colorimetric assays and gene expression by qPCR. Changes in Reactive Oxygen Species (ROS) scavenging cycle enzymes and pathogenesis related protein activity and expression were determined as metabolic and genetic markers of induction of systemic resistance. Results: N21.4 significantly protected plants and increased dry weight. Growth increase is supported by significant increases in photochemical quenching together with significant decreases in energy dissipation (Non-Photochemical Quenching, NPQ). Protection was associated with changes in ROS scavenging cycle enzymes, which were significantly increased on N21.4 + pathogen challenged plants, supporting the priming effect. Superoxide Dismutase (SOD) was a good indicator of biotic stress, showing similar levels in pathogen- and N21.4-treated plants. Similarly, the activity of defense-related enzymes, ß-1,3-glucanase and chitinase significantly increased in post-pathogen challenge state; changes in gene expression were not coupled to activity. Conclusions: protection does not compromise plant growth; N21.4 priming fingerprint is defined by enhanced photochemical quenching and decreased energy dissipation, enhanced chlorophylls, primed ROS scavenging cycle enzyme activity, and glucanase and chitinase activity.

Metabolic elicitors of Pseudomonas fluorescens N 21.4 elicit flavonoid metabolism in blackberry fruit

BACKGROUND

The beneficial rhizobacterium, Pseudomonas fluorescens N 21.4, and its metabolic elicitors were inoculated in commercial cultivars of blackberry plants (Rubus cv. Loch Ness). Phenolic compounds present in red and black fruit and the expression of structural marker genes of the phenylpropanoid pathway during fruit ripening were studied.

RESULTS

An inverse relationship between gene expression and accumulation of metabolites was seen, except for the RuDFR gene, which had a direct correlation with cyanidin 3-O-glucoside synthesis, increasing its content 1.3 times when RuDFR was overexpressed in the red fruit of plants inoculated with the metabolic elicitors of P. fluorescens N 21.4, compared with red fruit of plants inoculated with N 21.4. The RuCHS gene also had a fundamental role in the accumulation of metabolites. Both rhizobacterium and metabolic elicitors triggered the flavonoid metabolism, enhancing the catechin and epicatechin content between 1.1 and 1.6 times in the case of red fruit and between 1.1 and 1.8 times in the case of black fruit. Both treatments also boosted the anthocyanin, quercetin, and kaempferol derivative content, highlighting the effects of metabolic elicitors in red fruit and the effects of live rhizobacterium in black fruit.

CONCLUSION

The metabolic elicitors' capacity to modulate gene expression and to increase secondary metabolites content was demonstrated. This work therefore suggests that they are effective, affordable, easily manageable, and ecofriendly plant inoculants that complement, or are alternatives to, beneficial rhizobacteria. © 2020 Society of Chemical Industry.

Impact of Bacillus on Phthalides Accumulation in Angelica sinensis (Oliv.) by Stoichiometry and Microbial Diversity Analysis

Plant-microorganism interaction in the rhizosphere is thought to play an important role in the formation of soil fertility, transformation and absorption of nutrients, growth and development of medicinal plants, and accumulation of medicinal ingredients. Yet, the role that they play in the phthalides accumulation of Angelica sinensis (Oliv.) Diels remains unclear. In the present study, we report a correlative analysis between rhizosphere microorganisms and phthalides accumulation in A. sinensis from Gansu, China where was the major production areas. Meanwhile, Bacillus was explored the potential functions in the plant growth and phthalide accumulation. Results revealed that the common bacterial species detected in six samples comprised 1150 OTUs which were involved in 368 genera, and predominant taxa include Actinobacteria, Acidobacteria, and Proteobacteria. The average contents of the six phthalides were 4.0329 mg/g. The correlation analysis indicated that 20 high abundance strains showed positive or negative correlations with phthalides accumulation. Flavobacterium, Nitrospira, Gaiella, Bradyrhizobium, Mycobacterium, Bacillus, RB41, Blastococcus, Nocardioides, and Solirubrobacter may be the key strains that affect phthalides accumulation on the genus level. By the plant-bacterial co-culture and fermentation, Bacillus which were isolated from rhizosphere soils can promote the plant growth, biomass accumulation and increased the contents of the butylidenephthalide (36∼415%) while the ligustilide (12∼67%) was decreased. Altogether, there is an interaction between rhizosphere microorganisms and phthalides accumulation in A. sinensis, Bacillus could promote butylidenephthalide accumulation while inhibiting ligustilide accumulation.

Induction of promising antibacterial prenylated isoflavonoids from different subclasses by sequential elicitation of soybean

Elicited soybean (Glycine max (L.) Merrill, Leguminosae) seedlings can produce prenylated isoflavonoids from different subclasses, namely pterocarpans (glyceollins), isoflavones and coumestans. These prenylated isoflavonoids serve as defence compounds and can possess antimicrobial activity. Recently, we showed that priming with reactive oxygen species (ROS) specifically stimulated the production of glyceollins in Rhizopus spp.-elicited soybean seedlings (ROS + R). In this study, we achieved diversification of the inducible subclasses of prenylated isoflavonoids in soybean, by additional stimulation of two prenylated isoflavones and one prenylated coumestan. This was achieved by using a combination of the relatively long-lived ROS representative, H2O2, with AgNO3 prior to microbial elicitation. Microbial elicitation was performed with a live preparation of either a phytopathogenic fungus, Rhizopus spp. or a symbiotic bacterium, Bacillus subtilis. B. subtilis induced 30% more prenylated isoflavones than Rhizopus spp. in (H2O2 + AgNO3)-treated seedlings, without significantly compromising the total levels of glyceollins, compared to (ROS + R)-treated seedlings. The most abundant prenylated isoflavone induced was 6-prenyl daidzein, which constituted 60% of the total isoflavones. The prenylated coumestan, phaseol, was also induced in the (H2O2 + AgNO3)-treated and microbially elicited seedlings. Based on previously developed quantitative structure-activity relationship (QSAR) models, 6-prenyl daidzein and phaseol were predicted to be promising antibacterials. Overall, we show that treatment with H2O2 and AgNO3 prior to microbial elicitation leads to the production of promising antibacterial isoflavonoids from different subclasses. Extracts rich in prenylated isoflavonoids may potentially be applied as natural antimicrobial agents.

Navarro MO, Andrade G, Lucas JA. Identifying the Compounds of the Metabolic Elicitors of Pseudomonas fluorescens N 21.4 Responsible for Their Ability to Induce Plant Resistance

In this work, the metabolic elicitors extracted from the beneficial rhizobacterium Pseudomonas fluorescens N 21.4 were sequentially fragmented by vacuum liquid chromatography to isolate, purify and identify the compounds responsible for the extraordinary capacities of this strain to induce systemic resistance and to elicit secondary defensive metabolism in diverse plant species. To check if the fractions sequentially obtained were able to increase the synthesis of isoflavones and if, therefore, they still maintained the eliciting capacity of the live strain, rapid and controlled experiments were done with soybean seeds. The optimal action concentration of the fractions was established and all of them elicited isoflavone secondary metabolism-the fractions that had been extracted with n-hexane being more effective. The purest fraction was the one with the highest eliciting capacity and was also tested in Arabidopsis thaliana seedlings to induce systemic resistance against the pathogen Pseudomonas syringae pv. tomato DC 3000. This fraction was then analyzed by UHPLC/ESI-QTOF-MS, and an alkaloid, two amino lipids, three arylalkylamines and a terpenoid were tentatively identified. These identified compounds could be part of commercial plant inoculants of biological and sustainable origin to be applied in crops, due to their potential to enhance the plant immune response and since many of them have putative antibiotic and/or antifungal potential.

Improving Flavonoid Metabolism in Blackberry Leaves and Plant Fitness by Using the Bioeffector Pseudomonas fluorescens N 21.4 and Its Metabolic Elicitors: A Biotechnological Approach for a More Sustainable Crop

Beneficial rhizobacterium Pseudomonas fluorescens N 21.4 and its metabolic elicitors inoculated to cultivars of blackberry (Rubus spp. Var. Loch Ness) reinforced the plants' immune system and improved their fitness by increasing photosynthesis, decreasing oxidative stress, and activating pathogenesis-related proteins. They also triggered the leaves' flavonoid metabolism, enhancing the accumulation of beneficial phenolic compounds such as kaempferols and quercetin derivatives. The elicitation of leaf secondary metabolism allows one to take advantage of the blackberry leaves (a current crop waste), following the premises of the circular economy, to isolate and obtain high added value compounds. The results of this work suggest the use of N 21.4 and/or its metabolic elicitors as plant inoculants as an effective and economically and environmentally friendly agronomic alternative practice in the exploitation of blackberry crops to obtain plants with a better immune system and to revalorize the leaf pruning as a potential source of polyphenols.

Plant tissue culture as a perpetual source for production of industrially important bioactive compounds

Plants have been used throughout the world for its medicinal powers since ancient time. The pharmacological properties of plants are based on their phytochemical components especially the secondary metabolites which are outstanding sources of value added bioactive compounds. Secondary metabolites have complex chemical composition and are produced in response to various forms of stress to perform different physiological tasks in plants. They are used in pharmaceutical industries, cosmetics, dietary supplements, fragrances, flavors, dyes, etc. Extended use of these metabolites in various industrial sectors has initiated a need to focus research on increasing the production by employing plant tissue culture (PTC) techniques and optimizing their large scale production using bioreactors. PTC techniques being independent of climatic and geographical conditions will provide an incessant, sustainable, economical and viable production of secondary metabolites. This review article intends to assess the advantages of using plant tissue culture, distribution of important secondary metabolites in plant families, strategies involved for optimal metabolite production and the industrial importance of selected secondary metabolites.

Biotic elicitors enhance diosgenin production in Helicteres isora L. suspension cultures via up-regulation of CAS and HMGR genes

In an attempt to find an alternative and potent source of diosgenin, a steroidal saponin in great demand for its pharmaceutical importance, Helicteres isora suspension cultures were explored for diosgenin extraction. The effect of biotic elicitors on the biosynthesis of diosgenin, in suspension cultures of H. isora was studied. Bacterial as well as fungal elicitors such as Escherichia coli, Bacillus subtilis, Saccharomyces cerevisiae and Aspergillus niger were applied at varying concentrations to investigate their effects on diosgenin content. The HPLC based quantification of the treated samples proved that amongst the biotic elicitors, E. coli (1.5%) proved best with a 9.1-fold increase in diosgenin content over respective control cultures. Further, the scaling-up of the suspension culture to shake-flask and ultimately to bioreactor level were carried out for production of diosgenin. During all the scaling-up stages, diosgenin yield obtained was in the range between 7.91 and 8.64 mg l^-1, where diosgenin content was increased with volume of the medium. The quantitative real-time PCR (qRT-PCR) analysis showed biotic elicitors induced the expression levels of regulatory genes in diosgenin biosynthetic pathway, the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) and cycloartenol synthase (CAS), which can be positively correlated with elicited diosgenin contents in those cultures. The study holds significance as H. isora represents a cleaner and easy source of diosgenin where unlike other traditional sources, it is not admixed with other steroidal saponins, and the scaled-up levels of diosgenin achieved herein have the potential to be explored commercially.

Enhanced expression of ginsenoside biosynthetic genes and in vitro ginsenoside production in elicited Panax sikkimensis (Ban) cell suspensions

Dual metabolite, i.e., ginsenoside and anthocyanin, co-accumulating cell suspensions of Panax sikkimensis were subjected to elicitation with culture filtrates of Serratia marcescens (SD 21), Bacillus subtilis (FL11), Trichoderma atroviridae (TA), and T. harzianum (TH) at 1.25% and 2.5% v/v for 1- and 3-week duration. The fungal-derived elicitors (TA and TH) did not significantly affect biomass accumulation; however, bacterial elicitors (SD 21 and FL11), especially SD 21, led to comparable loss in biomass growth. In terms of ginsenoside content, differential responses were observed. A maximum of 3.2-fold increase (222.2 mg/L) in total ginsenoside content was observed with the use of 2.5% v/v TH culture filtrate for 1 week. Similar ginsenoside accumulation was observed with the use of 1-week treatment with 2.5% v/v SD 21 culture filtrate (189.3 mg/L) with a 10-fold increase in intracellular Rg2 biosynthesis (31 mg/L). Real-time PCR analysis of key ginsenoside biosynthesis genes, i.e., FPS, SQS, DDS, PPDS, and PPTS, revealed prominent upregulation of particularly PPTS expression (20-23-fold), accounting for the observed enhancement in protopanaxatriol ginsenosides. However, none of the elicitors led to successful enhancement in in vitro anthocyanin accumulation as compared to control values.

Elicitation as a tool to improve the profiles of high-value secondary metabolites and pharmacological properties of Hypericum perforatum

OBJECTIVES

In this review, we aim at updating the available information on the improvement of the Hypericum perforatum L. (Hypericaceae) phytochemical profile and pharmacological properties via elicitation.

KEY FINDINGS

Hypericum perforatum seedlings, shoots, roots, calli and cell suspension cultures were treated with diverse elicitors to induce the formation of secondary metabolites. The extracts of the elicitor-treated plant material containing naphthodianthrones, phloroglucinols, xanthones, flavonoids and other new compounds were quantitatively analysed and tested for their bioactivities. While hypericins were mainly produced in H. perforatum cultures containing dark nodules, namely shoots and seedlings, other classes of compounds such as xanthones, phloroglucinols and flavonoids were formed in all types of cultures. The extracts obtained from elicitor-treated samples generally possessed better bioactivities compared to the extract of control biomass.

SUMMARY

Although elicitation is an excellent tool for the production of valuable secondary metabolites in H. perforatum cell and tissue cultures, its exploitation is still in its infancy mainly due to the lack of reproducibility and difficulties in scaling up biomass production.

A mechanistic insight into hydrogen peroxide-mediated elicitation of bioactive xanthones in Hoppea fastigiata shoot cultures

Elicitation of xanthones is mediated by ROS where Ca (2+) mediated generation of H 2 O 2 activates the shikimate pathway, a key regulator in early steps of xanthone biosynthesis in H. fastigiata. Shoot cultures of Hoppea fastigiata upon treatment with yeast extract (YE) accumulate an enhanced amount of 1,3,5-trihydroxy-8-methoxy xanthone. We demonstrated that YE treatment was followed by a rapid burst of reactive oxygen species (ROS, O2 (-) and H2O2) and subsequent increase in xanthone contents. The antioxidant enzymes (NADPH oxidase, superoxide dismutase (SOD), peroxidase and catalase) followed a similar kinetics as that of ROS, depending on their role in production or degradation. It was observed that shikimate dehydrogenase (SKDH) and shikimate kinase (SK) activities enhanced after 8 h, benzophenone synthase activity continued to rise after elicitation and peaked at 18 h. Activities of phenylalanine ammonia-lyase and 4-hydroxycinnamoyl-CoA ligase remained suppressed and unaffected, respectively, after elicitation. This suggests a possible phenylalanine-independent biosynthesis of xanthones. Successive treatment of shoots cultures with a NADPH-oxidase inhibitor diphenylene iodide and a ROS-scavenger dihydrolipoic acid showed inhibition in ROS (O2 (-) and H2O2) accumulation. These treatments were also shown to decrease the activities of SKDH and SK, leading to a suppressed amount of xanthones formation. Although O2 (-) showed continuous increase upon treatment with a SOD inhibitor diethyldithiocarbamic acid, the contents of H2O2 and xanthones were decreased, which correlates well with the reduced activities of SKDH and SK. Treatments with calcium antagonists, such as, lanthanum chloride and EGTA were also shown to block the activities of SKDH, SK, NADPH-oxidase and SOD, and consequently leading to suppressed accumulation of ROS (O2 (-) and H2O2) and xanthones.

Protein elicitor isolated from Escherichia coli induced bioactive compound biosynthesis as well as gene expression in Glycyrrhiza uralensis Fisch adventitious roots

This study explored the ability of three rhizobacterial strains (Bacillus subtilis, Penicillium fellutanum and Escherichia coli) to trigger metabolism.

Annual changes in bioactive contents and production in field-grown blackberry after inoculation with Pseudomonas fluorescens

The aim of this study was two-fold: first, to characterize blackberry fruits from Rubus sp. var. Lochness along the year, and secondly, to evaluate the ability of a Pseudomonas strain (N21.4) to improve fruit yield and quality under field conditions in production greenhouses throughout the year. The strain was root or leaf inoculated to blackberry plants and fruits were harvested in each season. Nutritional parameters, antioxidant potential and bioactive contents were determined; total fruit yield was recorded. Blackberries grown under short day conditions (autumn and winter) showed significantly lower °Brix values than fruits grown under long day conditions. Interestingly, an increase in fruit °Brix, relevant for quality, was detected after bacterial challenge, together with significant and sustained increases in total phenolics and flavonoids. Improvements in inoculated fruits were more evident from October through early March, when environmental conditions are worse. In summary, N21.4 is an effective agent to increase fruit quality and production along the year in blackberry; this is an environmentally friendly approach to increase fruit quality.

Plant growth-promoting rhizobacteria and root system functioning

The rhizosphere supports the development and activity of a huge and diversified microbial community, including microorganisms capable to promote plant growth. Among the latter, plant growth-promoting rhizobacteria (PGPR) colonize roots of monocots and dicots, and enhance plant growth by direct and indirect mechanisms. Modification of root system architecture by PGPR implicates the production of phytohormones and other signals that lead, mostly, to enhanced lateral root branching and development of root hairs. PGPR also modify root functioning, improve plant nutrition and influence the physiology of the whole plant. Recent results provided first clues as to how PGPR signals could trigger these plant responses. Whether local and/or systemic, the plant molecular pathways involved remain often unknown. From an ecological point of view, it emerged that PGPR form coherent functional groups, whose rhizosphere ecology is influenced by a myriad of abiotic and biotic factors in natural and agricultural soils, and these factors can in turn modulate PGPR effects on roots. In this paper, we address novel knowledge and gaps on PGPR modes of action and signals, and highlight recent progress on the links between plant morphological and physiological effects induced by PGPR. We also show the importance of taking into account the size, diversity, and gene expression patterns of PGPR assemblages in the rhizosphere to better understand their impact on plant growth and functioning. Integrating mechanistic and ecological knowledge on PGPR populations in soil will be a prerequisite to develop novel management strategies for sustainable agriculture.

Bacterial bioeffectors modify bioactive profile and increase isoflavone content in soybean sprouts (Glycine max var Osumi)

The effect of two bacterial strains to enhance bioactive contents (total phenolic compounds, total flavonoid compounds and isoflavones) and antioxidant activity on 3-day-old soybean sprouts were investigated. To identify bacterial determinants responsible for these effects, viable and UV-treated strains were delivered to wounded seeds at different concentration. Multivariate analysis performed with all the evaluated parameters indicated the different effectiveness of Stenotrophomonas maltophilia N5.18 and Pseudomonas fluorescens N21.4 based on different structural and metabolic determinants for each. N21.4 increased total phenolics and isoflavones from the genistein family, while N5.18 triggered biosynthesis of daidzein and genistein families coupled to a decrease in total phenolics, suggesting different molecular targets in the phenilpropanoid pathway. Only extracts from N5.18 treated seeds showed an improved antioxidant activity according to the β-carotene bleaching prevention method. In summary, bioeffectors from both bacterial strains are effective tools to improve soybean sprouts quality; structural elicitors from N5.18 also enhanced antioxidant activity, being the best alternative for further development of a biotechnological procedure.

Pseudomonas fluorescens N21.4 metabolites enhance secondary metabolism isoflavones in soybean (Glycine max) calli cultures

Phytopharmaceuticals are plant secondary metabolites that are strongly inducible and especially sensitive to biotic changes. Plant cell cultures are a good alternative to obtain secondary metabolites, in case effective stimulation can be achieved. In this study, metabolic elicitors from two rhizobacteria able to enhance isoflavone content in soybean seedlings were tested on three different soybean calli cell lines. Results show that metabolic elicitors from Chryseobacterium balustinum Aur9 were not effective. However, there are at least two different metabolic elicitors from Pseudomonas fluorescens N21.4, one under 10 kDa and another over 10 kDa, that trigger isoflavone metabolism in the three cell lines with different isoflavone content. Elicitors from N21.4 achieved total isoflavone increases up to 29.7% (0.205 mg/g), 64.5% (0.487 mg/g), and 23.4% (0.726 mg/g) in the low-, intermediate-, and high-yield lines, respectively. Therefore, these elicitors have a great potential to enhance isoflavone production in cell cultures for development of functional ingredients.