Regulation of sesquiterpenoid metabolism in recombinant and elicited Valeriana officinalis hairy roots

Biosynthesis of valerenic acid by engineered Saccharomyces cerevisiae

OBJECTIVE

To produce valerenic acid (VA) in Saccharomyces cerevisiae by engineering a heterologous synthetic pathway.

RESULT

Valerena-4,7(11)-diene synthase (VDS) derived from Valeriana officinalis (valerian) was expressed in S. cerevisiae to generate valerena-4,7(11)-diene as the precursor of VA. By overexpressing the key genes of the mevalonate pathway ERG8, ERG12 and ERG19, and integrating 4 copies of MBP (maltose-binding protein)-VDS-ERG20 gene expression caskets into the genome, the production of valerena-4,7(11)-diene was improved to 75 mg/L. On this basis, the cytochrome P450 monooxygenase LsGAO2 derived from Lactuca sativa was expressed to oxidize valerena-4,7(11)-diene to produce VA, and the most effective VA production strain was used for fermentation. The yield of VA reached 2.8 mg/L in the flask and 6.8 mg/L in a 5-L bioreactor fed glucose.

CONCLUSIONS

An S. cerevisiae strain was constructed and optimized to produce VA, but the valerena-4,7(11)-diene oxidation by LsGAO2 is still the rate-limiting step for VA synthesis that needs to be further optimized in future studies.

Application of metabolic engineering to enhance the content of alkaloids in medicinal plants

Plants are a rich source of bioactive compounds, many of which have been exploited for cosmetic, nutritional, and medicinal purposes. Through the characterization of metabolic pathways, as well as the mechanisms responsible for the accumulation of secondary metabolites, researchers have been able to increase the production of bioactive compounds in different plant species for research and commercial applications. The intent of the current review is to describe the metabolic engineering methods that have been used to transform in vitro or field-grown medicinal plants over the last decade and to identify the most effective approaches to increase the production of alkaloids. The articles summarized were categorized into six groups: endogenous enzyme overexpression, foreign enzyme overexpression, transcription factor overexpression, gene silencing, genome editing, and co-overexpression. We conclude that, because of the complex and multi-step nature of biosynthetic pathways, the approach that has been most commonly used to increase the biosynthesis of alkaloids, and the most effective in terms of fold increase, is the co-overexpression of two or more rate-limiting enzymes followed by the manipulation of regulatory genes.

Linking plant-root exudate changes to micropollutant exposure in aquatic plants (Lemna minor and Salvinia natans). A prospective metabolomic study

Recent findings indicate that plant-root exudates can stimulate plant-associated microorganisms to enhance the biodegradation of contaminants in constructed wetlands. To understand this process, we studied the root-exudation changes of two aquatic plants (Lemna minor and Salvinia natans) upon micropollutants exposure (10, 100 and 1000 μg/L mixes containing naproxen, diclofenac, carbamazepine, and benzotriazole). After a 2-day exposure, plant exudates were collected, extracted and non-target analysis was performed with a gas chromatography-high resolution Orbitrap mass-spectrometer. Plants didn't show morphological or growth differences between the control and spiked reactors, but exudation changes were observed in both plants at all concentration levels. Partial least squares discriminant analysis showed that, for Lemna minor, the increase of micropollutants exposure was linked to the reduction of sugar and fatty acid exudation. This may trigger changes in the microbial community living on complex carbon forms. Instead, in Salvinia natans, micropollutants exposure was linked to the release of long-chain compounds such as cuticular waxes and sesquiterpenoids, which might be related to stress signaling. These results demonstrate that plant micropollutant-exposure at environmentally relevant concentration levels triggers changes in root exudates. This may help to design new strategies to enhance micropollutants degradation in nature based solutions such as in constructed wetlands.

Structurally Guided Reprogramming of Valerenadiene Synthase

Valerena-1,10-diene synthase (VDS) catalyzes the conversion of the universal precursor farnesyl diphosphate into the unusual sesquiterpene valerena-1,10-diene (VLD), which possesses a unique isobutenyl substituent group. In planta, one of VLD's isobutenyl terminal methyl groups becomes oxidized to a carboxylic acid forming valerenic acid (VA), an allosteric modulator of the GABA_A receptor. Because a structure-activity relationship study of VA for its modulatory activity is desired, we sought to manipulate the VDS enzyme for the biosynthesis of structurally diverse scaffolds that could ultimately lead to the generation of VA analogues. Using three-dimensional structural homology models, phylogenetic sequence comparisons to well-characterized sesquiterpene synthases, and a substrate-active site contact mapping approach, the contributions of specific amino acid residues within or near the VDS active site to possible catalytic cascades for VLD and other sesquiterpene products were assessed. An essential role of Tyr535 in a germacrenyl route to VLD was demonstrated, while its contribution to a family of other sesquiterpenes derived from a humulyl route was not. No role for Cys415 or Cys452 serving as a proton donor to reaction intermediates in VLD biosynthesis was observed. However, a gatekeeper role for Asn455 in directing farnesyl carbocations down all-trans catalytic cascades (humulyl and germacrenyl routes) versus a cisoid cascade (nerolidyl route) was demonstrated. Altogether, these results have mapped residues that establish a context for the catalytic cascades operating in VDS and future manipulations for generating more structurally constrained scaffolds.

Enhanced Production of β-Caryophyllene by Farnesyl Diphosphate Precursor-Treated Callus and Hairy Root Cultures of Artemisia vulgaris L

Artemisia vulgaris L. produces a wide range of valuable secondary metabolites. The aim of the present study is to determine the effects of various concentrations of farnesyl diphosphate (FDP) on β-caryophyllene content in both callus and hairy root (HR) cultures regeneration from leaf explants of A. vulgaris L. Murashige and Skoog (MS) medium supplemented with various concentrations of 2,4-dichlorophenoxyacetic acid (2,4D; 4-13 μM), α-naphthaleneacetic acid (NAA; 5-16 μM), and FDP (1 and 3 μM) was used for callus induction and HR regeneration from leaf explants of A. vulgaris L. In this study, precursor-treated (2,4D 13.5 μM + FDP 3 μM) callus displayed the highest biomass fresh weight (FW)/dry weight (DW): 46/25 g, followed by NAA 10.7 μM + FDP 3 μM with FW/DW: 50/28 g. Two different Agrobacterium rhizogenes strains (A₄ and R₁₀₀₀) were evaluated for HR induction. The biomass of HRs induced using half-strength MS + B₅ vitamins with 3 μM FDP was FW/DW: 40/20 g and FW/DW: 41/19 g, respectively. To determine β-caryophyllene accumulation, we have isolated the essential oil from FDP-treated calli and HRs and quantified β-caryophyllene using gas chromatography-mass spectrometry (GC-MS). The highest production of β-caryophyllene was noticed in HR cultures induced using A₄ and R₁₀₀₀ strains on half-strength MS medium containing 3 μM FDP, which produced 2.92 and 2.80 mg/ml β-caryophyllene, respectively. The optimized protocol can be used commercially by scaling up the production of a β-caryophyllene compound in a short span of time.

Bioactive diterpenoid metabolism and cytotoxic activities of genetically transformed Euphorbia lathyris roots

Plants in the genus Euphorbia produce a wide variety of pharmacologically active diterpenoids with anticancer, multidrug resistance reversal, and antiviral properties. Some are the primary industrial source of ingenol mebutate, which is approved for treatment of the precancerous skin condition actinic keratosis. Similar to other high value phytochemicals, Euphorbia diterpenoids accumulate at low concentrations in planta and chemical synthesis produces similarly low yields. We established genetically transformed root cultures of Euphorbia lathryis as a strategy to gain greater access to diterpenoids from this genus. Transformed roots produced via stem explant infection with Agrobacterium rhizogenes strain 15834 recapitulated the metabolite profiles of field-grown plant roots and aerial tissues. Several putative diterpenoids were present in transformed roots, including ingenol and closely related structures, indicating that root cultures are a promising approach to Euphorbia-specific diterpenoid production. Treatment with methyl jasmonate led to a significant, albeit transient increase in mRNA levels of early diterpenoid biosynthetic enzymes (farnesyl pyrophosphate synthase, geranylgeranyl pyrophosphate synthase, and casbene synthase), suggesting that elicitation could prove useful in future pathway characterization and metabolic engineering efforts. We also show the potential of transformed E. lathyris root cultures for natural product drug discovery applications by measuring their cytotoxic activities using a panel of human carcinoma cell lines derived from prostate, cervix, breast, and lung.

Biotechnological Exploration of Transformed Root Culture for Value-Added Products

Medicinal plants produce valuable secondary metabolites with anticancer, analgesic, anticholinergic or other activities, but low metabolite levels and limited available tissue restrict metabolite yields. Transformed root cultures, also called hairy roots, provide a feasible approach for producing valuable secondary metabolites. Various strategies have been used to enhance secondary metabolite production in hairy roots, including increasing substrate availability, regulating key biosynthetic genes, multigene engineering, combining genetic engineering and elicitation, using transcription factors (TFs), and introducing new genes. In this review, we focus on recent developments in hairy roots from medicinal plants, techniques to boost production of desired secondary metabolites, and the development of new technologies to study these metabolites. We also discuss recent trends, emerging applications, and future perspectives.

Sinulaspirolactam A, a novel aza-spirocyclic valerenane sesquiterpenoid from soft coral Sinularia sp

A novel valerenane sesquiterpenoid sinulaspirolactam A (1), together with five known compounds, was isolated from the soft coral Sinularia sp. Their structures were determined by spectroscopic analyses. The absolute configuration of 1 was established by ECD calculation. Compound 1 was the first example of valerenane sesquiterpenoid bearing an aza-spiro[4.5] ring moiety, the plausible biogenetic pathway of which was proposed. Cytotoxic activities of these compounds were also evaluated.

Comparative Metabolomic and Proteomic Analyses Reveal the Regulation Mechanism Underlying MeJA-Induced Bioactive Compound Accumulation in Cutleaf Groundcherry ( Physalis angulata L.) Hairy Roots

Cutleaf groundcherry ( Physalis angulata L.) is an annual plant with a number of medicinal ingredients. However, studies about the secondary metabolism of P. angulata are very limited. An integrated metabolome and proteome approach was used to reveal the variations in the metabolism associated with bioactive compounds under methyl-jasmonate (MeJA) treatment. Application of MeJA to the hairy roots could significantly increase the accumulation of most active ingredients. A targeted approach confirmed the variations in physalins D and H between MeJA treatment and the controls. Increases in the levels of a number of terpenoid backbone biosynthesis and steroid biosynthesis related enzymes, cytochrome P450 monooxygenases and 3β-hydroxysterioid dehydrogenase might provide a potential explanation for the MeJA-induced active ingredient synthesis. Our results may contribute to a deeper understanding of the regulation mechanism underlying the MeJA-induced active compound accumulation in P. angulata.

De novo synthesis of the sedative valerenic acid in Saccharomyces cerevisiae

Valeriana officinalis (Valerian) root extracts have been used by European and Asian cultures for millennia for their anxiolytic and sedative properties. However, the efficacy of these extracts suffers from variable yields and composition, making these extracts a prime candidate for microbial production. Recently, valerenic acid, a C15 sesquiterpenoid, was identified as the active compound that modulates the GABA_A channel. Although the first committed step, valerena-4,7(11)-diene synthase, has been identified and described, the complete valerenic acid biosynthetic pathway remains to be elucidated. Sequence homology and tissue-specific expression profiles of V. officinalis putative P450s led to the discovery of a V. officinalis valerena-4,7(11)-diene oxidase, VoCYP71DJ1, which required coexpression with a V. officinalis alcohol dehydrogenase and aldehyde dehydrogenase to complete valerenic acid biosynthesis in yeast. Further, we demonstrated the stable integration of all pathway enzymes in yeast, resulting in the production of 140 mg/L of valerena-4,7(11)-diene and 4 mg/L of valerenic acid in milliliter plates. These findings showcase Saccharomyces cerevisiae's potential as an expression platform for facilitating multiply-oxidized medicinal terpenoid pathway discovery, possibly paving the way for scale up and FDA approval of valerenic acid and other active compounds from plant-derived herbal medicines.

A Chemometrics Approach to the Investigation of the Intraspecific Variability of the Volatile Oil of Eupatorium tremulum from Southern Brazil

Eupatorium tremulum is a South American shrub reported to cause cattle digestive intoxication, of which the volatile oil, mainly composed by bisabolane- and amorphane-type sesquiterpenoids, exhibits high quantitative variability. This report describes the application of chemometric tools for the identification of volatile compounds that characterize phenophasical changes in the plant. Preblooming, blooming, and postblooming specimens were paired-sampled and submitted to hydrodistillation and GC-MS analysis. Differential results were analyzed by orthogonal projection to latent structures-discriminant analysis (OPLS-DA), and the substances with different distribution in each phase were highlighted. Mean results between phases were submitted to factor analysis (FA), and correlations between the variables were demonstrated. Preblooming to blooming phase change was characterized by decreased levels of amorpha-4-en-7-ol (13) and epi-α-bisabolol (19) and increased amounts of amorpha-4,7(11)-diene (1). Blooming to postblooming change was characterized by decreases in 1, germacrene D (2), and β-bisabolene (4) and increases in 13 and 19. Finally, enhanced levels of 1, 4, and 2 reflected the change from the postblooming to the preblooming phase. FA revealed a strong correlation in the variability between the bisabolane hydrocarbons, possibly related to its common enzymatic origin. Another strong source of negative correlation showed bisabolane- and amorphane-type alcohols, on one side, and amorphane-type furans, on the other side, to occur in two alternative oxidation routes. Finally, 1 was strongly negatively correlated to its oxidized furan and ketofuran derivatives [verboccidentafuran (16) and 3-oxo-verboccidentafuran (23)] and additionally to a third compound, putatively identified as a biosynthetic intermediate between this hydrocarbon and the furans, amorpha-4,7(11)-dien-8-one (20).