Functional Characterisation of New Sesquiterpene Synthase from the Malaysian Herbal Plant, Polygonum Minus

Plant sesquiterpene lactones

Sesquiterpene lactones (STLs) are a prominent group of plant secondary metabolites predominantly found in the Asteraceae family and have multiple ecological roles and medicinal applications. This review describes the evolutionary and ecological significance of STLs, highlighting their roles in plant defence mechanisms against herbivory and as phytotoxins, alongside their function as environmental signalling molecules. We also cover the substantial role of STLs in medicine and their mode of action in health and disease. We discuss the biosynthetic pathways and the various modifications that make STLs one of the most diverse groups of metabolites. Finally, we discuss methods for identifying and predicting STL biosynthesis pathways. This article is part of the theme issue 'The evolution of plant metabolism'.

Isolation and characterisation of sesquiterpene synthase from aromatic orchid Phalaenopsis bellina (Rchb.f.) Christenson

BACKGROUND

Phalaenopsis bellina, an orchid native to Borneo, is renowned for its unique appearance. It releases distinct fragrances, which have been linked to the presence of terpenoids. However, the identification and study of sesquiterpene synthase in P. bellina remain limited. In this study, we examines the functional characterisation of terpene synthase (TPS) from P. bellina, known as PbTS, through recombinant protein expression and its manifestation in the flower.

METHODS AND RESULTS

Gene annotation of PbTS revealed that the inferred peptide sequence of PbTS comprises 1,680 bp nucleotides encoding 559 amino acids with an estimated molecular mass of 65.2 kDa and a pI value of 5.4. A similarity search against GenBank showed that PbTS shares similarities with the previously published partial sequence of P. bellina (ABW98504.1) and Phalaenopsis equestris (XP_020597359.1 and ABW98503.1). Intriguingly, the phylogenetic analysis places the PbTS gene within the TPS-a group. In silico analysis of PbTS demonstrated stable interactions with farnesyl pyrophosphate (FPP), geranyl pyrophosphate (GPP), and geranylgeranyl pyrophosphate (GGPP). To verify this activity, an in vitro enzyme assay was performed on the PbTS recombinant protein, which successfully converted FPP, GPP, and GGPP into acyclic sesquiterpene β-farnesene, yielding approximately 0.03 mg/L. Expressional analysis revealed that the PbTS transcript was highly expressed in P. bellina, but its level did not correlate with β-farnesene levels across various flowering time points and stages.

CONCLUSION

The insights gained from this study will enhance the understanding of terpenoid production in P. bellina and aid in the discovery of novel fragrance-related genes in other orchid species.

Cloning, Expression and Functional Characterization of a Novel α-Humulene Synthase, Responsible for the Formation of Sesquiterpene in Agarwood Originating from Aquilaria malaccensis

This study describes the cloning, expression and functional characterization of α-humulene synthase, responsible for the formation of the key aromatic compound α-humulene in agarwood originating from Aquilaria malaccensis. The partial sesquiterpene synthase gene from the transcriptome data of A. malaccensis was utilized for full-length gene isolation via a 3' RACE PCR. The complete gene, denoted as AmDG2, has an open reading frame (ORF) of 1671 bp and encodes for a polypeptide of 556 amino acids. In silico analysis of the protein highlighted several conserved motifs typically found in terpene synthases such as Asp-rich substrate binding (DDxxD), metal-binding residues (NSE/DTE), and cytoplasmic ER retention (RxR) motifs at their respective sites. The AmDG2 was successfully expressed in the E. coli:pET-28a(+) expression vector whereby an expected band of about 64 kDa in size was detected in the SDS-PAGE gel. In vitro enzyme assay using substrate farnesyl pyrophosphate (FPP) revealed that AmDG2 gave rise to two sesquiterpenes: α-humulene (major) and β-caryophyllene (minor), affirming its identity as α-humulene synthase. On the other hand, protein modeling performed using AlphaFold2 suggested that AmDG2 consists entirely of α-helices with short connecting loops and turns. Meanwhile, molecular docking via AutoDock Vina (Version 1.5.7) predicted that Asp307 and Asp311 act as catalytic residues in the α-humulene synthase. To our knowledge, this is the first comprehensive report on the cloning, expression and functional characterization of α-humulene synthase from agarwood originating from A. malaccensis species. These findings reveal a deeper understanding of the structure and functional properties of the α-humulene synthase and could be utilized for metabolic engineering work in the future.

Santalum Genus: phytochemical constituents, biological activities and health promoting-effects

Santalum genus belongs to the family of Santalaceae, widespread in India, Australia, Hawaii, Sri Lanka, and Indonesia, and valued as traditional medicine, rituals and modern bioactivities. Sandalwood is reported to possess a plethora of bioactive compounds such as essential oil and its components (α-santalol and β-santalol), phenolic compounds and fatty acids. These bioactives play important role in contributing towards biological activities and health-promoting effects in humans. Pre-clinical and clinical studies have shown the role of sandalwood extract as antioxidant, anti-inflammatory, antibacterial, antifungal, antiviral, neuroleptic, antihyperglycemic, antihyperlipidemic, and anticancer activities. Safety studies on sandalwood essential oil (EO) and its extracts have proven them as a safe ingredient to be utilized in health promotion. Phytoconstituents, bioactivities and traditional uses established sandalwood as one of the innovative materials for application in the pharma, food, and biomedical industry.

Bioassay Analysis and Molecular Docking Study Revealed the Potential Medicinal Activities of Active Compounds Polygonumins B, C and D from Polygonum minus (Persicaria minor)

Polygonumins B, C and D, derivative compounds of polygonumins A, were isolated from the stem of Polygonum minus. Based on NMR results, the structure of polygonumins derivatives is comprised of four phenylpropanoid units and a sucrose unit, with a similar structure to polygonumins A. However, the structural differences between polygonumins B (1), C (2) and D (3) can be distinguished based on the existence of methoxy, ethanoyl and hydroxyl groups and protons which bind to C-4, C-4′ and C-3″. Interestingly, these bioactive compounds showed various medicinal properties based on our investigation on antioxidant, anticholinesterase and anti-HIV-1 protease activities. The IC50 value of DPPH and ABTS (antioxidant activities) was in the following descending order: polygonumins B > polygonumins C > polygonumins A > polygonumins D. In addition, almost similar pattern of antioxidant activity was observed for anti-acetylcholinesterase activity based on its IC50 value in descending order: polygonumins B > polygonumins C > polygonumins D > polygonumins A. On the other hand, polygonumins C and D showed inhibition of HIV-1 protease activity more than the positive control, pepstatin A. Finally, molecular docking studies on AChE and BChE proteins were carried out in order to gain insight into the mode of interactions between these compounds and the active residues for both enzymes. These remarkable findings indicate that these compounds have potential to be developed as targeted drugs for Alzheimer’s disease or as anti-HIV drugs.

An inducible potato (E,E)-farnesol synthase confers tolerance against bacterial pathogens in potato and tobacco

Terpene synthases (TPSs) have diverse biological functions in plants. Though the roles of TPSs in herbivore defense are well established in many plant species, their role in bacterial defense has been scarce and is emerging. Through functional genomics, here we report the in planta role of potato (Solanum tuberosum) terpene synthase (StTPS18) in bacterial defense. Expression of StTPS18 was highest in leaves and was induced in response to Pseudomonas syringae and methyl jasmonate treatments. The recombinant StTPS18 exhibited bona fide (E,E)-farnesol synthase activity forming a sesquiterpenoid, (E,E)-farnesol as the sole product, utilising (E,E)-farnesyl diphosphate (FPP). Subcellular localization of GFP fusion protein revealed that StTPS18 is localized to the cytosol. Silencing and overexpression of StTPS18 in potato resulted in reduced and enhanced tolerance, respectively, to bacterial pathogens P. syringae and Ralstonia solanacearum. Bacterial growth assay using medium containing (E,E)-farnesol significantly inhibited P. syringae growth. Moreover, StTPS18 overexpressing transgenic potato and Nicotiana tabacum leaves, and (E,E)-farnesol and P. syringae infiltrated potato leaves exhibited elevated expression of sterol pathway and members of pathogenesis-related genes with enhanced phytosterol accumulation. Interestingly, enhanced phytosterols in 13 C3 -(E,E)-farnesol infiltrated potato leaves were devoid of any noticeable 13 C labeling, indicating no direct utilization of (E,E)-farnesol in phytosterols formation. Furthermore, leaves of StTPS18 overexpressing transgenic lines had no detectable (E,E)-farnesol similar to the control plant, and emitted lower levels of sesquiterpenes than the control. These findings point towards an indirect involvement of StTPS18 and its product (E,E)-farnesol in bacterial defense through upregulation of phytosterol biosynthesis and defense genes.

Streamlining Natural Products Biomanufacturing With Omics and Machine Learning Driven Microbial Engineering

Increasing demands for the supply of biopharmaceuticals have propelled the advancement of metabolic engineering and synthetic biology strategies for biomanufacturing of bioactive natural products. Using metabolically engineered microbes as the bioproduction hosts, a variety of natural products including terpenes, flavonoids, alkaloids, and cannabinoids have been synthesized through the construction and expression of known and newly found biosynthetic genes primarily from model and non-model plants. The employment of omics technology and machine learning (ML) platforms as high throughput analytical tools has been increasingly leveraged in promoting data-guided optimization of targeted biosynthetic pathways and enhancement of the microbial production capacity, thereby representing a critical debottlenecking approach in improving and streamlining natural products biomanufacturing. To this end, this mini review summarizes recent efforts that utilize omics platforms and ML tools in strain optimization and prototyping and discusses the beneficial uses of omics-enabled discovery of plant biosynthetic genes in the production of complex plant-based natural products by bioengineered microbes.

Functional diversification in the Nudix hydrolase gene family drives sesquiterpene biosynthesis in Rosa × wichurana

Roses use a non-canonical pathway involving a Nudix hydrolase, RhNUDX1, to synthesize their monoterpenes, especially geraniol. Here we report the characterization of another expressed NUDX1 gene from the rose cultivar Rosa x wichurana, RwNUDX1-2. In order to study the function of the RwNUDX1-2 protein, we analyzed the volatile profiles of an F1 progeny generated by crossing R. chinensis cv. 'Old Blush' with R. x wichurana. A correlation test of the volatilomes with gene expression data revealed that RwNUDX1-2 is involved in the biosynthesis of a group of sesquiterpenoids, especially E,E-farnesol, in addition to other sesquiterpenes. In vitro enzyme assays and heterologous in planta functional characterization of the RwNUDX1-2 gene corroborated this result. A quantitative trait locus (QTL) analysis was performed using the data of E,E-farnesol contents in the progeny and a genetic map was constructed based on gene markers. The RwNUDX1-2 gene co-localized with the QTL for E,E-farnesol content, thereby confirming its function in sesquiterpenoid biosynthesis in R. x wichurana. Finally, in order to understand the structural bases for the substrate specificity of rose NUDX proteins, the RhNUDX1 protein was crystallized, and its structure was refined to 1.7 Å. By molecular modeling of different rose NUDX1 protein complexes with their respective substrates, a structural basis for substrate discrimination by rose NUDX1 proteins is proposed.

Rahim MH, Sabri S, Lai KS, Song AAL, Abdul Rahim R, Wan Abdullah WMAN, Ong Abdullah J. Functional characterization of a new terpene synthase from Plectranthus amboinicus

Plectranthus amboinicus (Lour.) Spreng is an aromatic medicinal herb known for its therapeutic and nutritional properties attributed by the presence of monoterpene and sesquiterpene compounds. Up until now, research on terpenoid biosynthesis has focused on a few mint species with economic importance such as thyme and oregano, yet the terpene synthases responsible for monoterpene production in P. amboinicus have not been described. Here we report the isolation, heterologous expression and functional characterization of a terpene synthase involved in P. amboinicus terpenoid biosynthesis. A putative monoterpene synthase gene (PamTps1) from P. amboinicus was isolated with an open reading frame of 1797 bp encoding a predicted protein of 598 amino acids with molecular weight of 69.6 kDa. PamTps1 shares 60–70% amino acid sequence similarity with other known terpene synthases of Lamiaceae. The in vitro enzymatic activity of PamTps1 demonstrated the conversion of geranyl pyrophosphate and farnesyl pyrophosphate exclusively into linalool and nerolidol, respectively, and thus PamTps1 was classified as a linalool/nerolidol synthase. In vivo activity of PamTps1 in a recombinant Escherichia coli strain revealed production of linalool and nerolidol which correlated with its in vitro activity. This outcome validated the multi-substrate usage of this enzyme in producing linalool and nerolidol both in in vivo and in vitro systems. The transcript level of PamTps1 was prominent in the leaf during daytime as compared to the stem. Gas chromatography-mass spectrometry (GC-MS) and quantitative real-time PCR analyses showed that maximal linalool level was released during the daytime and lower at night following a diurnal circadian pattern which correlated with the PamTps1 expression pattern. The PamTps1 cloned herein provides a molecular basis for the terpenoid biosynthesis in this local herb that could be exploited for valuable production using metabolic engineering in both microbial and plant systems.

Methyl jasmonate-induced compositional changes of volatile organic compounds in Polygonum minus leaves

Polygonum minus Huds. is a medicinal aromatic plant rich in terpenes, aldehydes, and phenolic compounds. Methyl jasmonate (MeJA) is a plant signaling molecule commonly applied to elicit stress responses to produce plant secondary metabolites. In this study, the effects of exogenous MeJA treatment on the composition of volatile organic compounds (VOCs) in P. minus leaves were investigated by using a metabolomic approach. Time-course changes in the leaf composition of VOCs on days 1, 3, and 5 after MeJA treatment were analyzed through solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). The VOCs found in MeJA-elicited leaves were similar to those found in mock-treated leaves but varied in quantity at different time points. We focused our analysis on the content and composition of monoterpenes, sesquiterpenes, and green leaf volatiles (GLVs) within the leaf samples. Our results suggest that MeJA enhances the activity of biosynthetic pathways for aldehydes and terpenes in P. minus. Hence, the production of aromatic compounds in this medicinal herb can be increased by MeJA elicitation. Furthermore, the relationship between MeJA elicitation and terpene biosynthesis in P. minus was shown through SPME-GC-MS analysis of VOCs combined with transcriptomic analysis of MeJA-elicited P. minus leaves from our previous study.