Two CYP716A subfamily cytochrome P450 monooxygenases of sweet basil play similar but nonredundant roles in ursane- and oleanane-type pentacyclic triterpene biosynthesis

Unraveling the role of cytochrome P450 enzymes in oleanane triterpenoid biosynthesis in arjuna tree

Triterpenoids (C30-isoprenoids) represent a major group of natural products with various physiological functions in plants. Triterpenoids and their derivatives have medicinal uses owing to diverse bioactivities. Arjuna (Terminalia arjuna) tree bark accumulates highly oxygenated β-amyrin-derived oleanane triterpenoids (e.g., arjunic acid, arjungenin, and arjunolic acid) with cardioprotective roles. However, biosynthetic routes and enzymes remain poorly understood. We mined the arjuna transcriptome and conducted cytochrome P450 monooxygenase (P450) assays using Saccharomyces cerevisiae and Nicotiana benthamiana to identify six P450s and two P450 reductases for oxidative modifications of oleanane triterpenoids. P450 assays using oleananes revealed a greater substrate promiscuity of C-2α and C-23 hydroxylases/oxidases than C-28 oxidases. CYP716A233 and CYP716A432 catalyzed β-amyrin/erythrodiol C-28 oxidation to produce oleanolic acid. C-2α hydroxylases (CYP716C88 and CYP716C89) converted oleanolic acid and hederagenin to maslinic acid and arjunolic acid. CYP716C89 also hydroxylated erythrodiol and oleanolic aldehyde. However, CYP714E107a and CYP714E107b catalyzed oleanolic acid/maslinic acid/arjunic acid, C-23 hydroxylation to form hederagenin, arjunolic acid and arjungenin, and hederagenin C-23 oxidation to produce gypsogenic acid, but at a lower rate than oleanolic acid C-23 hydroxylation. Overall, P450 substrate selectivity suggested that C-28 oxidation is the first P450-catalyzed oxidative modification in the arjuna triterpenoid pathway. However, the pathway might branch thereafter through C-2α/C-23 hydroxylation of oleanolic acid. Taken together, these results provided new insights into substrate range of P450s and unraveled biosynthetic routes of triterpenoids in arjuna. Moreover, complete elucidation and reconstruction of arjunolic acid pathway in S. cerevisiae and N. benthamiana suggested the utility of arjuna P450s in heterologous production of cardioprotective compounds.

Genome-Wide Identification of the CYP716 Gene Family in Platycodon grandiflorus (Jacq.) A. DC. and Its Role in the Regulation of Triterpenoid Saponin Biosynthesis

The main type of saponins occurring in the root of Platycodon grandiflorus (Jacq.) A. DC. are oleanolic acid glycosides. The CYP716 gene family plays a major role in catalyzing the conversion of β-amyrin into oleanolic acid. However, studies on the CYP716 genes in P. grandiflorus are limited, and its evolutionary history remains poorly understood. In this study, 22 PgCYP716 genes were identified, distributed among seven subfamilies. Cis-acting elements of the PgCYP716 promoters were mainly involved in plant hormone regulation and responses to abiotic stresses. PgCYP716A264, PgCYP716A391, PgCYP716A291, and PgCYP716BWv3 genes were upregulated in the root and during saponin accumulation, as shown by RNA-seq analysis, suggesting that these four genes play an important role in saponin synthesis. The results of subcellular localization indicated that these four genes encoded membrane proteins. Furthermore, the catalytic activity of these four genes was proved in the yeast, which catalyzed the conversion of β-amyrin into oleanolic acid. We found that the content of β-amyrin, platycodin D, platycoside E, platycodin D3, and total saponins increased significantly when either of the four genes was over expressed in the transgenic hair root. In addition, the expression of PgSS, PgGPPS2, PgHMGS, and PgSE was also upregulated while these four genes were overexpressed. These data support that these four PgCYP716 enzymes oxidize β-amyrin to produce oleanolic acid, ultimately promoting saponin accumulation by activating the expression of upstream pathway genes. Our results enhanced the understanding of the functional variation among the PgCYP716 gene family involved in triterpenoid biosynthesis and provided a theoretical foundation for improving saponin content and enriching the saponin biosynthetic pathway in P. grandiflorus.

Chromosome-level genome assembly of Prunella vulgaris L. provides insights into pentacyclic triterpenoid biosynthesis

Prunella vulgaris is one of the bestselling and widely used medicinal herbs. It is recorded as an ace medicine for cleansing and protecting the liver in Chinese Pharmacopoeia and has been used as the main constitutions of many herbal tea formulas in China for centuries. It is also a traditional folk medicine in Europe and other countries of Asia. Pentacyclic triterpenoids are a major class of bioactive compounds produced in P. vulgaris. However, their biosynthetic mechanism remains to be elucidated. Here, we report a chromosome-level reference genome of P. vulgaris using an approach combining Illumina, ONT, and Hi-C technologies. It is 671.95 Mb in size with a scaffold N50 of 49.10 Mb and a complete BUSCO of 98.45%. About 98.31% of the sequence was anchored into 14 pseudochromosomes. Comparative genome analysis revealed a recent WGD in P. vulgaris. Genome-wide analysis identified 35 932 protein-coding genes (PCGs), of which 59 encode enzymes involved in 2,3-oxidosqualene biosynthesis. In addition, 10 PvOSC, 358 PvCYP, and 177 PvUGT genes were identified, of which five PvOSCs, 25 PvCYPs, and 9 PvUGTs were predicted to be involved in the biosynthesis of pentacyclic triterpenoids. Biochemical activity assay of PvOSC2, PvOSC4, and PvOSC6 recombinant proteins showed that they were mixed amyrin synthase (MAS), lupeol synthase (LUS), and β-amyrin synthase (BAS), respectively. The results provide a solid foundation for further elucidating the biosynthetic mechanism of pentacyclic triterpenoids in P. vulgaris.

Genome-wide identification and expression analyses of CYP450 genes in sweet potato (Ipomoea batatas L.)

BACKGROUND

Cytochrome P450 monooxygenases (CYP450s) play a crucial role in various biochemical reactions involved in the synthesis of antioxidants, pigments, structural polymers, and defense-related compounds in plants. As sweet potato (Ipomoea batatas L.) holds significant economic importance, a comprehensive analysis of CYP450 genes in this plant species can offer valuable insights into the evolutionary relationships and functional characteristics of these genes.

RESULTS

In this study, we successfully identified and categorized 95 CYP450 genes from the sweet potato genome into 5 families and 31 subfamilies. The predicted subcellular localization results indicate that CYP450s are distributed in the cell membrane system. The promoter region of the IbCYP450 genes contains various cis-acting elements related to plant hormones and stress responses. In addition, ten conserved motifs (Motif1-Motif10) have been identified in the IbCYP450 family proteins, with 5 genes lacking introns and only one exon. We observed extensive duplication events within the CYP450 gene family, which may account for its expansion. The gene duplication analysis results showed the presence of 15 pairs of genes with tandem repeats. Interaction network analysis reveals that IbCYP450 families can interact with multiple target genes and there are protein-protein interactions within the family. Transcription factor interaction analysis suggests that IbCYP450 families interact with multiple transcription factors. Furthermore, gene expression analysis revealed tissue-specific expression patterns of CYP450 genes in sweet potatoes, as well as their response to abiotic stress and plant hormones. Notably, quantitative real-time polymerase chain reaction (qRT‒PCR) analysis indicated the involvement of CYP450 genes in the defense response against nonbiological stresses in sweet potatoes.

CONCLUSIONS

These findings provide a foundation for further investigations aiming to elucidate the biological functions of CYP450 genes in sweet potatoes.

Unraveling the terpene synthase family and characterization of BsTPS2 contributing to (S)-( +)-linalool biosynthesis in Boswellia

Boswellia tree bark exudes oleo-gum resin in response to wounding, which is rich in terpene volatiles. But, the molecular and biochemical basis of wound-induced formation of resin volatiles remains poorly understood. Here, we combined RNA-sequencing (RNA-seq) and metabolite analysis to unravel the terpene synthase (TPS) family contributing to wound-induced biosynthesis of resin volatiles in B. serrata, an economically-important Boswellia species. The analysis of large-scale RNA-seq data of bark and leaf samples representing more than 600 million sequencing reads led to the identification of 32 TPSs, which were classified based on phylogenetic relationship into various TPSs families found in angiosperm species such as TPS-a, b, c, e/f, and g. Moreover, RNA-seq analysis of bark samples collected at 0-24 h post-wounding shortlisted 14 BsTPSs that showed wound-induced transcriptional upregulation in bark, suggesting their important role in wound-induced biosynthesis of resin volatiles. Biochemical characterization of a bark preferentially-expressed and wound-inducible TPS (BsTPS2) in vitro and in planta assays revealed its involvement in resin terpene biosynthesis. Bacterially-expressed recombinant BsTPS2 catalyzed the conversion of GPP and FPP into (S)-( +)-linalool and (E)-(-)-nerolidol, respectively, in vitro assays. However, BsTPS2 expression in Nicotiana benthamiana found that BsTPS2 is a plastidial linalool synthase. In contrast, cytosolic expression of BsTPS2 did not form any product. Overall, the present work unraveled a suite of TPSs that potentially contributed to the biosynthesis of resin volatiles in Boswellia and biochemically characterized BsTPS2, which is involved in wound-induced biosynthesis of (S)-( +)-linalool, a monoterpene resin volatile with a known role in plant defense.

Recent advances in triterpenoid pathway elucidation and engineering

Triterpenoids are among the most assorted class of specialized metabolites found in all the taxa of living organisms. Triterpenoids are the leading active ingredients sourced from plant species and are utilized in pharmaceutical and cosmetic industries. The triterpenoid precursor 2,3-oxidosqualene, which is biosynthesized via the mevalonate (MVA) pathway is structurally diversified by the oxidosqualene cyclases (OSCs) and other scaffold-decorating enzymes such as cytochrome P450 monooxygenases (P450s), UDP-glycosyltransferases (UGTs) and acyltransferases (ATs). A majority of the bioactive triterpenoids are harvested from the native hosts using the traditional methods of extraction and occasionally semi-synthesized. These methods of supply are time-consuming and do not often align with sustainability goals. Recent advancements in metabolic engineering and synthetic biology have shown prospects for the green routes of triterpenoid pathway reconstruction in heterologous hosts such as Escherichia coli, Saccharomyces cerevisiae and Nicotiana benthamiana, which appear to be quite promising and might lead to the development of alternative source of triterpenoids. The present review describes the biotechnological strategies used to elucidate complex biosynthetic pathways and to understand their regulation and also discusses how the advances in triterpenoid pathway engineering might aid in the scale-up of triterpenoid production in engineered hosts.

Characterization of the horse chestnut genome reveals the evolution of aescin and aesculin biosynthesis

Horse chestnut (Aesculus chinensis) is an important medicinal tree that contains various bioactive compounds, such as aescin, barrigenol-type triterpenoid saponins (BAT), and aesculin, a glycosylated coumarin. Herein, we report a 470.02 Mb genome assembly and characterize an Aesculus-specific whole-genome duplication event, which leads to the formation and duplication of two triterpenoid biosynthesis-related gene clusters (BGCs). We also show that AcOCS6, AcCYP716A278, AcCYP716A275, and AcCSL1 genes within these two BGCs along with a seed-specific expressed AcBAHD6 are responsible for the formation of aescin. Furthermore, we identify seven Aesculus-originated coumarin glycoside biosynthetic genes and achieve the de novo synthesis of aesculin in E. coli. Collinearity analysis shows that the collinear BGC segments can be traced back to early-diverging angiosperms, and the essential gene-encoding enzymes necessary for BAT biosynthesis are recruited before the splitting of Aesculus, Acer, and Xanthoceras. These findings provide insight on the evolution of gene clusters associated with medicinal tree metabolites.

The cytochrome P450 gene, MdCYP716B1, is involved in regulating plant growth and anthracnose resistance in apple

Apple is one of the main cultivated fruit trees worldwide. Both biotic and abiotic stresses, especially fungal diseases, have serious effects on the growth and fruit quality of apples. Cytochrome P450, the largest protein family in plants, is critical for plant growth and stress responses. However, the function of apple P450 remains poorly understood. In our previous study, 'Hanfu' autotetraploid showed dwarfism and fungal resistance phenotypes compared to 'Hanfu' diploid. Digital gene expression sequencing analysis revealed that the transcript level of MdCYP716B1 was significantly downregulated in the autotetraploid apple cultivar 'Hanfu'. In this study, we identified and cloned the MdCYP716B1 gene from 'Hanfu' apples. The MdCYP716B1 protein fused to a green fluorescent protein was localized in the cytoplasm. We constructed the plant overexpression vector and RNAi vector of MdCYP716B1, and the apple 'GL-3' was transformed by Agrobacterium-mediated transformation to obtain transgenic plants. Overexpressing and RNAi silencing transgenic plants exhibited an increase and decrease in plant height to 'GL-3', respectively. RNAi silencing transgenic plants displayed increased resistance to Colletotrichum gloeosporioides, whereas overexpression transgenic plants were more sensitive to C. gloeosporioides. According to transcriptome analysis, the transcript levels of gibberellin biosynthesis genes were upregulated in MdCYP716B1-overexpression plants. In contrast with 'GL-3', GA3 accumulation was rose in MdCYP716B1-OE lines and impaired in MdCYP716B1-RNAi lines. Collectively, our data indicate that MdCYP716B1 regulates plant growth and resistance to fungal stress.

Natural products of pentacyclic triterpenoids: from discovery to heterologous biosynthesis

Covering: up to 2022Pentacyclic triterpenoids are important natural bioactive substances that are widely present in plants and fungi. They have significant medicinal efficacy, play an important role in reducing blood glucose and protecting the liver, and have anti-inflammatory, anti-oxidation, anti-fatigue, anti-viral, and anti-cancer activities. Pentacyclic triterpenoids are derived from the isoprenoid biosynthetic pathway, which generates common precursors of triterpenes and steroids, followed by cyclization with oxidosqualene cyclases (OSCs) and decoration via cytochrome P450 monooxygenases (CYP450s) and glycosyltransferases (GTs). Many biosynthetic pathways of triterpenoid saponins have been elucidated by studying their metabolic regulation network through the use of multiomics and identifying their functional genes. Unfortunately, natural resources of pentacyclic triterpenoids are limited due to their low content in plant tissues and the long growth cycle of plants. Based on the understanding of their biosynthetic pathway and transcriptional regulation, plant bioreactors and microbial cell factories are emerging as alternative means for the synthesis of desired triterpenoid saponins. The rapid development of synthetic biology, metabolic engineering, and fermentation technology has broadened channels for the accumulation of pentacyclic triterpenoid saponins. In this review, we summarize the classification, distribution, structural characteristics, and bioactivity of pentacyclic triterpenoids. We further discuss the biosynthetic pathways of pentacyclic triterpenoids and involved transcriptional regulation. Moreover, the recent progress and characteristics of heterologous biosynthesis in plants and microbial cell factories are discussed comparatively. Finally, we propose potential strategies to improve the accumulation of triterpenoid saponins, thereby providing a guide for their future biomanufacturing.

Hydroxylases involved in terpenoid biosynthesis: a review

Terpenoids are pervasive in nature and display an immense structural diversity. As the largest category of plant secondary metabolites, terpenoids have important socioeconomic value in the fields of pharmaceuticals, spices, and food manufacturing. The biosynthesis of terpenoid skeletons has made great progress, but the subsequent modifications of the terpenoid framework are poorly understood, especially for the functionalization of inert carbon skeleton usually catalyzed by hydroxylases. Hydroxylase is a class of enzymes that plays an important role in the modification of terpenoid backbone. This review article outlines the research progress in the identification, molecular modification, and functional expression of this class of enzymes in the past decade, which are profitable for the discovery, engineering, and application of more hydroxylases involved in the plant secondary metabolism.

Genome-wide investigation of Cytochrome P450 superfamily of Aquilaria agallocha: Association with terpenoids and phenylpropanoids biosynthesis

Agarwood is a dark resinous wood, produced when Aquilaria tree responds to wounding and microbial infection resulting in the accumulation of fragrant metabolites. Sesquiterpenoids and 2-(2-phenylethyl) chromones are the major phytochemicals in agarwood and Cytochrome P450s (CYPs) are one of the important enzymes in the biosynthesis of these fragrant chemicals. Thus, understanding the repertoire of CYP superfamily in Aquilaria can not only give insights into the fundamentals of agarwood formation, but can also provide a tool for the overproduction of the aroma chemicals. Therefore, current study was designed to investigate CYPs of an agarwood producing plant, Aquilaria agallocha. We identified 136 CYP genes from A. agallocha genome (AaCYPs) and classified them into 8 clans and 38 families. The promoter regions had stress and hormone-related cis-regulatory elements which indicate their participation in the stress response. Duplication and synteny analysis revealed segmental and tandem duplicated and evolutionary related CYP members in other plants. Potential members involved in the biosynthesis of sesquiterpenoids and phenylpropanoids were identified and found to be upregulated in methyl jasmonate-induced callus and infected Aquilaria trees by real-time quantitative PCR analyses. This study highlights the possible involvement of AaCYPs in agarwood resin development and their complex regulation during stress exposure.

In vivo characterization of key iridoid biosynthesis pathway genes in catnip (Nepeta cataria)

Using virus-induced gene silencing, we demonstrated that the enzymes GES, ISY, and MLPL are responsible for nepetalactone biosynthesis in Nepeta cataria. Nepetalactone is the main iridoid that is found in the Nepeta genus and is well-known for its psychoactive effect on house cats. Moreover, there is a burgeoning interest into the effect of nepetalactone on insects. Although the enzymes for nepetalactone biosynthesis have been biochemically assayed in vitro, validation of the role that these enzymes have in planta has not been demonstrated. Virus-induced gene silencing (VIGS) is a silencing method that relies on transient transformation and is an approach that has been particularly successful when applied to a variety of non-model plants. Here, we use a recently designed visual-marker dependent VIGS system to demonstrate that the nepetalactone biosynthetic enzymes GES, ISY, and MLPL impact nepetalactone biosynthesis in Nepeta cataria.

Betulin, Synthesized by PpCYP716A1, Is a Key Endogenous Defensive Metabolite of Peach against Aphids

Wild pest-resistant germplasms employ secondary metabolites to withstand insect attacks. A close wild relative of the cultivated peach, Prunus davidiana, displays strong resistance to green peach aphids by utilizing metabolites to cope with aphid infestation; however, the underlying mechanism of aphid resistance remains mostly unknown. Here, metabolomic analysis was performed to explore the changes in metabolite levels in P. davidiana after aphid infestation. The data revealed that betulin is a key defensive metabolite in peaches that protects against aphids and possesses potent aphidicidal activity. Further toxicity tests demonstrated that betulin was toxic to pests but not to beneficial insects. Additionally, transcriptomic and phylogenetic analyses revealed that the cytochrome P450 gene PpCYP716A1 was responsible for betulin synthesis─this finding was confirmed by the heterologous expression of this gene. This study revealed a strategy whereby plants harness defense metabolites to develop resistance to pests. These findings may facilitate controlling such pests.

Cytochrome P450 monooxygenase-mediated tailoring of triterpenoids and steroids in plants

The cytochrome P450 monooxygenase (CYP) superfamily comprises hemethiolate enzymes that perform remarkable regio- and stereospecific oxidative chemistry. As such, CYPs are key agents for the structural and functional tailoring of triterpenoids, one of the largest classes of plant natural products with widespread applications in pharmaceuticals, food, cosmetics, and agricultural industries. In this review, we provide a full overview of 149 functionally characterised CYPs involved in the biosynthesis of triterpenoids and steroids in primary as well as in specialised metabolism. We describe the phylogenetic distribution of triterpenoid- and steroid-modifying CYPs across the plant CYPome, present a structure-based summary of their reactions, and highlight recent examples of particular interest to the field. Our review therefore provides a comprehensive up-to-date picture of CYPs involved in the biosynthesis of triterpenoids and steroids in plants as a starting point for future research.

Advances in production and structural derivatization of the promising molecule ursolic acid

Ursolic acid (UA) is a ursane-type pentacyclic triterpenoid compound, naturally produced in plants via specialized metabolism and exhibits vast range of remarkable physiological activities and pharmacological manifestations. Owing to significant safety and efficacy in different medical conditions, UA may serve as a backbone to produce its derivatives with novel therapeutic functions. This review aims to provide ideas for exploring more diverse structures to improve UA pharmacological activity and increasing its biological yield to meet the industrial requirements by systematically reviewing the current research progress of UA. We first provides an overview of the pharmacological activities, acquisition methods and structural modifications of UA. Among them, we focused on the synthetic modifications of UA to yield valuable derivatives with enhanced therapeutic potential. Furthermore, harnessing the essential advances for green synthesis of UA and its derivatives by advent of metabolic engineering and synthetic biology are of great concern. In this regard, all pivotal advances for enhancing the production of UA have been discussed. In combination with the advantages of UA biosynthesis and transformation strategy, large-scale microbial production of UA is a promising platform for further exploration.

Relationship between Maturity Stage, Triterpenoid Content and Cytotoxicity of Sorbus intermedia (EHRH.) PERS. Fruits - A Chemometric Approach

In this study, two ursane-type triterpenes, i. e., ursolic acid (UA) and 3-O-β-acetoxyursolic acid (AUA), were isolated and quantified in Sorbus intermedia (EHRH.) PERS. fruits. UA and AUA levels differed slightly throughout fruit maturation, and both triterpenes showed similar dynamics of accumulation with the highest levels found in ripe fruits (up to 6.33±0.56 and 1.17±0.18 mg/g dw. of UA and AUA, respectively). The extracts derived from unripe fruits displayed significant cytotoxic effects against WM793, DU-145, PC3, 8505C, Caco2 and A549 cells, but no correlation between UA and AUA levels and cytotoxicity was found. On the other hand, extracts from mature fruits were not active towards almost all of the tested cell lines. The chemometric approach showed that the extracts derived from fruits harvested earlier clustered to form a clearly distanced group from extracts prepared from more-mature fruits. The extracts at higher concentrations formed separate groups, which indicated the concentration-dependent effect of these extracts on the cells.

BAHD acetyltransferase contributes to wound-induced biosynthesis of oleo-gum resin triterpenes in Boswellia

Triterpenes (30-carbon isoprene compounds) represent a large and highly diverse class of natural products that play various physiological functions in plants. The triterpene biosynthetic enzymes, particularly those catalyzing the late-stage regio-selective modifications are not well characterized. The bark of select Boswellia trees, e.g., B. serrata exudes specialized oleo-gum resin in response to wounding, which is enriched with boswellic acids (BAs), a unique class of C3α-epimeric pentacyclic triterpenes with medicinal properties. The bark possesses a network of resin secretory structures comprised of vertical and horizontal resin canals, and amount of BAs in bark increases considerably in response to wounding. To investigate BA biosynthetic enzymes, we conducted tissue-specific transcriptome profiling and identified a wound-responsive BAHD acetyltransferase (BsAT1) of B. serrata catalyzing the late-stage C3α-O-acetylation reactions in the BA biosynthetic pathway. BsAT1 catalyzed C3α-O-acetylation of αBA, βBA, and 11-keto-βBA in vitro and in planta assays to produce all the major C3α-O-acetyl-BAs (3-acetyl-αBA, 3-acetyl-βBA, and 3-acetyl-11-keto-βBA) found in B. serrata bark and oleo-gum resin. BsAT1 showed strict specificity for BA scaffold, whereas it did not acetylate the more common C3β-epimeric pentacyclic triterpenes. The analysis of steady-state kinetics using various BAs revealed distinct substrate affinity and catalytic efficiency. BsAT1 transcript expression coincides with increased levels of C3α-O-acetyl-BAs in bark in response to wounding, suggesting a role of BsAT1 in wound-induced biosynthesis of C3α-O-acetyl-BAs. Overall, the results provide new insights into the biosynthesis of principal chemical constituents of Boswellia oleo-gum resin.

Application of virus-induced gene silencing in Andrographis paniculata, an economically important medicinal plant

Kalmegh [Andrographis paniculata (Burm.f.) Wall. ex Nees] is one of the most studied medicinal plants for pharmaceutical properties and phytochemistry. However, functional genomics studies in kalmegh are so far limited due to the unavailability of a robust tool for gene silencing. Here, we tested the application of virus-induced gene silencing (VIGS) in kalmegh using the well-known Tobacco rattle virus (TRV)-based vectors and achieved targeted silencing of phytoene desaturase (ApPDS) which is essential in plants for carotenoid biosynthesis that protects chlorophyll from photooxidation. ApPDS silencing in kalmegh leaves developed a typical photobleaching phenotype. The silencing of ApPDS was confirmed by analysing ApPDS transcript level and determining chlorophyll content in the leaves of VIGS seedlings. The analysis revealed ~30% reduction in chlorophyll content, and 40 to 60% reduction in ApPDS transcript level in the leaves of VIGS seedlings. These findings clearly demonstrated the applicability of VIGS in kalmegh using TRV-based vectors. The VIGS protocol presented in this study might be useful for studying gene function related to medicinal and agricultural traits in kalmegh.

UGT86C11 is a novel plant UDP-glycosyltransferase involved in labdane diterpene biosynthesis

Glycosyltransferases constitute a large family of enzymes across all domains of life, but knowledge of their biochemical function remains largely incomplete, particularly in the context of plant specialized metabolism. The labdane diterpenes represent a large class of phytochemicals with many pharmacological benefits, such as anti-inflammatory, hepatoprotective, and anticarcinogenic. The medicinal plant kalmegh (Andrographis paniculata) produces bioactive labdane diterpenes; notably, the C19-hydroxyl diterpene (andrograpanin) is predominantly found as C19-O-glucoside (neoandrographolide), whereas diterpenes having additional hydroxylation(s) at C3 (14-deoxy-11,12-didehydroandrographolide) or C3 and C14 (andrographolide) are primarily detected as aglycones, signifying scaffold-selective C19-O-glucosylation of diterpenes in planta. Here, we analyzed UDP-glycosyltransferase (UGT) activity and diterpene levels across various developmental stages and tissues and found an apparent correlation of UGT activity with the spatiotemporal accumulation of neoandrographolide, the major diterpene C19-O-glucoside. The biochemical analysis of recombinant UGTs preferentially expressed in neoandrographolide-accumulating tissues identified a previously uncharacterized UGT86 member (ApUGT12/UGT86C11) that catalyzes C19-O-glucosylation of diterpenes with strict scaffold selectivity. ApUGT12 localized to the cytoplasm and catalyzed diterpene C19-O-glucosylation in planta. The substrate selectivity demonstrated by the recombinant ApUGT12 expressed in plant and bacterium hosts was comparable to native UGT activity. Recombinant ApUGT12 showed significantly higher catalytic efficiency using andrograpanin compared with 14-deoxy-11,12-didehydroandrographolide and trivial activity using andrographolide. Moreover, ApUGT12 silencing in plants led to a drastic reduction in neoandrographolide content and increased levels of andrograpanin. These data suggest the involvement of ApUGT12 in scaffold-selective C19-O-glucosylation of labdane diterpenes in plants. This knowledge of UGT86 function might help in developing plant chemotypes and synthesis of pharmacologically relevant diterpenes.

Methyl jasmonate enhances ursolic, oleanolic and rosmarinic acid production and sucrose induced biomass accumulation, in hairy roots of Lepechinia caulescens

Background

Ursolic (UA), oleanolic (OA) and rosmarinic (RA) acids are bioactive metabolites found in Lepechinia caulescens that have generated interest for their health benefits, which include antimicrobial, antioxidant, antimutagenic, gastroprotective, antidiabetic, antihypertensive and anti-inflammatory properties, among others. To date, very few attempts have been made to evaluate the potential for simultaneous production of these bioactive compounds, using a biotechnological approach. Hairy root cultures offer a biotechnology approach that can be used to study the factors affecting the biosynthesis and the production of UA, OA and RA. In the current study, we established hairy root cultures of L. caulescens and evaluated the effect of sucrose on biomass accumulation, and the effect of different concentrations and times of exposure of methyl jasmonate (MeJA), on the accumulation of UA, OA and RA.

Methods

Leaves from plants of L. caulescens were inoculated with Agrobacterium rhizogenes strain ATCC 15834. PCR of rolB gene confirmed the transgenic nature of hairy roots. Hairy roots were subcultured in semisolid MSB5 medium, supplemented with 15, 30, 45 or 60 g/L sucrose and after 4 weeks, dry weight was determined. The accumulation of UA, OA and RA of wild plants and hairy roots were determined by HPLC. Finally, the hairy roots were treated with 0, 100, 200 and 300 µM of MeJA and the content of bioactive compounds was analyzed, after 24, 48 and 72 h.

Results

High frequency transformation (75%) was achieved, using leaf explants from axenic seedlings, infected with A. rhizogenes. The hairy roots showed an enhanced linear biomass accumulation, in response to the increase in sucrose concentration. The hairy root cultures in MSB5 medium, supplemented with 45 g/L sucrose, were capable to synthesizing UA (0.29 ± 0.00 mg/g DW), OA (0.57 ± 0.00 mg/g DW) and RA (41.66 ± 0.31 mg/g DW), about two, seven and three times more, respectively, than in roots from wild plants. Elicitation time and concentration of MeJA resulted in significant enhancement in the production of UA, OA and RA, with treatments elicited for 24 h, with a concentration of 300 µM of MeJA, exhibiting greatest accumulation.

Conclusion

This is the first report on development of hairy root cultures of L. caulescens. Future studies should aim towards further improving triterpenes and polyphenolic compound production in hairy roots of L. caulescens, for use in the pharmaceutical and biotechnological industry.

Virus-Induced Gene Silencing in Nepeta

Virus-induced gene silencing (VIGS) is a versatile tool for genetic studies that has been applied to a variety of plant species. With the advent of more accessible genomic and transcriptomic technology applied to an increasing range of plants, tools such as VIGS are being adapted to more non-model plants to explore genes relevant to agriculture and chemical discovery. In this protocol, we adapted VIGS technology to target genes in Nepeta cataria (catnip) and Nepeta mussinii (catmint). These plants carry biochemical and economical value for their production of nepetalactone, an iridoid which provokes a strong reaction in both house cats and aphids. We describe a method to target magnesium chelatase subunit H (CHlH), a gene often targeted as a visual marker for VIGS. Furthermore, we describe a method to simultaneously target two genes in a single plant, which aids in the study of genes found in key biochemical steps in the production of nepetalactone. This approach, which was successfully applied in two members of the Lamiaceae family (mint), could be adapted to other members of the mint family with economical and chemical value.

Endophytes, biotransforming microorganisms, and engineering microbial factories for triterpenoid saponins production

Triterpenoid saponins are structurally diverse secondary metabolites. They are the main active ingredient of many medicinal plants and have a wide range of pharmacological effects. Traditional production of triterpenoid saponins, directly extracted from cultivated plants, cannot meet the rapidly growing demand of pharmaceutical industry. Microorganisms with triterpenoid saponins production ability (especially Agrobacterium genus) and biotransformation ability, such as fungal species in Armillaria and Aspergillus genera and bacterial species in Bacillus and Intestinal microflora, represent a valuable source of active metabolites. With the development of synthetic biology, engineering microorganisms acquired more potential in terms of triterpenoid saponins production. This review focusses on potential mechanisms and the high yield strategies of microorganisms with inherent production or biotransformation ability of triterpenoid saponins. Advances in the engineering of microorganisms, such as Saccharomyces cerevisiae, Yarrowia lipolytica, and Escherichia coli, for the biosynthesis triterpenoid saponins de novo have also been reported. Strategies to increase the yield of triterpenoid saponins in engineering microorganisms are summarized following four aspects, that is, introduction of high efficient gene, optimization of enzyme activity, enhancement of metabolic flux to target compounds, and optimization of fermentation conditions. Furthermore, the challenges and future directions for improving the yield of triterpenoid saponins biosynthesis in engineering microorganisms are discussed.

Comparative Analysis of NADPH-Cytochrome P450 Reductases From Legumes for Heterologous Production of Triterpenoids in Transgenic Saccharomyces cerevisiae

Triterpenoids are plant specialized metabolites with various pharmacological activities. They are widely distributed in higher plants, such as legumes. Because of their low accumulation in plants, there is a need for improving triterpenoid production. Cytochrome P450 monooxygenases (CYPs) play critical roles in the structural diversification of triterpenoids. To perform site-specific oxidations, CYPs require the electrons that are transferred by NADPH-cytochrome P450 reductase (CPR). Plants possess two main CPR classes, class I and class II. CPR classes I and II have been reported to be responsible for primary and specialized (secondary) metabolism, respectively. In this study, we first analyzed the CPR expression level of three legumes species, Medicago truncatula, Lotus japonicus, and Glycyrrhiza uralensis, showing that the expression level of CPR class I was lower and more stable, while that of CPR class II was higher in almost all the samples. We then co-expressed different combinations of CYP716As and CYP72As with different CPR classes from these three legumes in transgenic yeast. We found that CYP716As worked better with CPR-I from the same species, while CYP72As worked better with any CPR-IIs. Using engineered yeast strains, CYP88D6 paired with class II GuCPR produced the highest level of 11-oxo-β-amyrin, the important precursor of high-value metabolites glycyrrhizin. This study provides insight into co-expressing genes from legumes for heterologous production of triterpenoids in yeast.

Biosynthesis, total synthesis, structural modifications, bioactivity, and mechanism of action of the quinone-methide triterpenoid celastrol

Celastrol, a quinone-methide triterpenoid, was extracted from Tripterygium wilfordii Hook. F. in 1936 for the first time. Almost 70 years later, it is considered one of the molecules most likely to be developed into modern drugs, as it exhibits notable bioactivity, including anticancer and anti-inflammatory activity, and exerts antiobesity effects. In addition, the molecular mechanisms underlying its bioactivity are being widely studied, which offers new avenues for its development as a pharmaceutical reagent. Owing to its potential therapeutic effects and unique chemical structure, celastrol has attracted considerable interest in the fields of organic, biosynthesis, and medicinal chemistry. As several steps in the biosynthesis of celastrol have been revealed, the mechanisms of key enzymes catalyzing the formation and postmodifications of the celastrol scaffold have been gradually elucidated, which lays a good foundation for the future heterogeneous biosynthesis of celastrol. Chemical synthesis is also an effective approach to obtain celastrol. The total synthesis of celastrol was realized for the first time in 2015, which established a new strategy to obtain celastroid natural products. However, owing to the toxic effects and suboptimal pharmacological properties of celastrol, its clinical applications remain limited. To search for drug-like derivatives, several structurally modified compounds were synthesized and tested. This review focuses primarily on the latest research progress in the biosynthesis, total synthesis, structural modifications, bioactivity, and mechanism of action of celastrol. We anticipate that this paper will facilitate a more comprehensive understanding of this promising compound and provide constructive references for future research in this field.

Advances in biosynthesis of triterpenoid saponins in medicinal plants

In recent years, biosynthesis of triterpenoid saponins in medicinal plants has been widely studied because of their active ingredients with diverse pharmacological activities. Various oxidosqualene cyclases, cytochrome P450 monooxygenases, uridine diphosphate glucuronosyltransferases, and transcription factors related to triterpenoid saponins biosynthesis have been explored and identified. In the biosynthesis of triterpenoid saponins, the progress of gene mining by omics-based sequencing, gene screening, gene function verification, catalyzing mechanism of key enzymes and gene regulation are summarized and discussed. By the progress of the biosynthesis pathway of triterpenoid saponins, the large-scale production of some triterpenoid saponins and aglycones has been achieved through plant tissue culture, transgenic plants and engineered yeast cells. However, the complex biosynthetic pathway and structural diversity limit the biosynthesis of triterpenoid saponins in different system. Special focus can further be placed on the systematic botany information of medicinal plants obtained from omics large dataset, and triterpenoid saponins produced by synthetic biology strategies, gene mutations and gene editing technology.

Ursolic acid protects against cisplatin‑induced ototoxicity by inhibiting oxidative stress and TRPV1‑mediated Ca2+‑signaling

Cisplatin (CDDP) is widely used in clinical settings for the treatment of various cancers. However, ototoxicity is a major side effect of CDDP, and there is an associated risk of irreversible hearing loss. We previously demonstrated that CDDP could induce ototoxicity via activation of the transient receptor potential vanilloid receptor 1 (TRPV1) pathway and subsequent induction of oxidative stress. The present study investigated whether ursolic acid (UA) treatment could protect against CDDP‑induced ototoxicity. UA is a triterpenoid with strong antioxidant activity widely used in China for the treatment of liver diseases. This traditional Chinese medicine is mainly isolated from bearberry, a Chinese herb. The present results showed that CDDP increased auditory brainstem response threshold shifts in frequencies associated with observed damage to the outer hair cells. Moreover, CDDP increased the expression of TRPV1, calpain 2 and caspase‑3 in the cochlea, and the levels of Ca2+ and 4‑hydroxynonenal. UA co‑treatment significantly attenuated CDDP‑induced hearing loss and inhibited TRPV1 pathway activation. In addition, UA enhanced CDDP‑induced growth inhibition in the human ovarian cancer cell line SKOV3, suggesting that UA synergizes with CDDP in vitro. Collectively, the present data suggested that UA could effectively attenuate CDDP‑induced hearing loss by inhibiting the TRPV1/Ca²+/calpain‑oxidative stress pathway without impairing the antitumor effects of CDDP.

Transcriptome analysis and functional characterization of oxidosqualene cyclases of the arjuna triterpene saponin pathway

Arjuna (Terminalia arjuna) tree has been popular in Indian traditional medicine to treat cardiovascular ailments. The tree accumulates bioactive triterpene glycosides (saponins) and aglycones (sapogenins), in a tissue-preferential manner. Oleanane triterpenes/saponins (derived from β-amyrin) with potential cardioprotective function predominantly accumulate in the bark. However, arjuna triterpene saponin pathway enzymes remain to be identified and biochemically characterized. Here, we employed a combined transcriptomics, metabolomics and biochemical approach to functionally define a suite of oxidosqualene cyclases (OSCs) that catalyzed key reactions towards triterpene scaffold diversification. De novo assembly of 131 millions Illumina NextSeq500 sequencing reads obtained from leaf and stem bark samples led to a total of 156,650 reference transcripts. Four distinct OSCs (TaOSC1-4) with 54-71 % sequence identities were identified and functionally characterized. TaOSC1, TaOSC3 and TaOSC4 were biochemically characterized as β-amyrin synthase, cycloartenol synthase and lupeol synthase, respectively. However, TaOSC2 was found to be a multifunctional OSC producing both α-amyrin and β-amyrin, but showed a preference for α-amyrin product. Both TaOSC1 and TaOSC2 produced β-amyrin, the direct precursor for oleanane triterpene/saponin biosynthesis; but, TaOSC1 transcript expressed preferentially in bark, suggesting a major role of TaOSC1 in the biosynthesis of oleanane triterpenes/saponins in bark.

Virus-Induced Gene Silencing in Sweet Basil (Ocimum basilicum)

Virus-induced gene silencing (VIGS) is a powerful reverse genetic tool for rapid functional analysis of plant genes. Over the last decade, VIGS has been widely used for conducting rapid gene knockdown experiment in plants and played a crucial role in advancing applied and basic research in plant science. VIGS was studied extensively in model plants Arabidopsis and tobacco. Moreover, several non-model plants such as Papaver (Hileman et al., Plant J 44:334-341, 2005), Aquilegia (Gould and Kramer, Plant Methods 3:6, 2007), Catharanthus (Liscombe and O'Connor, Phytochemistry 72:1969-1977, 2011), Withania (Singh et al., Plant Biol J 13:1287-1299, 2015), and Ocimum (Misra et al., New Phytol 214:706-720, 2017) were also successfully explored. We have recently developed a robust protocol for VIGS in sweet basil (Ocimum basilicum). Sweet basil, a popular medicinal/aromatic herb, is being studied for the diversity of specialized metabolites produced in it.

Virus-Induced Gene Silencing in Olive Tree (Oleaceae)

Research on gene functions in non-model tree species is hampered by a number of difficulties such as time-consuming genetic transformation protocols and extended period for the production of healthy transformed offspring, among others. Virus-induced gene silencing (VIGS) is an alternative approach to transiently knock out an endogenous gene of interest (GOI) by the introduction of viral sequences encompassing a fragment of the GOI and to exploit the posttranscriptional gene silencing (PTGS) mechanism of the plant, thus triggering silencing of the GOI. Here we describe the successful application of Tobacco rattle virus (TRV)-mediated VIGS through agroinoculation of olive plantlets. This methodology is expected to serve as a fast tracking and powerful tool enabling researchers from diversified fields to perform functional genomic analyses in the olive tree.

Quantitative trait loci influencing pentacyclic triterpene composition in apple fruit peel

The chemical composition of pentacyclic triterpenes was analysed using a ‘Royal Gala’ x ‘Granny Smith’ segregating population in 2013 and 2015, using apple peels extracted from mature fruit at harvest and after 12 weeks of cold storage. In 2013, 20 compound isoforms from nine unique compound classes were measured for both treatments. In 2015, 20 and 17 compound isoforms from eight unique compound classes were measured at harvest and after cold storage, respectively. In total, 68 quantitative trait loci (QTLs) were detected on 13 linkage groups (LG). Thirty two and 36 QTLs were detected for compounds measured at harvest and after cold storage, respectively. The apple chromosomes with the most QTLs were LG3, LG5, LG9 and LG17. The largest effect QTL was for trihydroxy-urs-12-ene-28-oic acid, located on LG5; this was measured in 2015 after storage, and was inherited from the ‘Royal Gala’ parent (24.9% of the phenotypic variation explained).

Lotus japonicus Triterpenoid Profile and Characterization of the CYP716A51 and LjCYP93E1 Genes Involved in Their Biosynthesis In Planta

Lotus japonicus is an important model legume plant in several fields of research, such as secondary (specialized) metabolism and symbiotic nodulation. This plant accumulates triterpenoids; however, less information regarding its composition, content and biosynthesis is available compared with Medicago truncatula and Glycine max. In this study, we analyzed the triterpenoid content and composition of L. japonicus. Lotus japonicus accumulated C-28-oxidized triterpenoids (ursolic, betulinic and oleanolic acids) and soyasapogenols (soyasapogenol B, A and E) in a tissue-dependent manner. We identified an oxidosqualene cyclase (OSC) and two cytochrome P450 enzymes (P450s) involved in triterpenoid biosynthesis using a yeast heterologous expression system. OSC9 was the first enzyme derived from L. japonicus that showed α-amyrin (a precursor of ursolic acid)-producing activity. CYP716A51 showed triterpenoid C-28 oxidation activity. LjCYP93E1 converted β-amyrin into 24-hydroxy-β-amyrin, a metabolic intermediate of soyasapogenols. The involvement of the identified genes in triterpenoid biosynthesis in L. japonicus plants was evaluated by quantitative real-time PCR analysis. Furthermore, gene loss-of-function analysis of CYP716A51 and LjCYP93E1 was conducted. The cyp716a51-mutant L. japonicus hairy roots generated by the genome-editing technique produced no C-28 oxidized triterpenoids. Likewise, the complete abolition of soyasapogenols and soyasaponin I was observed in mutant plants harboring Lotus retrotransposon 1 (LORE1) in LjCYP93E1. These results indicate that the activities of these P450 enzymes are essential for triterpenoid biosynthesis in L. japonicus. This study increases our understanding of triterpenoid biosynthesis in leguminous plants and provides information that will facilitate further studies of the physiological functions of triterpenoids using L. japonicus.

Research advances in cytochrome P450-catalysed pharmaceutical terpenoid biosynthesis in plants

Terpenoids, the biggest class of plant secondary metabolites, have a wide range of significant physiological roles, while many of them are important natural drugs. Biosynthesis of pharmaceutical terpenoids in plants is a fairly complex process, most of which involves cytochrome P450 (CYP450) monooxygenases. CYP450 enzymes are versatile biocatalysts that play critical roles in terpenoid skeleton modification and structural diversity. Therefore, the discovery and identification of CYP450 genes is significant for elucidating the terpenoid biosynthetic pathway. This review summarizes the progress and cloning strategies relating to CYP450s in pharmaceutical terpenoid biosynthesis of the past decade.

The transcriptome enables the identification of candidate genes behind medicinal value of Drumstick tree (Moringa oleifera)

Moringa oleifera is a plant well-known for its nutrition value, drought resistance and medicinal properties. cDNA libraries from five different tissues (leaf, root, stem, seed and flower) of M. oleifera cultivar Bhagya were generated and sequenced. We developed a bioinformatics pipeline to assemble transcriptome, along with the previously published M. oleifera genome, to predict 17,148 gene models. Few candidate genes related to biosynthesis of secondary metabolites, vitamins and ion transporters were identified. Expressions were further confirmed by real-time quantitative PCR experiments for few promising leads. Quantitative estimation of metabolites, as well as elemental analysis, was also carried out to support our observations. Enzymes in the biosynthesis of vitamins and metabolites like quercetin and kaempferol are highly expressed in leaves, flowers and seeds. The expression of iron transporters and calcium storage proteins were observed in root and leaves. In general, leaves retain the highest amount of small molecules of interest.

The enzymes OSC1 and CYP716A263 produce a high variety of triterpenoids in the latex of Taraxacum koksaghyz

Only very little is known about the resin composition of natural rubber from the dandelion species Taraxacum koksaghyz, thus its full characterization could provide new insights into how the isoprenoid end-products influence the physical properties of natural rubber, and this resin might be a good source of highly diverse triterpenoids. Here, we present a comprehensive analysis of the triterpenoid composition in an acetone extract and identified 13 triterpenes and triterpenoids also including the so far unknown pentacyclic compounds lup-19(21)-en-3-ol (1) and its ketone lup-19(21)-en-3-one (2). We purified single triterpenes from the acetone extract by developing a two-step HPLC system that is adapted to the structural differences of the described triterpenoids. Furthermore, we isolated six different oxidosqualene cyclases (OSCs) and two P450 enzymes, and we functionally characterized TkOSC1 and CYP716A263 in Nicotiana benthamiana and Saccharomyces cerevisiae in detail. TkOSC1 is a multifunctional OSC that was capable of synthesizing at least four of the latex-predominant pentacyclic triterpenes (taraxasterol, α-, β-amyrin and lup-19(21)-en-3-ol) while CYP716A263 oxidized pentacyclic triterpenes at the C-3 position. The identified enzymes responsible for biosynthesis and modification of pentacyclic triterpenes in T. koksaghyz latex may represent excellent tools for bioengineering approaches to produce pentacyclic triterpenes heterologously.

Oxidosqualene cyclase and CYP716 enzymes contribute to triterpene structural diversity in the medicinal tree banaba

Pentacyclic triterpenes (PCTs) represent a major class of bioactive metabolites in banaba (Lagerstroemia speciosa) leaves; however, biosynthetic enzymes and their involvement in the temporal accumulation of PCTs remain to be studied. We use an integrated approach involving transcriptomics, metabolomics and gene function analysis to identify oxidosqualene cyclases (OSCs) and cytochrome P450 monooxygenases (P450s) that catalyzed sequential cyclization and oxidative reactions towards PCT scaffold diversification. Four monofunctional OSCs (LsOSC1,3-5) converted the triterpene precursor 2,3-oxidosqualene to either lupeol, β-amyrin or cycloartenol, and a multifunctional LsOSC2 formed α-amyrin as a major product along with β-amyrin. Two CYP716 family P450s (CYP716A265, CYP716A266) catalyzed C-28 oxidation of α-amyrin, β-amyrin and lupeol to form ursolic acid, oleanolic acid and betulinic acid, respectively. However, CYP716C55 catalyzed C-2α hydroxylation of ursolic acid and oleanolic acid to produce corosolic acid and maslinic acid, respectively. Besides, combined transcript and metabolite analysis suggested major roles for the LsOSC2, CYP716A265 and CYP716C55 in determining leaf ursane and oleanane profiles. Combinatorial expression of OSCs and CYP716s in Saccharomyces cerevisiae and Nicotiana benthamiana led to PCT pathway reconstruction, signifying the utility of banaba enzymes for bioactive PCT production in alternate plant/microbial hosts that are more easily tractable than the tree species.

Multi-omics data-driven investigations of metabolic diversity of plant triterpenoids

The vast majority of structurally diverse metabolites play essential roles in mediating the interactions between plant and environment, and constitute a valuable resource for industrial applications. Recent breakthroughs in sequencing technology have greatly accelerated metabolic studies of natural plant products, providing opportunities to investigate the molecular basis underlying the diversity of specialized plant metabolites through large-scale analysis. Here, we focus on the biosynthesis of plant triterpenoids, especially the three diversifying reactions (cyclization, oxidation and glycosylation) that largely contribute to the structural diversity of triterpenoids. Gene mining through large-scale omics data and functional characterization of metabolic genes including enzymes, transcription factors and transporters could provide important insights into the evolution of specialized plant metabolism and pave the way for the production of high-value metabolites or derivatives using synthetic biology approaches.

Comparative analysis of CYP716A subfamily enzymes for the heterologous production of C-28 oxidized triterpenoids in transgenic yeast

Several enzymes of the CYP716A subfamily have been reported to be involved in triterpenoid biosynthesis. Members of this subfamily oxidize various positions along the triterpenoid backbone and the majority of them catalyze a three-step oxidation at the C-28 position. Interestingly, C-28 oxidation is a common feature in oleanolic acid, ursolic acid, and betulinic acid, which are widely distributed in plants and exhibit important biological activities. In this work, three additional CYP716A enzymes isolated from olive, sugar beet, and coffee, were characterized as multifunctional C-28 oxidases. Semi-quantitative comparisons of in vivo catalytic activity were made against the previously characterized enzymes CYP716A12, CYP716A15, and CYP716A52v2. When heterologously expressed in yeast, the isolated enzymes differed in both catalytic activity and substrate specificity. This study indicates that the screening of enzymes from different plants could be a useful means of identifying enzymes with enhanced catalytic activity and desired substrate specificity. Furthermore, we show that "naturally-evolved" enzymes can be useful in the heterologous production of pharmacologically and industrially important triterpenoids.

Ocimum Genome Sequencing—A Futuristic Therapeutic Mine

Next-generation sequencing (NGS) platforms from the past decade are in the continuous efforts of changing the impact of sequencing on our current knowledge about plant genes, genomes, and their regulation. Holy basil (Ocimum tenuiflorum L. or sanctum L.) genome sequencing has also paved the path for deeper exploration of the medicinal properties of this beneficial herb making it a true ‘elixir of life.’ The draft genome sequence of the holy basil has not only opened the avenues for the drug discovery but has also widened the prospects of the molecular breeding for development of new improved plant varieties.

Triterpene Structural Diversification by Plant Cytochrome P450 Enzymes

Cytochrome P450 monooxygenases (P450s) represent the largest enzyme family of the plant metabolism. Plants typically devote about 1% of the protein-coding genes for the P450s to execute primary metabolism and also to perform species-specific specialized functions including metabolism of the triterpenes, isoprene-derived 30-carbon compounds. Triterpenes constitute a large and structurally diverse class of natural products with various industrial and pharmaceutical applications. P450-catalyzed structural modification is crucial for the diversification and functionalization of the triterpene scaffolds. In recent times, a remarkable progress has been made in understanding the function of the P450s in plant triterpene metabolism. So far, ∼80 P450s are assigned biochemical functions related to the plant triterpene metabolism. The members of the subfamilies CYP51G, CYP85A, CYP90B-D, CYP710A, CYP724B, and CYP734A are generally conserved across the plant kingdom to take part in plant primary metabolism related to the biosynthesis of essential sterols and steroid hormones. However, the members of the subfamilies CYP51H, CYP71A,D, CYP72A, CYP81Q, CYP87D, CYP88D,L, CYP93E, CYP705A, CYP708A, and CYP716A,C,E,S,U,Y are required for the metabolism of the specialized triterpenes that might perform species-specific functions including chemical defense toward specialized pathogens. Moreover, a recent advancement in high-throughput sequencing of the transcriptomes and genomes has resulted in identification of a large number of candidate P450s from diverse plant species. Assigning biochemical functions to these P450s will be of interest to extend our knowledge on triterpene metabolism in diverse plant species and also for the sustainable production of valuable phytochemicals.