Involvement of an ent-copalyl diphosphate synthase in tissue-specific accumulation of specialized diterpenes in Andrographis paniculata

ApCPS2 contributes to medicinal diterpenoid biosynthesis and defense against insect herbivore in Andrographis paniculata

Kalmegh (Andrographis paniculata) spatiotemporally produces medicinally-important ent-labdane-related diterpenoids (ent-LRDs); andrographolide (AD), 14-deoxy-11,12-didehydroandrographolide (DDAD), neoandrographolide (NAD). ApCPS1 and ApCPS2, the ent-copalyl pyrophosphate (ent-CPP)-producing class II diterpene synthases (diTPSs) were identified, but their contributions to ent-CPP precursor supply for ent-LRD biosynthesis were not well understood. Here, we characterized ApCPS4, an additional ent-CPP-forming diTPS. Further, we elucidated in planta function of the ent-CPP-producing diTPSs (ApCPS1,2,4) by integrating transcript-metabolite co-profiles, biochemical analysis and gene functional characterization. ApCPS1,2,4 localized to the plastids, where diterpenoid biosynthesis occurs in plants, but ApCPS1,2,4 transcript expression patterns and ent-LRD contents revealed a strong correlation of ApCPS2 expression and ent-LRD accumulation in kalmegh. ApCPS1,2,4 upstream sequences differentially activated β-glucuronidase (GUS) in Arabidopsis and transiently-transformed kalmegh. Similar to higher expression of ApCPS1 in kalmegh stem, ApCPS1 upstream sequence activated GUS in stem/hypocotyl of Arabidopsis and kalmegh. However, ApCPS2,4 upstream sequences weakly activated GUS expression in Arabidopsis, which was not well correlated with ApCPS2,4 transcript expression in kalmegh tissues. Whereas, ApCPS2,4 upstream sequences could activate GUS expression at a considerable level in kalmegh leaf and roots/calyx, respectively, suggesting the involvement of transcriptional regulator(s) of ApCPS2,4 that might participate in kalmegh-specific diterpenoid pathway. Interestingly, ApCPS2-silenced kalmegh showed a drastic reduction in AD, DDAD and NAD contents and compromised defense against insect herbivore Spodoptera litura. However, ent-LRD contents and herbivore defense in ApCPS1 or ApCPS4-silenced plants remained largely unaltered. Overall, these results suggested an important role of ApCPS2 in producing ent-CPP for medicinal ent-LRD biosynthesis and defense against insect herbivore.

Full-length transcriptome profiling of Acanthopanax gracilistylus provides new insight into the kaurenoic acid biosynthesis pathway

Acanthopanax gracilistylus is a deciduous plant in the family Araliaceae, which is commonly used in Chinese herbal medicine, as the root bark has functions of nourishing the liver and kidneys, removing dampness and expelling wind, and strengthening the bones and tendons. Kaurenoic acid (KA) is the main effective substance in the root bark of A. gracilistylus with strong anti-inflammatory effects. To elucidate the KA biosynthesis pathway, second-generation (DNA nanoball) and third-generation (Pacific Biosciences) sequencing were performed to analyze the transcriptomes of the A. gracilistylus leaves, roots, and stems. Among the total 505,880 isoforms, 408,954 were annotated by seven major databases. Sixty isoforms with complete open reading frames encoding 11 key enzymes involved in the KA biosynthesis pathway were identified. Correlation analysis between isoform expression and KA content identified a total of eight key genes. Six key enzyme genes involved in KA biosynthesis were validated by real-time quantitative polymerase chain reaction. Based on the sequence analysis, the spatial structure of ent-kaurene oxidase was modeled, which plays roles in the three continuous oxidations steps of KA biosynthesis. This study greatly enriches the transcriptome data of A. gracilistylus and facilitates further analysis of the function and regulation mechanism of key enzymes in the KA biosynthesis pathway.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01436-7.

Integrating Transcriptome and Chemical Analyses to Provide Insights into Biosynthesis of Terpenoids and Flavonoids in the Medicinal Industrial Crop Andrographis paniculate and Its Antiviral Medicinal Parts

Andrographis paniculata is a medicinal plant traditionally used to produce diterpene lactones and flavonoids, which possess various biological activities. Widely distributed in China, India, and other Southeast Asia countries, A. paniculata has become an important economic crop, significantly treating SARS-CoV-2, and is being cultivated on a large scale in southern China. The biosynthesis of active ingredients in A. paniculata are regulated and controlled by genes, but their specific roles are still not fully understood. To further explore the growth regulation factors and utilization of its medicinal parts of this industrial crop, chemical and transcriptome analyses were conducted on the roots, stems, and leaves of A. paniculata to identify the biosynthesis pathways and related candidate genes of the active ingredients. The chemical analysis revealed that the main components of A. paniculata were diterpene lactones and flavonoids, which displayed potential ability to treat SARS-CoV-2 through molecular docking. Moreover, the transcriptome sequencing annotated a total of 40,850 unigenes, including 7962 differentially expressed genes. Among these, 120 genes were involved in diterpene lactone biosynthesis and 60 genes were involved in flavonoid biosynthesis. The expression of diterpene lactone-related genes was the highest in leaves and the lowest in roots, consistent with our content determination results. It is speculated that these highly expressed genes in leaves may be involved in the biosynthesis pathway of diterpenes. Furthermore, two class Ⅰ terpene synthases in A. paniculata transcriptome were also annotated, providing reference for the downstream pathway of the diterpene lactone biosynthesis. With their excellent market value, our experiments will promote the study of the biosynthetic genes for active ingredients in A. paniculata and provide insights for subsequent in vitro biosynthesis.

Sequence-Structure Analysis Unlocking the Potential Functional Application of the Local 3D Motifs of Plant-Derived Diterpene Synthases

Plant-derived diterpene synthases (PdiTPSs) play a critical role in the formation of structurally and functionally diverse diterpenoids. However, the specificity or functional-related features of PdiTPSs are not well understood. For a more profound insight, we collected, constructed, and curated 199 functionally characterized PdiTPSs and their corresponding 3D structures. The complex correlations among their sequences, domains, structures, and corresponding products were comprehensively analyzed. Ultimately, our focus narrowed to the geometric arrangement of local structures. We found that local structural alignment can rapidly localize product-specific residues that have been validated by mutagenesis experiments. Based on the 3D motifs derived from the residues around the substrate, we successfully searched diterpene synthases (diTPSs) from the predicted terpene synthases and newly characterized PdiTPSs, suggesting that the identified 3D motifs can serve as distinctive signatures in diTPSs (I and II class). Local structural analysis revealed the PdiTPSs with more conserved amino acid residues show features unique to class I and class II, whereas those with fewer conserved amino acid residues typically exhibit product diversity and specificity. These results provide an attractive method for discovering novel or functionally equivalent enzymes and probing the product specificity in cases where enzyme characterization is limited.

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.

Whole transcriptome analysis identifies full-length genes for neoandrographolide biosynthesis from Andrographis alata, an alternate source for antiviral compounds

Andrographolide and related compounds are effective against several viral diseases, including dengue, COVID-19, influenza, and chikungunya. Andrographis paniculata is the primary source for these compounds, but its availability is limited. A. alata is a potential alternative source, and neoandrographolide (NAG) is the major antiviral compound in this species. Since molecular studies in A. alata are scarce, we sequenced its leaf transcriptome to identify the full-length genes involved in neoandrographolide biosynthesis. We assembled 13.6 Gb RNA-Seq data and generated 81,361 transcripts with 1007 bp average length and 1,810 bp N50. The transcripts were categorized under biological processes (2,707), cellular components (678), and molecular functions (2,036). KEGG analysis mapped 975 transcripts to the secondary metabolite pathways. Among the 420 transcripts mapped to terpenoids and polyketides pathways, 142 transcripts were related to the biosynthesis of andrographolide and its derivatives. After a detailed analysis of these transcripts, we identified 32 full-length genes coding for all the 22 enzymes needed for andrographolide biosynthesis. Among them, 15 full-length genes were identified for the first time from Andrographis species. These full-length genes and the transcripts shall serve as an invaluable resource for the metabolic engineering of andrographolides and neoandrographolide in Andrographis and other species.

Biotechnological production of diterpenoid lactones from cell and organ cultures of Andrographis paniculata

Andrographis paniculata (AP) is a medicinal plant that is traditionally used in Indian, Chinese, Malay, Thai, and Oriental system of medicines to treat various disorders. AP consists of andrographolide (AD), 14-deoxy-11,12-didehydroandrographolide (DDAD), and neoandrographolide (NAD) as major diterpene lactones which has extremely bitter properties; therefore, AP is commonly called "King of bitters." AD, DDAD, and NAD are reported to possess therapeutic values such as antioxidant, immunostimulatory, hepatoprotective, anti-cancer, anti-inflammatory, anti-rheumatoidal, anti-malarial, anti-leishmanial, anti-fertility, anti-obesity, antipyretic, and antimicrobial attributes. According to the Indian Pharmacopoeia, the leaves and tender shoots of AP yield up to 1%, 0.16%, and 0.11% of AD, DDAD, and NAD, respectively, on a dry-weight basis. However, variability in the accumulation of AD, DDAD, and NAD in plants has been reported with respect to species, genotype, season, phenological stage, plant part used, and geography of a region of cultivation. Therefore, cell and tissue culture systems especially cell, shoot, and adventitious root cultures are explored as alternatives for constant and higher production of AD, DDAD, and NAD. This review explores the prospects of exploiting the plant cell and tissue culture systems for the controlled production of AD, DDAD, and NAD. Various strategies such as elicitation by using biological and chemical elicitors are explored for the enhancement of accumulation of AD, DDAD, and NAD in cell and organ cultures. KEY POINTS: • This review explores the possibilities of diterpene lactone production from cell and organ cultures. • Various strategies are explored for the enhanced accumulation of AD, DDAD, and NAD in cell and organ cultures. • Prospects of diterpene lactone production are highlighted.

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.

Recent progress and new perspectives for diterpenoid biosynthesis in medicinal plants

Diterpenoids, including more than 18,000 compounds, represent an important class of metabolites that encompass both phytohormones and some industrially relevant compounds. These molecules with complex, diverse structures and physiological activities, have high value in the pharmaceutical industry. Most medicinal diterpenoids are extracted from plants. Major advances in understanding the biosynthetic pathways of these active compounds are providing unprecedented opportunities for the industrial production of diterpenoids by metabolic engineering and synthetic biology. Here, we summarize recent developments in the field of diterpenoid biosynthesis from medicinal herbs. An overview of the pathways and known biosynthetic enzymes is presented. In particular, we look at the main findings from the past decade and review recent progress in the biosynthesis of different groups of ringed compounds. We also discuss diterpenoid production using synthetic biology and metabolic engineering strategies, and draw on new technologies and discoveries to bring together many components into a useful framework for diterpenoid production.

Arsenic-induced differential expression of oxidative stress and secondary metabolite content in two genotypes of Andrographis paniculata

The present study explores the differential responses of two genotypes (APw_C: wild collection and AP_MS: mass selection line) of A. paniculata against the three application rates of arsenic (42, 126, and 200 mg kg^-1). The oxidative enzymes, As accumulation in different tissues, plant growth, and content of pharmacologically important ent-labdane-related diterpenes (ent-LRDs) of the two genotypes were evaluated in the study. Results demonstrated that As uptake significantly reduced plant biomass in APw_C and AP_MS by 5-41.5% and 9-33% in a dose-response manner, respectively. The AP_MS exhibited lower bioconcentration and translocation factors, higher As tolerance index, and higher content of ent-LRDs as compared to AP_WC. As treatment induced a decrease in the sum of four metabolite content of AP_MS (1.43 times) and an increase in that of AP_WC (1.12 times) as compared to control. Likewise, variance in the production of 5,7,2',3'-tetramethoxyflavanone, and stress enzymes was also observed between APw_C and AP_MS. The increase in the expression of ApCPS2 suggested its involvement in channeling of metabolic flux towards the biosynthesis of ent-LRDs under As stress.

Resource allocation strategies among vegetative growth, sexual reproduction, asexual reproduction and defense during growing season of Aconitum kusnezoffii Reichb

Natural plants must actively allocate their limited resources for survival and reproduction. Although vegetative growth, sexual reproduction, asexual reproduction and defense are all basic processes in the life cycle of plants, the strategies used to allocate resources between these processes are poorly understood. These processes are conspicuous in naturally grown Aconitum kusnezoffii Reichb., which makes it a suitable study subject. Here, the morphology, dry matter, total organic carbon, total nitrogen and aconitum alkaloid levels of shoot, principal root (PR) and lateral roots were measured throughout the growing season. Then, transcriptome and metabolite content analyses were performed. We found that vegetative growth began first. After vegetative growth ceased, sexual development began. Flower organ development was accompanied by increased photosynthesis and the PR consumed temporarily stored resources after flower formation. Asexual propagule development initiated earlier than sexual reproduction and kept accumulating resources after that. Development was slow before flower formation, mainly manifesting as increasing length; then, after flower formation it accelerated via enhanced material transport and accumulation. Defense compounds were maintained at low levels before flowering. In particular, the turnover of defense compounds was enhanced before and after flower bud emergence, providing resources for other processes. After flower formation, defense compounds were accumulated. The pattern found herein provides a vivid example for further studies on resource allocation strategies. The exciting finding that the PR, as a more direct storage site for photosynthate, is a buffer unit for resources, and that defense compounds can be reused for other processes, suggests a need to explore potential mechanisms.

Engineering a Carotenoid-Overproducing Strain of Azospirillum brasilense for Heterologous Production of Geraniol and Amorphadiene

Escherichia coli and Saccharomyces cerevisiae have been used extensively for heterologous production of a variety of secondary metabolites. Neither has an endogenous high-flux isoprenoid pathway, required for the production of terpenoids. Azospirillum brasilense, a nonphotosynthetic GRAS (generally recognized as safe) bacterium, produces carotenoids in the presence of light. The carotenoid production increases multifold upon inactivating a gene encoding an anti-sigma factor (ChrR1). We used this A. brasilense mutant (Car-1) as a host for the heterologous production of two high-value phytochemicals, geraniol and amorphadiene. Cloned genes (crtE1 and crtE2) of A. brasilense encoding native geranylgeranyl pyrophosphate synthases (GGPPS), when overexpressed and purified, did not produce geranyl pyrophosphate (GPP) in vitro Therefore, we cloned codon-optimized copies of the Catharanthus roseus genes encoding GPP synthase (GPPS) and geraniol synthase (GES) to show the endogenous intermediates of the carotenoid biosynthetic pathway in the Car-1 strain were utilized for the heterologous production of geraniol in A. brasilense Similarly, cloning and expression of a codon-optimized copy of the amorphadiene synthase (ads) gene from Artemisia annua also led to the heterologous production of amorphadiene in Car-1. Geraniol or amorphadiene content was estimated using gas chromatography-mass spectrometry (GC-MS) and GC. These results demonstrate that Car-1 is a promising host for metabolic engineering, as the naturally available endogenous pool of the intermediates of the carotenoid biosynthetic pathway of A. brasilense can be effectively utilized for the heterologous production of high-value phytochemicals.IMPORTANCE To date, the major host organisms used for the heterologous production of terpenoids, i.e., E. coli and S. cerevisiae, do not have high-flux isoprenoid pathways and involve tedious metabolic engineering to increase the precursor pool. Since carotenoid-producing bacteria carry endogenous high-flux isoprenoid pathways, we used a carotenoid-producing mutant of A. brasilense as a host to show its suitability for the heterologous production of geraniol and amorphadiene as a proof-of-concept. The advantages of using A. brasilense as a model system include (i) dispensability of carotenoids and (ii) the possibility of overproducing carotenoids through a single mutation to exploit high carbon flux for terpenoid production.

Analysis of Germin-like Protein Genes (OsGLPs) Family in Rice Using Various In silico Approaches

Background:

Germin-like Proteins (GLPs) play an important role in various stresses. Rice contains 43 GLPs, among which many remain functionally unexplored. The computational analysis will provide significant insight into their function.

Objective:

To find various structural properties, functional importance, phylogeny and expression pattern of all OsGLPs using various bioinformatics tools.

Methods:

Physiochemical properties, sub-cellular localization, domain composition, Nglycosylation and Phosphorylation sites, and 3D structural models of the OsGLPs were predicted using various bioinformatics tools. Functional analysis was carried out with the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) and Blast2GO servers. The expression profile of the OsGLPs was predicted by retrieving the data for expression values from tissuespecific and hormonal stressed array libraries of RiceXPro. Their phylogenetic relationship was computed using Molecular and Evolutionary Genetic Analysis (MEGA6) tool.

Results:

Most of the OsGLPs are stable in the cellular environment with a prominent expression in the extracellular region (57%) and plasma membrane (33%). Besides, 3 basic cupin domains, 7 more were reported, among which NTTNKVGSNVTLINV, FLLAALLALASWQAI, and MASSSF were common to 99% of the sequences, related to bacterial pathogenicity, peroxidase activity, and peptide signal activity, respectively. Structurally, OsGLPs are similar but functionally they are diverse with novel enzymatic activities of oxalate decarboxylase, lyase, peroxidase, and oxidoreductase. Expression analysis revealed prominent activities in the root, endosperm, and leaves. OsGLPs were strongly expressed by abscisic acid, auxin, gibberellin, cytokinin, and brassinosteroid. Phylogenetically they showed polyphyletic origin with a narrow genetic background of 0.05%. OsGLPs of chromosome 3, 8, and 12 are functionally more important due to their defensive role against various stresses through co-expression strategy.

Conclusion:

The analysis will help to utilize OsGLPs in future food programs.

The genome of the medicinal plant Andrographis paniculata provides insight into the biosynthesis of the bioactive diterpenoid neoandrographolide

Andrographis paniculata is a herbaceous dicot plant widely used for its anti-inflammatory and anti-viral properties across its distribution in China, India and other Southeast Asian countries. A. paniculata was used as a crucial therapeutic treatment during the influenza epidemic of 1919 in India, and is still used for the treatment of infectious disease in China. A. paniculata produces large quantities of the anti-inflammatory diterpenoid lactones andrographolide and neoandrographolide, and their analogs, which are touted to be the next generation of natural anti-inflammatory medicines for lung diseases, hepatitis, neurodegenerative disorders, autoimmune disorders and inflammatory skin diseases. Here, we report a chromosome-scale A. paniculata genome sequence of 269 Mb that was assembled by Illumina short reads, PacBio long reads and high-confidence (Hi-C) data. Gene annotation predicted 25 428 protein-coding genes. In order to decipher the genetic underpinning of diterpenoid biosynthesis, transcriptome data from seedlings elicited with methyl jasmonate were also obtained, which enabled the identification of genes encoding diterpenoid synthases, cytochrome P450 monooxygenases, 2-oxoglutarate-dependent dioxygenases and UDP-dependent glycosyltransferases potentially involved in diterpenoid lactone biosynthesis. We further carried out functional characterization of pairs of class-I and -II diterpene synthases, revealing the ability to produce diversified labdane-related diterpene scaffolds. In addition, a glycosyltransferase able to catalyze O-linked glucosylation of andrograpanin, yielding the major active product neoandrographolide, was also identified. Thus, our results demonstrate the utility of the combined genomic and transcriptomic data set generated here for the investigation of the production of the bioactive diterpenoid lactone constituents of the important medicinal herb A. paniculata.

Molecular cloning and functional characterization of multiple geranylgeranyl pyrophosphate synthases (ApGGPPS) from Andrographis paniculata

We found that ApGGPPS1, ApGGPPS2, and ApGGPPS3 can convert IPP and DMAPP to GGPP. ApGGPPS2 is probably involved in andrographolide biosynthesis. ApGGPPS3 may be responsible for the synthesis of the cytosolic GGPP. Andrographis paniculata is a traditional herb for the treatment of sore throat, flu, upper respiratory tract infections and other disorders. In A. paniculata, GGPP is not only the precursor of andrographolide and its primary bioactive compounds, but also the precursor of chlorophylls, carotenoids, gibberellins, and abscisic acid, which are the biomolecules of photosynthesis, growth regulation and other physiological and ecological processes. In this study, four cDNAs (named ApGGPPS1, ApGGPPS2, ApGGPPS3 and ApGGPPS4) encoding geranylgeranyl pyrophosphate synthases from A. paniculata were putatively isolated. Bioinformatic and phylogenetic analyses suggested that these ApGGPPS are highly similar to the geranylgeranyl pyrophosphate synthases in other plants. Prokaryotic expression showed that ApGGPPS1, ApGGPPS2 and ApGGPPS3 could convert IPP and DMAPP to GGPP, although ApGGPPS4 lacks a similar function. The expression of ApGGPPS2 was similar as ApCPS2 under MeJA treatment, ApCPS2 involved in the biosynthesis pathway of andrographolide (Shen et al., Biotechnol Lett 38:131-137, 2016a), has been proven through Virus-induced Gene Siliencing (VIGS) (Shen et al., Acta Bot Boreal 36:17-22, 2016b), and the subcellular localization of ApGGPPS2 was shown to localize in the plastid, suggested that ApGGPPS2 could be the key synthase in the biosynthesis pathway of andrographolide. In addition, ApGGPPS3 was shown to localize in the cytoplasm, suggested that ApGGPPS3 may be responsible for the synthesis of cytosolic GGPP, which may participate in the synthesis of cytosolic oligoprenols as side chains to produce ubiquinone, dolichols or other isoprenoids, in the synthesis of polyisoprenoids, and in protein prenylation.

Anti-cancer labdane diterpenoids from adventitious roots of Andrographis paniculata: augmentation of production prospect endowed with pathway gene expression

Andrographolide (AD) is the time-honoured pharmacologically active constituent of the traditionally renowned medicinal plant-Andrographis paniculata. Advancements in the target-oriented drug discovery process have further unravelled the immense therapeutic credibility of another unique molecule-neoandrographolide (NAD). The escalated market demand of these anti-cancer diterpenes is increasingly facing unrelenting hurdles of demand and supply disparity, attributable to their limited yield. Callus and adventitious root cultures were generated to explore their biosynthetic potentials which first time revealed NAD production along with AD. Optimization of the types and concentrations of auxins along with media form and cultivation time led to the successful tuning towards establishing adventitious roots as a superior production alternative for both AD/NAD. Supplementation of IBA to the NAA + Kn-containing MS medium boosted the overall growth and AD/NAD synthesis in the adventitious roots. Compared to control leaves, the adventitious root exhibited about 2.61- and 8.8-fold higher contents of AD and NAD, respectively. The qRT-PCR involving nine key pathway genes was studied, which revealed upregulation of GGPS1 and HMGR1/2 genes and downregulation of DXS1/2 and HDR1/2 genes in the adventitious root as compared to that in the control leaves. Such observations highlight that in vitro cultures can serve as efficient production alternatives for AD/NAD as the cytosolic genes (HMGR1/2 of MVA pathway) are competent enough to take over from the plastidial genes (DXS1/2 and HDR1/2 of MEP pathway), provided the accredited first branch-point regulatory gene (GGPS) expression and the culture requirements are optimally fulfilled.

De Novo RNA Sequencing and Expression Analysis of Aconitum carmichaelii to Analyze Key Genes Involved in the Biosynthesis of Diterpene Alkaloids

Aconitum carmichaelii is an important medicinal herb used widely in China, Japan, India, Korea, and other Asian countries. While extensive research on the characterization of metabolic extracts of A. carmichaelii has shown accumulation of numerous bioactive metabolites including aconitine and aconitine-type diterpene alkaloids, its biosynthetic pathway remains largely unknown. Biosynthesis of these secondary metabolites is tightly controlled and mostly occurs in a tissue-specific manner; therefore, transcriptome analysis across multiple tissues is an attractive method to identify the molecular components involved for further functional characterization. In order to understand the biosynthesis of secondary metabolites, Illumina-based deep transcriptome profiling and analysis was performed for four tissues (flower, bud, leaf, and root) of A. carmichaelii, resulting in 5.5 Gbps clean RNA-seq reads assembled into 128,183 unigenes. Unigenes annotated as possible rate-determining steps of an aconitine-type biosynthetic pathway were highly expressed in the root, in accordance with previous reports describing the root as the accumulation site for these metabolites. We also identified 21 unigenes annotated as cytochrome P450s and highly expressed in roots, which represent candidate unigenes involved in the diversification of secondary metabolites. Comparative transcriptome analysis of A. carmichaelii with A. heterophyllum identified 20,232 orthogroups, representing 30,633 unigenes of A. carmichaelii, gene ontology enrichment analysis of which revealed essential biological process together with a secondary metabolic process to be highly enriched. Unigenes identified in this study are strong candidates for aconitine-type diterpene alkaloid biosynthesis, and will serve as useful resources for further validation studies.

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

The medicinal plant sweet basil (Ocimum basilicum) accumulates bioactive ursane- and oleanane-type pentacyclic triterpenes (PCTs), ursolic acid and oleanolic acid, respectively, in a spatio-temporal manner; however, the biosynthetic enzymes and their contributions towards PCT biosynthesis remain to be elucidated. Two CYP716A subfamily cytochrome P450 monooxygenases (CYP716A252 and CYP716A253) are identified from a methyl jasmonate-responsive expression sequence tag collection and functionally characterized, employing yeast (Saccharomyces cerevisiae) expression platform and adapting virus-induced gene silencing (VIGS) in sweet basil. CYP716A252 and CYP716A253 catalyzed sequential three-step oxidation at the C-28 position of α-amyrin and β-amyrin to produce ursolic acid and oleanolic acid, respectively. Although CYP716A253 was more efficient than CYP716A252 for amyrin C-28 oxidation in yeast, VIGS revealed essential roles for both of these CYP716As in constitutive biosynthesis of ursolic acid and oleanolic acid in sweet basil leaves. However, CYP716A253 played a major role in elicitor-induced biosynthesis of ursolic acid and oleanolic acid. Overall, the results suggest similar as well as distinct roles of CYP716A252 and CYP716A253 for the spatio-temporal biosynthesis of PCTs. CYP716A252 and CYP716A253 might be useful for the alternative and sustainable production of PCTs in microbial host, besides increasing plant metabolite content through genetic modification.

Genoproteomics-assisted improvement of Andrographis paniculata: toward a promising molecular and conventional breeding platform for autogamous plants affecting the pharmaceutical industry

Andrographis paniculata (Burm. f.) Wall. ex Nees. (AP) is a hermaphroditic, self-compatible, and habitual inbreeding plant. Its main bioactive component is andrographolide, which is capable of inducing autophagic cell death in some human cancer cells and helps fight HIV/AIDS. Increasing the andrographolide content by investigating the genetic mechanisms controlling its biosynthesis in order to improve and develop high-yielding cultivars are the main breeding targets for AP. However, there might exist some limitations or barriers for crossability within AP accessions. Recently, this problem was addressed in AP by using a combination of crossbreeding and biotechnology-aided genetic methods. This review emphasizes that development of a breeding platform in a hard-to-breed plant, such as AP, requires the involvement of a broad range of methods from classical genetics to molecular breeding. To this end, a phenological stage (for example, flowering and stigma development) can be simplified to a quantitative morphological trait (for example, bud or stigma length) to be used as an index to express the highest level of receptivity in order to manage outcrossing. The outcomes of the basic crossability research can be then employed in diallel mating and crossbreeding. This review explains how genomic data could produce useful information regarding genetic distance and its influence on the crossability of AP accessions. Our review indicates that co-dominant DNA markers, such as microsatellites, are also capable of resolving the evolutionary pathway and cryptic features of plant populations and such information can be used to select the best breeding strategy. This review also highlights the importance of proteomic analysis as a breeding tool. In this regard, protein diversification, as well as the impact of normal and stress-responsive proteins on morphometric and physiological behaviors, could be used in breeding programs. These findings have immense potential for improving plant production and, therefore, can be regarded as prospective breeding platforms for medicinal plants that have an autogamous mode of reproduction. Finally, this review suggests that novel site-directed genome editing approaches such as TALENs (Transcription Activator-Like Effector Nucleases) and CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 (CRISPR-associated protein-9 nuclease) systems together with other new plant breeding technologies (NPBT) should simultaneously be taken into consideration for improvement of pharmaceutical plants.

A thaumatin-like protein of Ocimum basilicum confers tolerance to fungal pathogen and abiotic stress in transgenic Arabidopsis

Plant often responds to fungal pathogens by expressing a group of proteins known as pathogenesis-related proteins (PRs). The expression of PR is mediated through pathogen-induced signal-transduction pathways that are fine-tuned by phytohormones such as methyl jasmonate (MeJA). Here, we report functional characterization of an Ocimum basilicum PR5 family member (ObTLP1) that was identified from a MeJA-responsive expression sequence tag collection. ObTLP1 encodes a 226 amino acid polypeptide that showed sequence and structural similarities with a sweet-tasting protein thaumatin of Thaumatococcus danielli and also with a stress-responsive protein osmotin of Nicotiana tabacum. The expression of ObTLP1 in O. basilicum was found to be organ-preferential under unstressed condition, and responsive to biotic and abiotic stresses, and multiple phytohormone elicitations. Bacterially-expressed recombinant ObTLP1 inhibited mycelial growth of the phytopathogenic fungi, Scleretonia sclerotiorum and Botrytis cinerea; thereby, suggesting its antifungal activity. Ectopic expression of ObTLP1 in Arabidopsis led to enhanced tolerance to S. sclerotiorum and B. cinerea infections, and also to dehydration and salt stress. Moreover, induced expression of the defense marker genes suggested up-regulation of the defense-response pathways in ObTLP1-expressing Arabidopsis upon fungal challenge. Thus, ObTLP1 might be useful for providing tolerance to the fungal pathogens and abiotic stresses in crops.