Amorpha-4,11-diene Synthase Research Articles

Reproductive Development Modulates Gene Expression and Metabolite Levels with Possible Feedback Inhibition of Artemisinin in Artemisia annua

The relationship between the transition to budding and flowering in Artemisia annua and the production of the antimalarial sesquiterpene, artemisinin (AN), the dynamics of artemisinic metabolite changes, AN-related transcriptional changes, and plant and trichome developmental changes were measured. Maximum production of AN occurs during full flower stage within floral tissues, but that changes in the leafy bracts and nonbolt leaves as the plant shifts from budding to full flower. Expression levels of early pathway genes known to be involved in isopentenyl diphosphate and farnesyl diphosphate biosynthesis leading to AN were not immediately positively correlated with either AN or its precursors. However, we found that the later AN pathway genes, amorpha-4,11-diene synthase (ADS) and the cytochrome P450, CYP71AV1 (CYP), were more highly correlated with AN's immediate precursor, dihydroartemisinic acid, within all leaf tissues tested. In addition, leaf trichome formation throughout the developmental phases of the plant also appears to be more complex than originally thought. Trichome changes correlated closely with the levels of AN but not its precursors. Differences were observed in trichome densities that are dependent both on developmental stage (vegetative, budding, and flowering) and on position (upper and lower leaf tissue). AN levels declined significantly as plants matured, as did ADS and CYP transcripts. Spraying leaves with AN or artemisinic acid inhibited CYP transcription; artemisinic acid also inhibited ADS transcription. These data allow us to present a novel model for the differential control of AN biosynthesis as it relates to developmental stage and trichome maturation and collapse.

Isolation, characterization and structural studies of amorpha - 4, 11-diene synthase (ADS(3963)) from Artemisia annua L.

With the escalating prevalence of malaria in recent years, artemisinin demand has placed considerable stress on its production worldwide. At present, the relative low-yield of artemisinin (0.01-1.1 %) in the source plant (Artemisia annua L. plant) has imposed a serious limitation in commercializing the drug. Amorpha-4, 11-diene synthase (ADS) has been reported a key enzyme in enhancing the artemisinin level in Artemisia annua L. An understanding of the structural and functional correlations of Amorpha-4, 11-diene synthase (ADS) may therefore, help in the molecular up-regulation of the enzyme. In this context, an in silico approach was used to study the ADS₃₉₆₃ (3963 bp) gene cloned by us, from high artemisinin (0.7-0.9% dry wt basis) yielding strain of A. annua L. The full-length putative gene of ADS₃₉₆₃ was found to encode a protein consisting of 533 amino acid residues with conserved aspartate rich domain. The isoelectric point (pI) and molecular weight of the protein were 5.25 and 62.2 kDa, respectively. The phylogenetic analysis of ADS genes from various species revealed evolutionary conservation. Homology modeling method was used for prediction of the 3D structure of ADS₃₉₆₃ protein and Autodock 4.0 version was used to study the ligand binding. The predicted 3D model and docking studies may further be used in characterizing the protein in wet laboratory.

Effect of Sugars on Artemisinin Production in Artemisia annua L.: Transcription and Metabolite Measurements

The biosynthesis of the valuable sesquiterpene anti-malarial, artemisinin, is known to respond to exogenous sugar concentrations. Here young Artemisia annua L. seedlings (strain YU) were used to measure the transcripts of six key genes in artemisinin biosynthesis in response to growth on sucrose, glucose, or fructose. The measured genes are: from the cytosolic arm of terpene biosynthesis, 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR), farnesyl disphosphate (FPS); from the plastid arm of terpene biosynthesis, 1-deoxyxylulose-5-phosphate synthase (DXS), 1-deoxyxylulouse 5-phosphate reductoisomerase (DXR); from the dedicated artemisinin pathway amorpha-4,11-diene synthase (ADS), and the P450, CYP71AV1 (CYP). Changes in intracellular concentrations of artemisinin (AN) and its precursors, dihydroartemisinic acid (DHAA), artemisinic acid (AA), and arteannuin B (AB) were also measured in response to these three sugars. FPS, DXS, DXR, ADS and CYP transcript levels increased after growth in glucose, but not fructose. However, the kinetics of these transcripts over 14 days was very different. AN levels were significantly increased in glucose-fed seedlings, while levels in fructose-fed seedlings were inhibited; in both conditions this response was only observed for 2 days after which AN was undetectable until day 14. In contrast to AN, on day 1 AB levels doubled in seedlings grown in fructose compared to those grown in glucose. Results showed that transcript level was often negatively correlated with the observed metabolite concentrations. When seedlings were gown in increasing levels of AN, some evidence of a feedback mechanism emerged, but mainly in the inhibition of AA production. Together these results show the complex interplay of exogenous sugars on the biosynthesis of artemisinin in young A. annua seedlings.

Isolation and Characterization of AaWRKY1, an Artemisia annua Transcription Factor that Regulates the Amorpha-4,11-diene Synthase Gene, a Key Gene of Artemisinin Biosynthesis

Amorpha-4,11-diene synthase (ADS) of Artemisia annua catalyzes the conversion of farnesyl diphosphate into amorpha-4,11-diene, the first committed step in the biosynthesis of the antimalarial drug artemisinin. The promoters of ADS contain two reverse-oriented TTGACC W-box cis-acting elements, which are the proposed binding sites of WRKY transcription factors. A full-length cDNA (AaWRKY1) was isolated from a cDNA library of the glandular secretory trichomes (GSTs) in which artemisinin is synthesized and sequestered. AaWRKY1 encodes a 311 amino acid protein containing a single WRKY domain. AaWRKY1 and ADS genes were highly expressed in GSTs and both were strongly induced by methyl jasmonate and chitosan. Transient expression analysis of the AaWRKY1-GFP (green fluorescent protein) reporter revealed that AaWRKY1 was targeted to nuclei. Biochemical analysis demonstrated that the AaWRKY1 protein was capable of binding to the W-box cis-acting elements of the ADS promoters, and it demonstrated transactivation activity in yeast. Co-expression of the effector construct 35S::AaWRKY1 with a reporter construct ADSpro1::GUS greatly activated expression of the GUS (beta-glucuronidase) gene in stably transformed tobacco. Furthermore, transient expression experiments in agroinfiltrated Nicotiana benthamiana and A. annua leaves showed that AaWRKY1 protein transactivated the ADSpro2 promoter activity by binding to the W-box of the promoter; disruption of the W-box abolished the activation. Transient expression of AaWRKY1 cDNA in A. annua leaves clearly activated the expression of the majority of artemisinin biosynthetic genes. These results strongly suggest the involvement of the AaWRKY1 transcription factor in the regulation of artemisinin biosynthesis, and indicate that ADS is a target gene of AaWRKY1 in A. annua.

Terpenoid metabolic profiling analysis of transgenic Artemisia annua L. by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry

Amorpha-4,11-diene synthase (ADS) is a very important enzyme which catalyzes the committed step of artemisinin biosynthesis. In this work, two lines of transgenic Artemisia annua L. which ADS was over-expressed (line A9) and suppressed (line Amsi), respectively, were utilized. And the transgenic line GUS with β-Glucuronidase gene was regarded as the control. Their terpenoid metabolic profiling was investigated by using GC × GC–TOFMS. The metabolic profiling method established included simple extraction, two-dimension separation and multivariate analysis. Partial least squares discriminant analysis (PLS-DA) was used to classify two transgenic lines and the control line. Eleven important compounds in classification were identified. Most of them were sesquiterpenoids including monoterpenoid, diterpenoid and four bioprecursors of artemsisnin. Compared with the control, artemisinin and bioprecursors in the line A9 increased as a result of over-expressing ADS. Borneol and phytol also increased in the line A9, but (E)-β-farnesene and germacrene D were reversely altered. The result indicated that over-expression of the ADS affected not only artemisinin biosynthesis, but also the whole metabolic network of terpenoid. Compared with the line A9, no opposite change of artemisinin and related derivatives was observed in the line Amsi, the ADS inhibition had no significant effect on artemisinin biosynthesis in the line Amsi.

Salicylic acid activates artemisinin biosynthesis in Artemisia annua L.

This paper provides evidence that salicylic acid (SA) can activate artemisinin biosynthesis in Artemisia annua L. Exogenous application of SA to A. annua leaves was followed by a burst of reactive oxygen species (ROS) and the conversion of dihydroartemisinic acid into artemisinin. In the 24 h after application, SA application led to a gradual increase in the expression of the 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) gene and a temporary peak in the expression of the amorpha-4,11-diene synthase (ADS) gene. However, the expression of the farnesyl diphosphate synthase (FDS) gene and the cytochrome P450 monooxygenase (CYP71AV1) gene showed little change. At 96 h after SA (1.0 mM) treatment, the concentration of artemisinin, artemisinic acid and dihydroartemisinic acid were 54, 127 and 72% higher than that of the control, respectively. Taken together, these results suggest that SA induces artemisinin biosynthesis in at least two ways: by increasing the conversion of dihydroartemisinic acid into artemisinin caused by the burst of ROS, and by up-regulating the expression of genes involved in artemisinin biosynthesis.

Synergistic re-channeling of mevalonate pathway for enhanced artemisinin production in transgenic Artemisia annua

To interfere with the endogenous gene encoding squalene synthase (SS) responsible for sterol biosynthesis, an antisense SS cDNA ( asSS) was introduced into the genome of A. annua. Following the decline of SS mRNA and synchronous reduction of total sterols, mRNA coding for amorpha-4,11-diene synthase (ADS) tremendously elevated, whereas mRNAs for sesquiterpene cyclases encompassing 8-epicedrol synthase (EPS), β-caryophyllene synthase (CS) and β-farnesene synthase (FS) declined or kept homeostasis, suggesting a bias in redirection of the partially blocked metabolic flow to amorpha-4,11-diene. By phenotyping the chimeric ADS promoter-fused β-glucuronidase gene ( pADS-GUS), overexpression of the pADS-GUS reporter was detected upon chilling exposure and ultraviolet (UV) irradiation. In transgenic plants that expose to chilling, ADS and EPS were dramatically up-regulated, but CS was down-regulated and FS and SS were unaffected, implying further chilling-induced diversion of carbon flux among sesquiterpenes. Accordingly, ADS and cytochrome P450 reductase (CPR) were also chilling-inducible, while cytochrome P450 monooxygenase (CYP71AV1) reflected a complicated chilling profile. A maximal artemisinin content was accounted for 16.6 mg/g or 3.7-fold increase in a chilled transgenic line. Fascinatingly, an extraordinarily high artemisinin content of 23.5 mg/g or 5.2-fold increase was measured after 15-month storage of the ground powder from the identical chilled transgenic tissue, demonstrating non-enzymatic conversion from a putative artemisinin precursor to artemisinin. Moreover, a relevance of chilling exposure with singlet oxygen ( 1O 2) emission and artemisinin overproduction was established. These results indicated that the mevalonate pathway has been first skewed to amorpha-4, 11-diene and shunted ultimately to artemisinin through a synergy of genetic modification with environmental superinduction.

Increased Accumulation of Artemisinin and Anthocyanins in Artemisia annua Expressing the Arabidopsis Blue Light Receptor CRY1

Artemisinin, an effective drug against Plasmodium species that cause malaria, is a sesquiterpene lactone isolated from Artemisia annua. The yield of artemisinin in plants is relatively low, and it is influenced by various environmental growing conditions. In Arabidopsis, cryptochrome 1 (CRY1) is one of the key receptors that perceive light signals, and its overexpression promotes accumulation of secondary metabolites. In this study, overexpression of Arabidopsis CRY1 in A. annua resulted in increased accumulation of both artemisinin and anthocyanins. Under blue light, transgenic plants expressing high level of AtCRY1 showed a variety of blue light-induced responses, including inhibition of hypocotyl elongation and cotyledon expansion, dwarfism, and purpuring of aerial organs. Reverse transcription polymerase chain reaction analysis revealed that expression levels of the phenylalanine ammonia-lyase- and chalcone synthase-encoding genes were elevated and that anthocyanin accumulation was increased. Expression analysis of genes encoding farnesyl diphosphate synthase (FPS), amorpha-4,11-diene synthase (ADS), and CYP71AV1, three important enzymes in artemisinin biosynthesis, indicated that transcript abundance of all three genes, FPS, ADS, and CYP71AV1, increased in AtCRY1 plants. Based on high performance liquid chromatography analysis, artemisinin content in these plants increased by 30∼40%, when compared to control. These results have demonstrated that alteration of light signaling components could provide a viable approach for enhancing production of the secondary metabolite artemisinin.

The improvement of amorpha-4,11-diene production by a yeast-conform variant

To investigate the effect of the yeast-conform variant of the Artemisia annua gene encoding for amorpha-4,11-diene synthase (ADS) on the production of amorpha-4,11-diene in a transformed yeast. The ADS gene was mutated to the yeast-conform variant ADSm. The ADSm synthesis was performed based on step-by-step extension of a short region of the gene through a series of polymerase chain reactions (PCR). The artificial ADSm gene contained codons preferred by the yeast translation machinery. The sequence was then integrated into a yeast expression vector pYeDP60. The fusion construct was active and the transformed yeast cells produced higher level of amorpha-4,11-diene compared with the plant gene-transformed yeast cells. Strains transformed with the yeast-conform allele (ADSm) were more efficient in terms of production of amorpha-4,11-diene than those transformed with the plant gene. We demonstrated that yeast-conform allele of foreign genes by serial PCR reactions can be a solution to low efficiency of heterologous gene expression in Saccharomyces cerevisiae cells.

Quantification of Three Key Enzymes Involved in Artemisinin Biogenesis in Artemisia annua by Polyclonal Antisera-Based ELISA

To elucidate the fine-tuned temporal and spatial modulation of artemisinin production in annual wormwood (Artemisia annua), we conducted enzyme-linked immunosorbent assay-based immunoquantification of three key enzymes involved in artemisinin biosynthesis, amorpha-4,11-diene synthase (ADS), cytochrome P450 monooxygenase (CYP71AV1), and cytochrome P450 reductase (CPR), in various tissues and under different growth conditions. The field-grown plants accumulate abundant ADS and CYP71AV1 but a trace amount of CPR in all tested tissues. Furthermore, ADS and CYP71AV1 accumulations in leaves are 16- and eightfold higher than in roots, and ten- and fourfold higher than in stems, respectively, demonstrating a tissue-specific expression pattern. Interestingly, the flowering field plants and cold-acclimated cultural plants produce higher levels of ADS and CYP71AV1 than non-flowering field plants or untreated cultural plants, indicating the environmental and developmental induction on ADS and CYP71AV1 genes and providing possible explanation for the observation that elevation of artemisinin level occurs after flowering.

Tissue Specificity and Developmental Pattern of Amorpha-4,11-diene Synthase (ADS) Proved by ADS Promoter-Driven GUS Expression in the Heterologous Plant, Arabidopsis thaliana

Amorpha-4,11-diene synthase (ADS) of Artemisia annua L. is a sesquiterpene cyclase that catalyzes the conversion of farnesyl diphosphate into amorpha-4,11-diene in the biosynthesis of the antimalarial artemisinin. To explore the mechanisms regulating the tissue-specific and developmental distributions of ADS, a full ADS promoter was generated using PCR, and fused to GUS for introduction into Arabidopsis thaliana. ADSpro::GUS fusion transcripts were organ-specific, mainly present in the anthers and trichomes of the green tissues of the juvenile leaves. This result was consistent with the ADS transcription pattern observed in A. annua as examined by RT-PCR. To determine the subcellular localization of ADS, an open reading frame (ORF) of ADS was fused to the green fluorescent protein (smGFP) gene and introduced into the A. thaliana protoplasts. GFP fluorescence was located exclusively in the cytosol, an indication that ADS is a cytosol-localized protein.

Effects of low-dose gamma irradiation on artemisinin content and amorpha-4,11-diene synthase activity in Artemisia annua L

Purpose: This research work aimed to create in vitro plantlet variants of Artemisia annua through gamma irradiation. The obtained variants were then evaluated for the correlation between their artemisinin content and enzyme activity of amorpha-4,11-diene synthase (ADS), the first enzyme of the artemisinin pathway.Materials and methods: Shoot tips from plantlets of A. annua were exposed to gamma rays at a low-dose range and transferred to hormone-free MS medium for in vitro cultivation. A dose-response curve and the value of 50% of lethal dose (LD50) were then obtained. This LD50 dose of gamma rays was used for treating another batch of shoot tips. The surviving plantlets after four subsequent subcultures were evaluated for their ability to accumulate artemisinin in correlation with the enzyme activity of ADS.Results: The dose-response curve showed that the LD50 value was at 8 Gray (Gy). The surviving irradiated plantlets from this dose treatment had artemisinin content ranging from 0.03–0.70% (w/w) of dry weight, comparing with only 0.18% present in the original non-irradiated samples. Their correlation coefficient between the ADS activity and the artemisinin content appeared to be R2 = 0.090 for all the 18 samples tested, although, selectively, more than half of these (11 samples) showed their R2 value of as high as 0.851.Conclusions: There was no correlation between the artemisinin content and ADS activity found in the whole population, but the correlation was observed in the main subpopulation of the irradiated A. annua plantlets.

Cloning, E. coli Expression and Molecular Analysis of Amorpha‐4,11‐Diene Synthase from a High‐Yield Strain of Artemisia annua L.

AbstractIncreasing demand of artemisinin in the treatment of malaria has placed substantial stress on the total artemisinin supplies world‐wide, so more attention has been paid to increasing the content of artemisinin in the Artemisia annua L. plant. In this study, amorpha‐4,11‐diene synthase (ADS) cDNA (ads1) and genomics gene (gads1) were cloned from a high‐yield A. annua strain 001. The activity of ADS1 was confirmed by heterogeneous overexpression of ads1 and in vitro enzymatic incubation. Reverse transcript‐polymerase chain reaction results demonstrated that ads1 expressed in leaves, flowers and young stems, but not in roots. This organ‐specific expression pattern of ads1 is consistent with that of artemisinin accumulation in the plant. The gads1 has a complex organization including seven exons and six introns, and belongs to class III terpene synthase. DNA gel blotting revealed that the ADS gene has at least four copies in the genome of strain 001. The higher copy numbers might be one of the reasons for its high artemisinin content.(Managing editor: Wei Wang)

Improved conditions for production of recombinant plant sesquiterpene synthases in Escherichia coli

Amorpha-4,11-diene synthase (ADS) from Artemisia annua and (+)-germacrene synthase (GDS) from Zingiber officinale were expressed in Escherichia coli under different conditions to optimize the yield of active soluble protein. The cDNAs of these enzymes were inserted into the pET28 vector (Novagen) and expressed in four different bacterial strains; BL21 (DE3), BL21 (DE3) Tuner™, BL21 (DE3) pLysS and BL21 (DE3) pLysS Tuner™ using different inducing agents (IPTG, The Inducer™). The effects of induction under osmotic stress in the presence of glycine betaine and sorbitol were investigated. Although background expression for ADS was reduced when using pLysS strains, no significant difference was noted for ADS activity in soluble whole cell lysates after induction with either IPTG or The Inducer™. For GDS, on the other hand, the change between BL21 (DE3) cells and BL21 (DE3) Tuner™, induced with IPTG, leads to a twofold increase in enzyme activity in the soluble fraction while a reduction in activity is observed when using the pLysS strains. The same doubling of activity is observed for GDS when the commonly used BL.21 (DE3) is induced with The Inducer™. Addition of 2.5 mM glycine betaine and 660 mM sorbitol to the bacterial growth media resulted in reduction of growth rate and biomass yield but under these conditions the best overall protein production, for both enzymes, was obtained. Compared to the standard conditions previously used in our laboratory the yield of soluble active protein was increased 7- and 2.5-fold for ADS and GDS, using BL21 (DE3) pLysS Tuner and BL21 (DE3), respectively.

Cyclization Mechanism of Amorpha-4,11-diene Synthase, a Key Enzyme in Artemisinin Biosynthesis

Cyclization of farnesyl diphosphate into amorpha-4,11-diene by amorpha-4,11-diene synthase (ADS) initiates biosynthesis of artemisinin, a clinically important antimalarial drug precursor. Three possible ring-closure mechanisms, two involving a bisabolyl carbocation intermediate followed by either a 1,3-hydride shift or two successive 1,2-shifts, and one involving a germacrenyl carbocation, were proposed and tested by analyzing the fate of farnesyl diphosphate H-1 hydrogen atoms through (1)H and (2)H NMR spectroscopy. Migration of one deuterium atom of [1,1-(2)H(2)]farnesyl diphosphate to H-10 of amorpha-4,11-diene singled out the bisabolyl carbocation mechanism with a 1,3-hydride shift. Further confirmation was obtained through enzyme reactions with (1R)- and (1S)-[1-(2)H]farnesyl diphosphate. Results showed that deuterium of the 1R compound remained at H-6, whereas that of the 1S compound migrated to H-10 of amorpha-4,11-diene. Incorporation of one deuterium into amorphadiene in the cyclization process was observed when the reaction was performed in (2)H(2)O, as evidenced by an increase of 1 amu in the mass of the molecular ion.

A single-vial analytical and quantitative gas chromatography–mass spectrometry assay for terpene synthases

A quantitative assay for the analysis of sesquiterpene synthases, wherein each reaction mixture is formulated in glass gas chromatography vials, overlaid with organic solvent such as ethyl acetate, and subsequently vortexed to extract hydrocarbon reaction products into the organic phase after a suitable incubation period, was developed. The product-enriched organic phase is then sampled in an automated fashion and injected directly into a gas chromatograph–mass spectrometer without further workup for analysis and quantification of hydrocarbon products. Application of the vial assay to the analysis of amorpha-4,11-diene synthase (ADS), a sesquiterpene synthase, demonstrated the sensitivity of the assay for detection of major and minor reaction products and most notably for the identification of several sesquiterpene products that had escaped previous detection. A steady-state kinetic analysis of tobacco 5-epi-aristolochene synthase (TEAS), another sesquiterpene synthase, validated the quantitative nature of the assay, providing an alternative means to the established method of using radiolabeled substrate, extraction, and scintillation counting. This simplified assay provides a standardized method to facilitate analysis of terpene synthases and diverse mutant enzyme libraries by supplanting the common practice of using larger scale reactions, multiple extractions, and evaporative concentration of the organic phase prior to gas chromatography–mass spectrometry (GC-MS) analysis.

Photosynthesis in plant life

Artemisinin, an endoperoxide sesquiterpene lactone, is an effective antimalarial drug isolated from Artemisia annua L. In this study, a low dose (1.44 kJ m−2 d−1) of UV-B radiation (280–320 nm) for short-term (1 h per day for 10 days) was applied to A. annua seedlings to stimulate artemisinin production. UV-B treatment not only induced the generation of reactive oxygen species (ROS), enhanced peroxidase activity and endogenous content of abscisic acid (ABA), but stimulated the biosynthesis of artemisinin in the seedlings. Here, transcriptomic changes during UV-B radiation in A. annua were detected using an Agilent GeneChip with 43,692 probe sets. In total, 358 transcripts were identified as differentially expressed under UV-B stress, of which 172 transcripts increased and 186 transcripts decreased in abundance. In terms of biological processes, gene ontology (GO) terms including primary carbohydrate and nitrogen compound metabolic processes were enriched in UV-B-repressed genes. The up-regulated genes were enriched in response to stress, ROS generation, hormone (ethylene, ABA) stimulus and cell cycle control. The expression of key enzymes such as amorpha-4,11-diene synthase (ADS) and cytochrome P450 dependent monooxygenase/hydroxylase (CYP71AV1), and related WRKY transcription factors was up-regulated significantly for artemisinin biosynthesis. This profile of global gene expression patterns during UV-B stress will be valuable for further identification of the enzymes involved in artemisinin biosynthesis.