The activity of the artemisinic aldehyde Δ11(13) reductase promoter is important for artemisinin yield in different chemotypes of Artemisia annua L

Diversified quantity, gene structure, and expression profile of OPR gene family of A. annua

Artemisia annua, the source of artemisinin production, is a traditional herb used for treating malaria for thousand years. The genetic background is of high heterozygosity and traits (plant height, biomass, artemisinin content, etc.) are diverse across different germplasms. Unraveling the key genes associated with growth and secondary metabolism is essential for the efficient production of artemisinin. The 12-oxo-phytodienoic acid reductase (OPR) genes, crucial for plant growth and development and stress resistance, remain unexplored in A. annua. In this study, nine OPR genes (named as AaOPR1 to AaOPR9) were identified in A. annua, including two pairs of genes formed from recent tandem duplications. The number of OPRs varied among different haplotype genomes, and each OPR gene exhibiting distinct expression pattern. Moreover, the OPR family displayed evolutionarily activity with significant variations in numbers and gene structures observed across different plant species. Widespread gene duplication of OPRs, observed in the majority of analyzed plant genomes, brought evolutionary potential. DBR2, a member of AaOPRs involved in artemisinin biosynthesis, had two copies (AaOPR1/DBR2.1 and AaOPR2/DBR2.2) with different expression patterns, one of which was a recently generated copy with a significant 7-amino acids truncation. Heterologous protein expression and functional characterization of the two copies of DBR2 yielded multiple isomers with identical molecular weights but different arrangements, indicating neofunctionalization of the newly generated copy. The polymorphism within the OPR gene family merely scratches the surface of the genetic diversity in A. annua, and further investigation of genetic features is needed for the screening of elite germplasm resources.

Enhancing Food Security via selecting Superior Camelina (Camelina sativa L.) parents: a positive approach incorporating pheno-morphological traits, fatty acids composition, and Tocopherols Content

BACKGROUND

Preserving plant genetic resources is essential for tackling global food security challenges. Effectively meeting future agricultural demands requires comprehensive and efficient assessments of genetic diversity in breeding programs and germplasm from gene banks. This research investigated the diversity of pheno-morphological traits, along with the fatty acid and tocopherol content and composition, in 135 double haploid lines of camelina.

RESULTS

The number of sub-branches, siliques number of main-branch and sub-branch, and seeds number in siliques of the main-branch displayed notable coefficients of variation with values of 33.19%, 30.32%, 29.23%, and 23.81% respectively. Within the current investigation, the measurements of height, sub-branch number, and thousand seed weight varied from 53.50 to 86.50 cm, 3.50 to 14, and 0.73 to 1.52 g, respectively. The analysis unveiled that the average content of omega-3, omega-6, and omega-9 fatty acids in the examined lines was approximately 33%, 20%, and 17%, respectively. The total tocopherol content varied between 675 and 877 ppm, predominantly consisting of gamma-tocopherol, which accounted for over 95% of the total content. The fatty acid C18:2 displayed a markedly strong positive correlation with alpha-tocopherol (0.99**), while C18:3 exhibited positive correlations with gamma-tocopherol (0.98**) and total tocopherol (0.98**). Furthermore, a positive correlation was evident between C20:1 and delta-tocopherol (0.98**). The scrutinized lines, specifically lines 35, 72, 94, and 126 demonstrated notable attributes regarding yield and yield components. Conversely, in the realm of biochemical traits, lines 35, 66, 47, 30, 65, 135, 83, 27, 4, 77, 62, 81, and 93 stood out for their elevated potential. The gene expression analysis related to the tocopherol biosynthesis pathway revealed distinct expression patterns. Specifically, the VTE1 gene exhibited the highest level of expression. In contrast, the VTE3 gene displayed the lowest level of expression compared to other genes.

CONCLUSIONS

The study's findings hold great potential for improving food security by enabling the selection of superior camelina parent plants based on specific traits. This approach can drive the development of high-yielding varieties with enhanced nutritional value and better-quality camelina oil.

Co-regulatory network analysis of the main secondary metabolite (SM) biosynthesis in Crocus sativus L

Saffron (Crocus sativus L.) is being embraced as the most important medicinal plant and the commercial source of saffron spice. Despite the beneficial economic and medicinal properties of saffron, the regulatory mechanism of the correlation of TFs and genes related to the biosynthesis of the apocarotenoids pathway is less obvious. Realizing these regulatory hierarchies of gene expression networks related to secondary metabolites production events is the main challenge owing to the complex and extensive interactions between the genetic behaviors. Recently, high throughput expression data have been highly feasible for constructing co-regulation networks to reveal the regulated processes and identifying novel candidate hub genes in response to complex processes of the biosynthesis of secondary metabolites. Herein, we performed Weighted Gene Co-expression Network Analysis (WGCNA), a systems biology method, to identify 11 regulated modules and hub TFs related to secondary metabolites. Three specialized modules were found in the apocarotenoids pathway. Several hub TFs were identified in notable modules, including MADS, C2H2, ERF, bZIP, HD-ZIP, and zinc finger protein MYB and HB, which were potentially associated with apocarotenoid biosynthesis. Furthermore, the expression levels of six hub TFs and six co-regulated genes of apocarotenoids were validated with RT-qPCR. The results confirmed that hub TFs specially MADS, C2H2, and ERF had a high correlation (P < 0.05) and a positive effect on genes under their control in apocarotenoid biosynthesis (CCD2, GLT2, and ADH) among different C. sativus ecotypes in which the metabolite contents were assayed. Promoter analysis of the co-expressed genes of the modules involved in apocarotenoids biosynthesis pathway suggested that not only are the genes co-expressed, but also share common regulatory motifs specially related to hub TFs of each module and that they may describe their common regulation. The result can be used to engineer valuable secondary metabolites of C. sativus by manipulating the hub regulatory TFs.

Promoter variations in DBR2-like affect artemisinin production in different chemotypes of Artemisia annua

Artemisia annua is the only known plant source of the potent antimalarial artemisinin, which occurs as the low- and high-artemisinin producing (LAP and HAP) chemotypes. Nevertheless, the different mechanisms of artemisinin producing between these two chemotypes were still not fully understood. Here, we performed a comprehensive analysis of genome resequencing, metabolome, and transcriptome data to systematically compare the difference in the LAP chemotype JL and HAP chemotype HAN. Metabolites analysis revealed that 72.18% of sesquiterpenes was highly accumulated in HAN compared to JL. Integrated omics analysis found a DBR2-Like (DBR2L) gene may be involved in artemisinin biosynthesis. DBR2L was highly homologous with DBR2, belonged to ORR3 family, and had the DBR2 activity of catalyzing artemisinic aldehyde to dihydroartemisinic aldehyde. Genome resequencing and promoter cloning revealed that complicated variations existed in DBR2L promoters among different varieties of A. annua and were clustered into three variation types. The promoter activity of diverse variant types showed obvious differences. Furthermore, the core region (-625 to 0) of the DBR2L promoter was identified and candidate transcription factors involved in DBR2L regulation were screened. Thus, the result indicates that DBR2L is another key enzyme involved in artemisinin biosynthesis. The promoter variation in DBR2L affects its expression level, and thereby may result in the different yield of artemisinin in varieties of A. annua. It provides a novel insight into the mechanism of artemisinin-producing difference in LAP and HAP chemotypes of A. annua, and will assist in a high yield of artemisinin in A. annua.

Allele-aware chromosome-level genome assembly of Artemisia annua reveals the correlation between ADS expansion and artemisinin yield

Artemisia annua is the major natural source of artemisinin, an anti-malarial medicine commonly used worldwide. Here, we present chromosome-level haploid maps for two A. annua strains with different artemisinin contents to explore the relationships between genomic organization and artemisinin production. High-fidelity sequencing, optical mapping, and chromatin conformation capture sequencing were used to assemble the heterogeneous and repetitive genome and resolve the haplotypes of A. annua. Approximately 50,000 genes were annotated for each haplotype genome, and a triplication event that occurred approximately 58.12 million years ago was examined for the first time in this species. A total of 3,903,467-5,193,414 variants (SNPs, indels, and structural variants) were identified in the 1.5-Gb genome during pairwise comparison between haplotypes, consistent with the high heterozygosity of this species. Genomic analyses revealed a correlation between artemisinin concents and the copy number of amorpha-4,11-diene synthase genes. This correlation was further confirmed by resequencing of 36 A. annua samples with varied artemisinin contents. Circular consensus sequencing of transcripts facilitated the detection of paralog expression. Collectively, our study provides chromosome-level allele-aware genome assemblies for two A. annua strains and new insights into the biosynthesis of artemisinin and its regulation, which will contribute to conquering malaria worldwide.

Toward understanding of the methoxylated flavonoid biosynthesis pathway in Dracocephalum kotschyi Boiss

Nowadays, with the development and advancement of next-generation sequencing technologies, a new path has been provided for transcriptomic studies. In this study, the transcriptome of Dracocephalum kotschyi Boiss., as an endemic and endangered plant which is contained a large amount of valuable secondary metabolites with antioxidant and anticancer properties, was sequenced. Then functional annotation and gene ontology analysis for 165,597 assembled transcripts were performed, most were associated with the metabolic pathways. This might be because there are various active biochemical pathways in this plant. Furthermore, after comprehensive transcript annotation, the putative genes involved in the main metabolic pathways of D. kotschyi were identified. Then, the biosynthetic pathway of its valuable methoxylated flavones was proposed. Finally, the accumulations of important methoxylated-flavone metabolites in three different tissues were quantified by HPLC. The relative expression of the genes involved in the proposed pathway was investigated by qRT-PCR, which indicated high expression levels in the bud tissue. The present results may lead to the design strategies to preserve the genetic diversity of endangered D. kotschyi plants and apply the new methods for engineering its valuable methoxylated-flavones pathway.

Comprehensive Map of the Artemisia annua Proteome and Quantification of Differential Protein Expression in Chemotypes Producing High versus Low Content of Artemisinin

Artemisia annua is well known for biosynthesizing the antimalarial drug artemisinin. Here, a global proteomic profiling of A. annua is conducted with identification of a total of 13 403 proteins based on the genome sequence annotation database. Furthermore, a spectral library is generated to perform quantitative proteomic analysis using data independent acquisition mass spectrometry. Specifically, proteins between two chemotypes that produce high (HAP) and low (LAP) artemisinin content, respectively, are comprehensively quantified and compared. 182 proteins are identified with abundance significantly different between these two chemotypes means after the statistic use the p-value and fold change it is found 182 proteins can reach the demand conditions which represent the expression are significantly different between the high artemisnin content plants (HAPs) and the low artemisnin content plants (LAPs). Data are available via ProteomeXchange with identifier PXD015547. Overall, this current study globally identifies the proteome of A. annua and quantitatively compares the targeted sub-proteomes between the two cultivars of HAP and LAP, providing systematic information on metabolic pathways of A. annua.

An oxidatively stressful situation: a case of Artemisia annua L

Artemisinin (ART) is an antimalarial compound that possesses a variety of novel biological activities. Due to the low abundance of ART in natural sources, agricultural supply has been erratic, and prices are highly volatile. While heterologous biosynthesis and semi-synthesis are advantageous in certain aspects, these approaches remained disadvantageous in terms of productivity and cost-effectiveness. Therefore, further improvement in ART production calls for approaches that should supplement the agricultural production gap, while reducing production costs and stabilising supply. The present review offers a discussion on the elicitation of plants and/or in vitro cultures as an economically feasible yield enhancement strategy to address the global problem of access to affordable ART. Deemed critical for the manipulation of biosynthetic potential, the mechanism of ART biosynthesis is reviewed. It includes a discussion on the current biotechnological solutions to ART production, focusing on semi-synthesis and elicitation. A brief commentary on the possible aspects that influence elicitation efficiency and how oxidative stress modulates ART synthesis is also presented. Based on the critical analysis of current literature, a hypothesis is put forward to explain the possible involvement of enzymes in assisting the final non-enzymatic transformation step leading to ART formation. This review highlights the critical factors limiting the success of elicitor-induced modulation of ART metabolism, that will help inform strategies for future improvement of ART production. Additionally, new avenues for future research based on the proposed hypothesis will lead to exciting perspectives in this research area and continue to enhance our understanding of this intricate metabolic process.

New insights into diosgenin biosynthesis pathway and its regulation in Trigonella foenum-graecum L

INTRODUCTION

Throughout history, thousands of medicinal and aromatic plants have been widely utilised by people worldwide. Owing to them possessing of valuable compounds with little side effects in comparison with chemical drugs, herbs have been of interest to humans for a number of purposes. Diosgenin, driven from fenugreek, Trigonella foenum-graecum L., has extensively drawn scientist's attention owing to having curable properties and being a precursor of steroid hormones synthesis. Nonetheless, complete knowledge about the biosynthesis pathway of this metabolite is still elusive.

OBJECTIVE

In the present research, we isolated the full-length CDS of 14 genes involving in diosgenin formation and measured their expression rate in various genotypes, which had illustrated different amount of diosgenin.

METHODOLOGY

The genes were successfully isolated, and functional motifs were also assessed using in silico approaches.

RESULTS

Moreover, combining transcript and metabolite analysis revealed that there are many genes playing the role in diosgenin formation, some of which are highly influential. Among them, ∆²⁴ -reductase, which converts cycloartenol to cycloartanol, is the first-committed and rate-limiting enzyme in this pathway. Additionally, no transcripts indicating to the presence or expression of lanosterol synthase were detected, contradicting the previous hypothesis about the biosynthetic pathway of diosgenin in fenugreek.

CONCLUSION

Considering all these, therefore, we propose the most possible pathway of diosgenin. This knowledge will then pave the way toward cloning the genes as well as engineering the diosgenin biosynthesis pathway.

Insights into Heterologous Biosynthesis of Arteannuin B and Artemisinin in Physcomitrella patens

: Metabolic engineering is an integrated bioengineering approach, which has made considerable progress in producing terpenoids in plants and fermentable hosts. Here, the full biosynthetic pathway of artemisinin, originating from Artemisia annua, was integrated into the moss Physcomitrella patens. Different combinations of the five artemisinin biosynthesis genes were ectopically expressed in P. patens to study biosynthesis pathway activity, but also to ensure survival of successful transformants. Transformation of the first pathway gene, ADS, into P. patens resulted in the accumulation of the expected metabolite, amorpha-4,11-diene, and also accumulation of a second product, arteannuin B. This demonstrates the presence of endogenous promiscuous enzyme activity, possibly cytochrome P450s, in P. patens. Introduction of three pathway genes, ADS-CYP71AV1-ADH1 or ADS-DBR2-ALDH1 both led to the accumulation of artemisinin, hinting at the presence of one or more endogenous enzymes in P. patens that can complement the partial pathways to full pathway activity. Transgenic P. patens lines containing the different gene combinations produce artemisinin in varying amounts. The pathway gene expression in the transgenic moss lines correlates well with the chemical profile of pathway products. Moreover, expression of the pathway genes resulted in lipid body formation in all transgenic moss lines, suggesting that these may have a function in sequestration of heterologous metabolites. This work thus provides novel insights into the metabolic response of P. patens and its complementation potential for A. annua artemisinin pathway genes. Identification of the related endogenous P. patens genes could contribute to a further successful metabolic engineering of artemisinin biosynthesis, as well as bioengineering of other high-value terpenoids in P. patens.

In planta and in silico characterization of five sesquiterpene synthases from Vitis vinifera (cv. Shiraz) berries

Five Vitis vinifera sesquiterpene synthases were characterized, two was previously uncharacterized, one being a caryophyllene/cubebene synthase and the other a cadinene synthase. Residue differences with other Vitis sesquiterpene synthases are described. The biochemical composition of grape berries at harvest can have a profound effect on the varietal character of the wine produced. Sesquiterpenes are an important class of volatile compounds produced in grapes that contribute to the flavor and aroma of wine, making the elucidation of their biosynthetic origin an important field of research. Five cDNAs corresponding to sesquiterpene synthase genes (TPSs) were isolated from Shiraz berries and expressed in planta in Nicotiana benthamiana followed by chemical characterization by GC-MS. Three of the TPS cDNAs were isolated from immature berries and two were isolated from ripe Shiraz berries. Two of the investigated enzymes, TPS26 and TPS27, have been previously investigated by expression in E. coli, and the in planta products generally correspond to these previous studies. The enzyme TPS07 differed by eight amino acids (none of which are in the active site) from germacrene B and D synthase isolated from Gewürztraminer grapes and characterized in vitro. Here in planta characterization of VvShirazTPS07 yielded ylangene, germacrene D and several minor products. Two of the enzymes isolated from immature berries were previously uncharacterized enzymes. VvShirazTPS-Y1 produced cadinene as a major product and at least 17 minor sesquiterpenoid skeletons. The second, VvShirazTPS-Y2, was characterized as a caryophyllene/cubebene synthase, a combination of products not previously reported from a single enzyme. Using in silico methods, we identified residues that could play key roles regarding differences in product formation of these enzymes. The first ring closure that is either a 1,10- or 1,11-ring closure is likely controlled by three neighboring amino acids in helices G1, H2, and J. As for many other investigated TPS enzymes, we also observe that only a few residues can account for radical changes in product formation.

Jasmonate promotes artemisinin biosynthesis by activating the TCP14-ORA complex in Artemisia annua

Artemisia annua produces the valuable medicinal component, artemisinin, which is a sesquiterpene lactone widely used in malaria treatment. AaORA, a homolog of CrORCA3, which is involved in activating terpenoid indole alkaloid biosynthesis in Catharanthus roseus, is a jasmonate (JA)-responsive and trichome-specific APETALA2/ETHYLENE-RESPONSE FACTOR that plays a pivotal role in artemisinin biosynthesis. However, the JA signaling mechanism underlying AaORA-mediated artemisinin biosynthesis remains enigmatic. Here, we report that AaORA forms a transcriptional activator complex with AaTCP14 (TEOSINTE BRANCHED 1/CYCLOIDEA/PROLIFERATING CELL FACTOR 14), which is also predominantly expressed in trichomes. AaORA and AaTCP14 synergistically bind to and activate the promoters of two genes, double bond reductase 2 (DBR2) and aldehyde dehydrogenase 1 (ALDH1), both of which encode enzymes vital for artemisinin biosynthesis. AaJAZ8, a repressor of the JA signaling pathway, interacts with both AaTCP14 and AaORA and represses the ability of the AaTCP14-AaORA complex to activate the DBR2 promoter. JA treatment induces AaJAZ8 degradation, allowing the AaTCP14-AaORA complex to subsequently activate the expression of DBR2, which is essential for artemisinin biosynthesis. These data suggest that JA activation of the AaTCP14-AaORA complex regulates artemisinin biosynthesis. Together, our findings reveal a novel artemisinin biosynthetic pathway regulatory network and provide new insight into how specialized metabolism is modulated by the JA signaling pathway in plants.

An investigation of the HMGR gene and IPI gene expression in black caraway (Bunium persicum)

Black caraway is of great importance for its terpene compounds. Many genes are involved in the biosynthesis of secondary metabolites in medicinal plants. For this study, black caraway seeds were collected from five different regions, i.e. [Isfahan; Kerman (Khabr); Semnan; Kerman (Sirch); and Hormozgan]. The black caraway seed oil was extracted and analyzed by means of the gas chromatography method. There was a negatively significant correlation (p ≤ 0.05) observed between cuminaldehyde and gammaterpinene compounds. 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) and isopentenyl pyrophosphate isomerase (IPI) play an important role in the biosynthesis of secondary metabolites. Appropriate primers were designed for these genes based on the conserved regions in other plants. Amplified fragments were then sequenced. Blastn results indicated the similarity of the high RNA sequences between new sequences and other HMGR and IPI gene sequences in GenBank, and it also identified the HMGR and IPI gene sequences of B. persicum. A fragment of the HMGR gene with KJ143741 number was recorded in the gene bank. Quantitative PCR showed that the relative expression of two genes in different growth stages of B. persicum was significantly different between the germination stage and the multi-leaf stage, and also between the germination stage and the flowering stage (p < 0.05); however, there was no significant difference observed between the flowering stage and the multi-leaf stage. The results indicated that the expression of HMGR increased from the germination stage to the adult plant, and then it got stable until the flowering stage; in the same vein, the expression of IPI increased continuously from the germination stage to the flowering stage. The expression of HMGR and IPI genes occurred differently at the germination stage of five ecotypes. The Hormozgan ecotype showed the least expression rate.

Expression of key genes affecting artemisinin content in five Artemisia species

Artemisinin, an effective anti-malarial drug is synthesized in the specialized 10-celled biseriate glandular trichomes of some Artemisia species. In order to have an insight into artemisinin biosynthesis in species other than A. annua, five species with different artemisinin contents were investigated for the expression of key genes that influence artemisinin content. The least relative expression of the examined terpene synthase genes accompanied with very low glandular trichome density (4 No. mm⁻²) and absence of artemisinin content in A. khorassanica (S2) underscored the vast metabolic capacity of glandular trichomes. A. deserti (S4) with artemisinin content of 5.13 mg g⁻¹ DW had a very high expression of Aa-ALDH1 and Aa-CYP71AV1 and low expression of Aa-DBR2. It is possible to develop plants with high artemisinin synthesis ability by downregulating Aa-ORA in S4, which may result in the reduction of Aa-ALDH1 and Aa-CYP71AV1 genes expression and effectively change the metabolic flux to favor more of artemisinin production than artemisinic acid. Based on the results, the Aa-ABCG6 transporter may be involved in trichome development. S4 had high transcript levels and larger glandular trichomes (3.46 fold) than A. annua found in Iran (S1), which may be due to the presence of more 2C-DNA (3.48 fold) in S4 than S1.

The effects of promoter variations of the N-Methylcanadine 1-Hydroxylase (CYP82Y1) gene on the noscapine production in opium poppy

Noscapine is an antitumor alkaloid produced in opium poppy (Papaver somniferum) and some members of the Papaveraceae family. It has been primarily used for its antitussive effects; more recently, its anticancer properties were shown. Herein, we detected an SSR embedded in the promoter region of the CYP82Y1 gene, which was found to be the first committed-step enzyme in the noscapine biosynthesis pathway, using the MISA program. Some collected ecotypes of P. somniferum were investigated for understanding of SSRs role in the regulation of gene expression and metabolite content. Quantitative PCR showed that a variation in the motif repeat number (either a decrease or increase) down-regulated the expression of the CYP82Y1 gene. Furthermore, the analysis of noscapine content suggested that a variation in the promoter region influence noscapine amount. Moreover, P. bracteatum was analyzed in both transcript and metabolite levels, and illustrated much less expression and metabolite level in comparison to P. somniferum. By exploiting the transcriptome data from the eight genera of the Papaveraceae family, we found that noscapine biosynthesis genes are present in P. bracteatum and are not shared in other genera of the Papaveraceae family. This results may explain production of a confined metabolite within a genus.

Detailed Phytochemical Analysis of High- and Low Artemisinin-Producing Chemotypes of Artemisia annua

Chemical derivatives of artemisinin, a sesquiterpene lactone produced by Artemisia annua, are the active ingredient in the most effective treatment for malaria. Comprehensive phytochemical analysis of two contrasting chemotypes of A. annua resulted in the characterization of over 80 natural products by NMR, more than 20 of which are novel and described here for the first time. Analysis of high- and low-artemisinin producing (HAP and LAP) chemotypes of A. annua confirmed the latter to have a low level of DBR2 (artemisinic aldehyde Δ¹¹⁽¹³⁾ reductase) gene expression. Here we show that the LAP chemotype accumulates high levels of artemisinic acid, arteannuin B, epi-deoxyarteannuin B and other amorpha-4,11-diene derived sesquiterpenes which are unsaturated at the 11,13-position. By contrast, the HAP chemotype is rich in sesquiterpenes saturated at the 11,13-position (dihydroartemisinic acid, artemisinin and dihydro-epi-deoxyarteannunin B), which is consistent with higher expression levels of DBR2, and also with the presence of a HAP-chemotype version of CYP71AV1 (amorpha-4,11-diene C-12 oxidase). Our results indicate that the conversion steps from artemisinic acid to arteannuin B, epi-deoxyarteannuin B and artemisitene in the LAP chemotype are non-enzymatic and parallel the non-enzymatic conversion of DHAA to artemisinin and dihyro-epi-deoxyarteannuin B in the HAP chemotype. Interestingly, artemisinic acid in the LAP chemotype preferentially converts to arteannuin B rather than the endoperoxide bridge containing artemisitene. In contrast, in the HAP chemotype, DHAA preferentially converts to artemisinin. Broader metabolomic and transcriptomic profiling revealed significantly different terpenoid profiles and related terpenoid gene expression in these two morphologically distinct chemotypes.

An Efficient Chemoenzymatic Synthesis of Dihydroartemisinic Aldehyde

Artemisinin from the plant Artemisia annua is the most potent pharmaceutical for the treatment of malaria. In the plant, the sesquiterpene cyclase amorphadiene synthase, a cytochrome-dependent CYP450, and an aldehyde reductase convert farnesyl diphosphate (FDP) into dihydroartemisinic aldehyde (DHAAl), which is a key intermediate in the biosynthesis of artemisinin and a semisynthetic precursor for its chemical synthesis. Here, we report a chemoenzymatic process that is able to deliver DHAAl using only the sesquiterpene synthase from a carefully designed hydroxylated FDP derivative. This process, which reverses the natural order of cyclization of FDP and oxidation of the sesquiterpene hydrocarbon, provides a significant improvement in the synthesis of DHAAl and demonstrates the potential of substrate engineering in the terpene synthase mediated synthesis of high-value natural products.

Prolonged exposure to salt stress affects specialized metabolites-artemisinin and essential oil accumulation in Artemisia annua L.: metabolic acclimation in preferential favour of enhanced terpenoid accumulation accompanying vegetative to reproductive phase transition

Artemisia annua accumulates substantial quantities of unique and highly useful antimalarial sesquiternoid artemisinin and related phytomolecules as well as its characteristic essential oil in its glandular trichomes. The phytomolecules are mainly produced in its leaves and inflorescences. Artemisia annua plants were grown under NaCl salinity (50, 100 and 200 mM) stress conditions imposed throughout the entire life cycle of the plant. Results revealed that specialized metabolites like artemisinin, arteannuin-B, artemisinic acid + dihydroartemisinic acid and essential oil accumulation were positively modulated by NaCl salinity stress. Interestingly, total content of monoterpenoids and sesquiterpenoids of essential oil was induced by NaCl salinity treatment, contrary to previous observations. Production of camphor, the major essential oil constituent was induced under the influence of treatment. The metabolic acclimation and manifestations specific to terpenoid pathway are analysed vis-a-vis vegetative to reproductive periods and control of the modulation. WRKY and CYP71AV1 play a key role in mediating the responses through metabolism in glandular trichomes. The distinctness of the salinity induced responses is discussed in light of differential mechanism of adaptation to abiotic stresses and their impact on terpenoid-specific metabolic adjustments in A. annua. Results provide potential indications of possible adaptation of A. annua under saline conditions for agrarian techno-economic benefaction.

Compartmentalized Metabolic Engineering for Artemisinin Biosynthesis and Effective Malaria Treatment by Oral Delivery of Plant Cells

Artemisinin is highly effective against drug-resistant malarial parasites, which affects nearly half of the global population and kills >500 000 people each year. The primary cost of artemisinin is the very expensive process used to extract and purify the drug from Artemisia annua. Elimination of this apparently unnecessary step will make this potent antimalarial drug affordable to the global population living in endemic regions. Here we reported the oral delivery of a non-protein drug artemisinin biosynthesized (∼0.8 mg/g dry weight) at clinically meaningful levels in tobacco by engineering two metabolic pathways targeted to three different cellular compartments (chloroplast, nucleus, and mitochondria). The doubly transgenic lines showed a three-fold enhancement of isopentenyl pyrophosphate, and targeting AACPR, DBR2, and CYP71AV1 to chloroplasts resulted in higher expression and an efficient photo-oxidation of dihydroartemisinic acid to artemisinin. Partially purified extracts from the leaves of transgenic tobacco plants inhibited in vitro growth progression of Plasmodium falciparum-infected red blood cells. Oral feeding of whole intact plant cells bioencapsulating the artemisinin reduced the parasitemia levels in challenged mice in comparison with commercial drug. Such novel synergistic approaches should facilitate low-cost production and delivery of artemisinin and other drugs through metabolic engineering of edible plants.

Root regulation of artemisinin production in Artemisia annua: trichome and metabolite evidence

Roots of plants with high artemisinin-producing leaves increased leaf production of artemisinin in low-producing plants and vice versa indicating roots are involved in controlling artemisinin biosynthesis in shoots. The anti-malarial sesquiterpene, artemisinin, is produced and stored in glandular trichomes (GLTs) of Artemisia annua. Evidence suggested roots, which produce no significant artemisinin nor precursor compounds, regulate production of artemisinin biosynthesis in the leaves. Using grafting, we studied the relationship between rootstock and scion by measuring GLTs and five artemisinic metabolites (artemisinin, deoxyartemisinin, dihydroartemisinic acid, artemisinic acid, arteannuin B) in scions of ungrafted, self-grafted, and cross-grafted plants among three cultivars: S and 15 both having GLTs with artemisinin at 1.49 and 0.57 %, respectively, and G producing neither GLTs nor detectable artemisinin. All artemisinin-producing self-grafts, e.g., S/S (scion/rootstock) and 15/15, produced more artemisinin than ungrafted plants, likely from grafting stress. S/S grafts also produced more GLTs. The 15/S grafts produced more artemisinin than S/15, suggesting rootstocks from high producing S plants stimulated artemisinin production in 15 scions. S/15 grafts yielded less artemisinin than S/S, but more than either 15/15 or ungrafted n15 and nS; S/15 grafts also had a lower density of GLTs than S/S, suggesting rootstock inhibition of the scion. The S rootstock induced trace artemisinin production in G scions, but did not induce GLT formation in G/S grafts. Different grafts exhibited different trichome morphologies and effects on artemisinic pathway flux. This study provides new information regarding the role of roots in GLT development and artemisinin production in this important medicinal plant.

Artemisinin-based antimalarial research: application of biotechnology to the production of artemisinin, its mode of action, and the mechanism of resistance of Plasmodium parasites

Malaria is a worldwide disease caused by Plasmodium parasites. A sesquiterpene endoperoxide artemisinin isolated from Artemisia annua was discovered and has been accepted for its use in artemisinin-based combinatorial therapies, as the most effective current antimalarial treatment. However, the quantity of this compound produced from the A. annua plant is very low, and the availability of artemisinin is insufficient to treat all infected patients. In addition, the emergence of artemisinin-resistant Plasmodium has been reported recently. Several techniques have been applied to enhance artemisinin availability, and studies related to its mode of action and the mechanism of resistance of malaria-causing parasites are ongoing. In this review, we summarize the application of modern technologies to improve the production of artemisinin, including our ongoing research on artemisinin biosynthetic genes in other Artemisia species. The current understanding of the mode of action of artemisinin as well as the mechanism of resistance against this compound in Plasmodium parasites is also presented. Finally, the current situation of malaria infection and the future direction of antimalarial drug development are discussed.

The jasmonate-responsive AaMYC2 transcription factor positively regulates artemisinin biosynthesis in Artemisia annua

The plant Artemisia annua is well known due to the production of artemisinin, a sesquiterpene lactone that is widely used in malaria treatment. Phytohormones play important roles in plant secondary metabolism, such as jasmonic acid (JA), which can induce artemisinin biosynthesis in A. annua. Nevertheless, the JA-inducing mechanism remains poorly understood. The expression of gene AaMYC2 was rapidly induced by JA and AaMYC2 binds the G-box-like motifs within the promoters of gene CYP71AV1 and DBR2, which are key structural genes in the artemisinin biosynthetic pathway. Overexpression of AaMYC2 in A. annua significantly activated the transcript levels of CYP71AV1 and DBR2, which resulted in an increased artemisinin content. By contrast, artemisinin content was reduced in the RNAi transgenic A. annua plants in which the expression of AaMYC2 was suppressed. Meanwhile, the RNAi transgenic A. annua plants showed lower sensitivity to methyl jasmonate treatment than the wild-type plants. These results demonstrate that AaMYC2 is a positive regulator of artemisinin biosynthesis and is of great value in genetic engineering of A. annua for increased artemisinin production.

Overexpression of AaWRKY1 Leads to an Enhanced Content of Artemisinin in Artemisia annua

Artemisinin is an effective component of drugs against malaria. The regulation of artemisinin biosynthesis is at the forefront of artemisinin research. Previous studies showed that AaWRKY1 can regulate the expression of ADS, which is the first key enzyme in artemisinin biosynthetic pathway. In this study, AaWRKY1 was cloned, and it activated ADSpro and CYPpro in tobacco using dual-LUC assay. To further study the function of AaWRKY1, pCAMBIA2300-AaWRKY1 construct under 35S promoter was generated. Transgenic plants containing AaWRKY1 were obtained, and four independent lines with high expression of AaWRKY1 were analyzed. The expression of ADS and CYP, the key enzymes in artemisinin biosynthetic pathway, was dramatically increased in AaWRKY1-overexpressing A. annua plants. Furthermore, the artemisinin yield increased significantly in AaWRKY1-overexpressing A. annua plants. These results showed that AaWRKY1 increased the content of artemisinin by regulating the expression of both ADS and CYP. It provides a new insight into the mechanism of regulation on artemisinin biosynthesis via transcription factors in the future.

Molecular Farming in Artemisia annua, a Promising Approach to Improve Anti-malarial Drug Production

Malaria is a parasite infection affecting millions of people worldwide. Even though progress has been made in prevention and treatment of the disease; an estimated 214 million cases of malaria occurred in 2015, resulting in 438,000 estimated deaths; most of them occurring in Africa among children under the age of five. This article aims to review the epidemiology, future risk factors and current treatments of malaria, with particular focus on the promising potential of molecular farming that uses metabolic engineering in plants as an effective anti-malarial solution. Malaria represents an example of how a health problem may, on one hand, influence the proper development of a country, due to its burden of the disease. On the other hand, it constitutes an opportunity for lucrative business of diverse stakeholders. In contrast, plant biofarming is proposed here as a sustainable, promising, alternative for the production, not only of natural herbal repellents for malaria prevention but also for the production of sustainable anti-malarial drugs, like artemisinin (AN), used for primary parasite infection treatments. AN, a sesquiterpene lactone, is a natural anti-malarial compound that can be found in Artemisia annua. However, the low concentration of AN in the plant makes this molecule relatively expensive and difficult to produce in order to meet the current worldwide demand of Artemisinin Combination Therapies (ACTs), especially for economically disadvantaged people in developing countries. The biosynthetic pathway of AN, a process that takes place only in glandular secretory trichomes of A. annua, is relatively well elucidated. Significant efforts have been made using plant genetic engineering to increase production of this compound. These include diverse genetic manipulation approaches, such as studies on diverse transcription factors which have been shown to regulate the AN genetic pathway and other biological processes. Results look promising; however, further efforts should be addressed toward optimization of the most cost-effective biofarming approaches for synthesis and production of medicines against the malaria parasite.

Identification and expression analyses of MYB and WRKY transcription factor genes in Papaver somniferum L

Papaver somniferum L. is an herbaceous, annual and diploid plant that is important from pharmacological and strategic point of view. The cDNA clones of two putative MYB and WRKY genes were isolated (GeneBank accession numbers KP411870 and KP203854, respectively) from this plant, via the nested-PCR method, and characterized. The MYB transcription factor (TF) comprises 342 amino acids, and exhibits the structural features of the R2R3MYB protein family. The WRKY TF, a 326 amino acid-long polypeptide, falls structurally into the group II of WRKY protein family. Quantitative real-time PCR (qRT-PCR) analyses indicate the presence of these TFs in all organs of P. somniferum L. and Papaver bracteatum L. Highest expression levels of these two TFs were observed in the leaf tissues of P. somniferum L. while in P. bracteatum L. the espression levels were highest in the root tissues. Promoter analysis of the 10 co-expressed gene clustered involved in noscapine biosynthesis pathway in P. somniferum L. suggested that not only these 10 genes are co-expressed, but also share common regulatory motifs and TFs including MYB and WRKY TFs, and that may explain their common regulation.

Proteomic analysis of Artemisia annua--towards elucidating the biosynthetic pathways of the antimalarial pro-drug artemisinin

BACKGROUND

MS-based proteomics was applied to the analysis of the medicinal plant Artemisia annua, exploiting a recently published contig sequence database (Graham et al. (2010) Science 327, 328-331) and other genomic and proteomic sequence databases for comparison. A. annua is the predominant natural source of artemisinin, the precursor for artemisinin-based combination therapies (ACTs), which are the WHO-recommended treatment for P. falciparum malaria.

RESULTS

The comparison of various databases containing A. annua sequences (NCBInr/viridiplantae, UniProt/viridiplantae, UniProt/A. annua, an A. annua trichome Trinity contig database, the above contig database and another A. annua EST database) revealed significant differences in respect of their suitability for proteomic analysis, showing that an organism-specific database that has undergone extensive curation, leading to longer contig sequences, can greatly increase the number of true positive protein identifications, while reducing the number of false positives. Compared to previously published data an order-of-magnitude more proteins have been identified from trichome-enriched A. annua samples, including proteins which are known to be involved in the biosynthesis of artemisinin, as well as other highly abundant proteins, which suggest additional enzymatic processes occurring within the trichomes that are important for the biosynthesis of artemisinin.

CONCLUSIONS

The newly gained information allows for the possibility of an enzymatic pathway, utilizing peroxidases, for the less well understood final stages of artemisinin's biosynthesis, as an alternative to the known non-enzymatic in vitro conversion of dihydroartemisinic acid to artemisinin. Data are available via ProteomeXchange with identifier PXD000703.

Stable heterologous expression of biologically active terpenoids in green plant cells

Plants biosynthesize a great diversity of biologically active small molecules of interest for fragrances, flavors, and pharmaceuticals. Among specialized metabolites, terpenoids represent the greatest molecular diversity. Many terpenoids are very complex, and total chemical synthesis often requires many steps and difficult chemical reactions, resulting in a low final yield or incorrect stereochemistry. Several drug candidates with terpene skeletons are difficult to obtain by chemical synthesis due to their large number of chiral centers. Thus, biological production remains the preferred method for industrial production for many of these compounds. However, because these chemicals are often found in low abundance in the native plant, or are produced in plants which are difficult to cultivate, there is great interest in engineering increased production or expression of the biosynthetic pathways in heterologous hosts. Although there are many examples of successful engineering of microbes such as yeast or bacteria to produce these compounds, this often requires extensive changes to the host organism's metabolism. Optimization of plant gene expression, post-translational protein modifications, subcellular localization, and other factors often present challenges. To address the future demand for natural products used as drugs, new platforms are being established that are better suited for heterologous production of plant metabolites. Specifically, direct metabolic engineering of plants can provide effective heterologous expression for production of valuable plant-derived natural products. In this review, our primary focus is on small terpenoids and we discuss the benefits of plant expression platforms and provide several successful examples of stable production of small terpenoids in plants.