Red and Blue Light Promote the Accumulation of Artemisinin in Artemisia Annua L

Genome-wide identification and expression analysis of the ADH gene family in Artemisia annua L. under UV-B stress

ADHs are key genes that catalyze the interconversion between alcohols and aldehydes, which play crucial roles in plant adaptation to a range of abiotic stresses. However, the characterization and evolutionary pathways of ADH genes in the antimalarial plant Artemisia annua are still unclear. This study identified 49 ADH genes in A. annua and conducted a detailed analysis of their structural features, conserved motifs, and duplication types, revealing that tandem and dispersed duplications are the primary mechanisms of gene expansion. Evolutionary analysis of ADH genes between A. annua (AanADH) and A. argyi (AarADH) revealed dynamic changes, with 35 genes identified deriving from their most recent common ancestor in both species. ADH1, crucial for artemisinin production, had two copies in both species, expanding via dispersed duplication in A. annua but whole-genome duplication in A. argyi. CREs and WGCNA analysis suggested that AanADH genes may be regulated by UV-B stress. Following short-term UV-B treatment, 16 DEGs were identified, including ADH1 (AanADH6 and AanADH7), and these genes were significantly downregulated after two hours treatment (UV2h) and upregulated after four hours treatment (UV4h). The expression changes of these genes were further confirmed by GO enrichment analysis and qRT-PCR experiments. Overall, this study comprehensively characterized the ADH gene family in A. annua and systematically identified AanADH genes that were responsive to UV-B stress, providing a foundation for further research on their roles in abiotic stress responses.

TmCOP1-TmHY5 module-mediated blue light signal promotes chicoric acid biosynthesis in Taraxacum mongolicum

Chicoric acid, a phenolic compound derived from plants, exhibits a range of pharmacological activities. Light significantly influences the chicoric acid biosynthesis in Taraxacum mongolicum; however, the transcriptional regulatory network governing this process remains unclear. A combined analysis of the metabolome and transcriptome revealed that blue light markedly enhances chicoric acid accumulation compared to red light. The blue light-sensitive transcription factor ELONGATED HYPOCOTYL5 (HY5) is closely associated with multiple core proteins, transcription factors and chicoric acid synthase genes involved in light signalling. Both in vivo and in vitro experiments demonstrated that TmHY5 directly regulates several chicoric acid biosynthetic genes, including TmPAL3, Tm4CL1 and TmHQT2. Additionally, TmHY5 promotes the accumulation of luteolin and anthocyanins by increasing the expression of TmCHS2 and TmANS2. The E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) forms a protein complex with TmHY5, significantly inhibiting chicoric acid biosynthesis. Blue light inhibits TmCOP1-TmHY5 complex protein formation while enhancing the expression levels of TmCOP1 through TmHY5. Furthermore, TmHY5 elevates the expression levels of TmbZIP1, which indirectly activates Tm4CL1 expression. In vivo, TmCOP1 directly inhibits the expression of the TmHY5-Tm4CL1 complex. Therefore, we speculate that TmCOP1-TmHY5-mediated blue light signalling effectively activates chicoric acid biosynthesis, providing a foundation for the application of blue light supplementation technology in industrial production.

Harnessing controlled-environment systems for enhanced production of medicinal plants

Medicinal plants are valued for their contributions to human health. However, the growing demand for medicinal plants and the concerns regarding their quality and sustainability have prompted the reassessment of conventional production practices. Controlled-environment cropping systems, such as vertical farms, offer a transformative approach to production of medicinal plants. By enabling precise control over environmental factors, such as light, carbon dioxide, temperature, humidity, nutrients, and airflow, controlled environments can improve the consistency, concentration, and yield of bioactive phytochemicals in medicinal plants. This review explores the potential of controlled-environment systems for enhancing production of medicinal plants. First, we describe how controlled environments can overcome the limitations of conventional production in improving the quality of medicinal plants. Next, we propose strategies based on plant physiology to manipulate environmental conditions for enhancing the levels of bioactive compounds in plants. These strategies include improving photosynthetic carbon assimilation, light spectrum signalling, purposeful stress elicitation, and chronoculture. We describe the underlying mechanisms and practical applications of these strategies. Finally, we highlight the major knowledge gaps and challenges that limit the application of controlled environments, and discuss future research directions.

Dynamic transcriptomics unveils parallel transcriptional regulation in artemisinin and phenylpropanoid biosynthesis pathways under cold stress in Artemisia annua

Cold stress, a major abiotic factor, positively modulates the synthesis of artemisinin in Artemisia annua and influences the biosynthesis of other secondary metabolites. To elucidate the changes in the synthesis of secondary metabolites under low-temperature conditions, we conducted dynamic transcriptomic and metabolite quantification analyses of A. annua leaves. The accumulation of total organic carbon (TOC) in leaves under cold stress provided ample precursors for secondary metabolite synthesis. Short-term exposure to low temperature induced a transient increase in jasmonic acid synthesis, which positively regulates the artemisinin biosynthetic pathway, contributing to artemisinin accumulation. Additionally, transcripts of genes encoding key enzymes and transcription factors in both the phenylpropanoid and artemisinin biosynthetic pathways, including PAL, C4H, ADS, and DBR2, exhibited similar expression patterns, suggesting a coordinated effect between these pathways. Prolonged exposure to low temperature sustained high levels of phenylpropanoid synthesis, leading to significant increases in lignin, flavonoids, and anthocyanin. Conversely, the final stage of the artemisinin biosynthetic pathway is inhibited under these conditions, resulting in elevated levels of dihydroartemisinic acid and artemisinic acid. Collectively, our study provides insights into the parallel transcriptional regulation of artemisinin and phenylpropanoid biosynthetic pathways in A. annua under cold stress.

bZIP transcription factor responds to changes in light quality and affects saponins synthesis in Eleutherococcus senticosus

Light quality considerably influences plant secondary metabolism, yet the precise mechanism underlying its impact on Eleutherococcus senticosus remains elusive. Comprehensive metabolomic and transcriptomic analyses revealed that varying light quality alters the biosynthesis of triterpene saponins by modulating the expression of genes involved in the process in E. senticosus. Through correlation analysis of gene expression and saponin biosynthesis, we identified four light-responsive transcription factors, namely EsbZIP1, EsbZIP2, EsbZIP4, and EsbZIP5. EsbZIP transcription factors function in the nucleus, with light quality-dependent promoter activity. Except for EsbZIP2, the other EsbZIP transcription factors exhibit transcriptional self-activation. Furthermore, EsbZIP can bind to the promoter areas of genes that encode important enzymes (EsFPS, EsSS, and EsSE) involved in triterpene saponin biosynthesis, thereby regulating their expression. Overexpression of EsbZIP resultes in significant down-regulation of most downstream target genes，which leads to a decrease in saponin content. Overall, varying light quality enhances the content of triterpene saponins by suppressing the expression of EsbZIP. This study thus elucidates the molecular mechanism by which E. senticosus adjusts triterpene saponin levels in response to changes in light quality.

Phytochrome interacting factor 3 mediates low light signaling to regulate isorhynchophylline biosynthesis in Uncaria rhynchophylla

Phytochrome interacting factors (PIFs) serve as crucial regulators in the light signal transduction pathway and also mediate light signals to regulate secondary metabolite synthesis in plants. However, the regulator role of PIFs in secondary metabolites often varies among different plants. Isorhynchophylline (IRN), an iconic secondary metabolite of Uncaria rhynchophylla, holds significant medicinal value. Low light induces the synthesis of IRN in previous research, but PIFs in U. rhynchophylla have not been studied to date. Building on this, we identified a PIF protein, UrPIF3, which possesses the typical conserved domains of the PIFs and is localized in the nucleus. Moreover, the expression level of UrPIF3 is consistently positively correlated with the expression of two key enzyme genes (UrSGD and UrSTR) in the IRN biosynthesis pathway, regardless of whether under low light or restoring light conditions. Yeast one-hybrid and dual-luciferase assays further demonstrated that UrPIF3 can directly upregulate UrSGD. Conversely, silencing UrPIF3 inhibits IRN synthesis, and significantly reduces the expression levels of UrSGD and UrSTR. In summary, our results suggest that under low light conditions, UrPIF3 can directly upregulate UrSGD and indirectly upregulate UrSTR, thereby promoting the synthesis of IRN.

The AaBBX21-AaHY5 module mediates light-regulated artemisinin biosynthesis in Artemisia annua L

The sesquiterpene lactone artemisinin is an important anti-malarial component produced by the glandular secretory trichomes of sweet wormwood (Artemisia annua L.). Light was previously shown to promote artemisinin production, but the underlying regulatory mechanism remains elusive. In this study, we demonstrate that ELONGATED HYPOCOTYL 5 (HY5), a central transcription factor in the light signaling pathway, cannot promote artemisinin biosynthesis on its own, as the binding of AaHY5 to the promoters of artemisinin biosynthetic genes failed to activate their transcription. Transcriptome analysis and yeast two-hybrid screening revealed the B-box transcription factor AaBBX21 as a potential interactor with AaHY5. AaBBX21 showed a trichome-specific expression pattern. Additionally, the AaBBX21-AaHY5 complex cooperatively activated transcription from the promoters of the downstream genes AaGSW1, AaMYB108, and AaORA, encoding positive regulators of artemisinin biosynthesis. Moreover, AaHY5 and AaBBX21 physically interacted with the A. annua E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1). In the dark, AaCOP1 decreased the accumulation of AaHY5 and AaBBX21 and repressed the activation of genes downstream of the AaHY5-AaBBX21 complex, explaining the enhanced production of artemisinin upon light exposure. Our study provides insights into the central regulatory mechanism by which light governs terpenoid biosynthesis in the plant kingdom.

Ménage à trois: light, terpenoids, and quality of plants

In controlled environment agriculture (CEA), light is used to impact terpenoid production and improve plant quality. In this review we discuss various aspects of light as important regulators of terpenoid production in different plant organs. Spectral quality primarily modifies terpenoid profiles, while intensity and photoperiod influence abundances. The central regulator of light signal transduction elongated hypocotyl 5 (HY5) controls transcriptional regulation of terpenoids under UV, red (R), and blue (B) light. The larger the fraction of R and green (G) light, the more beneficial the effect on monoterpenoid and sesquiterpenoid biosynthesis, and such an effect may depend on the presence of B light. A large fraction of R light is mostly detrimental to tetraterpenoid production. We conclude that light is a promising tool to steer terpenoid production and potentially tailor the quality of plants.

Advanced metabolic engineering strategies for increasing artemisinin yield in Artemisia annua L

Artemisinin, also known as 'Qinghaosu', is a chemically sesquiterpene lactone containing an endoperoxide bridge. Due to the high activity to kill Plasmodium parasites, artemisinin and its derivatives have continuously served as the foundation for antimalarial therapies. Natural artemisinin is unique to the traditional Chinese medicinal plant Artemisia annua L., and its content in this plant is low. This has motivated the synthesis of this bioactive compound using yeast, tobacco, and Physcomitrium patens systems. However, the artemisinin production in these heterologous hosts is low and cannot fulfil its increasing clinical demand. Therefore, A. annua plants remain the major source of this bioactive component. Recently, the transcriptional regulatory networks related to artemisinin biosynthesis and glandular trichome formation have been extensively studied in A. annua. Various strategies including (i) enhancing the metabolic flux in artemisinin biosynthetic pathway; (ii) blocking competition branch pathways; (iii) using transcription factors (TFs); (iv) increasing peltate glandular secretory trichome (GST) density; (v) applying exogenous factors; and (vi) phytohormones have been used to improve artemisinin yields. Here we summarize recent scientific advances and achievements in artemisinin metabolic engineering, and discuss prospects in the development of high-artemisinin yielding A. annua varieties. This review provides new insights into revealing the transcriptional regulatory networks of other high-value plant-derived natural compounds (e.g., taxol, vinblastine, and camptothecin), as well as glandular trichome formation. It is also helpful for the researchers who intend to promote natural compounds production in other plants species.

AaABI5 transcription factor mediates light and abscisic acid signaling to promote anti-malarial drug artemisinin biosynthesis in Artemisia annua

Artemisia annua, a member of the Asteraceae family, remains the primary source of artemisinin. However, the artemisinin content in the existing varieties of this plant is very low. In this study, we found that the environmental factors light and phytohormone abscisic acid (ABA) could synergistically promote the expression of artemisinin biosynthetic genes. Notably, the increased expression levels of those genes regulated by ABA depended on light. Gene expression analysis found that AaABI5, a transcription factor belonging to the basic leucine zipper (bZIP) family, was inducible by the light and ABA treatment. Analysis of AaABI5-overexpressing and -suppressing lines suggested that AaABI5 could enhance artemisinin biosynthesis and activate the expression of four core biosynthetic genes. In addition, the key regulator of light-induced artemisinin biosynthesis, AaHY5, could bind to the promoter of AaABI5 and activate its expression. In conclusion, our results demonstrated that AaABI5 acts as an important molecular junction for the synergistic promotion of artemisinin biosynthesis by light and ABA signals, which provides a candidate gene for developing new germplasms of high-quality A. annua.

Genome-wide characterization of regulator of chromosome condensation 1 (RCC1) gene family in Artemisia annua L. revealed a conservation evolutionary pattern

BACKGROUND

Artemisia annua is the major source for artemisinin production. The artemisinin content in A. annua is affected by different types of light especially the UV light. UVR8, a member of RCC1 gene family was found to be the UV-B receptor in plants. The gene structures, evolutionary history and expression profile of UVR8 or RCC1 genes remain undiscovered in A. annua.

RESULTS

Twenty-two RCC1 genes (AaRCC1) were identified in each haplotype genome of two diploid strains of A. annua, LQ-9 and HAN1. Varied gene structures and sequences among paralogs were observed. The divergence of most RCC1 genes occurred at 46.7 - 51 MYA which overlapped with species divergence of core Asteraceae during the Eocene, while no recent novel RCC1 members were found in A. annua genome. The number of RCC1 genes remained stable among eudicots and RCC1 genes underwent purifying selection. The expression profile of AaRCC1 is analogous to that of Arabidopsis thaliana (AtRCC1) when responding to environmental stress.

CONCLUSIONS

This study provided a comprehensive characterization of the AaRCC1 gene family and suggested that RCC1 genes were conserved in gene number, structures, constitution of amino acids and expression profiles among eudicots.

Anti-Cancer Potential of Phytochemicals: The Regulation of the Epithelial-Mesenchymal Transition

A biological process called epithelial-mesenchymal transition (EMT) allows epithelial cells to change into mesenchymal cells and acquire some cancer stem cell properties. EMT contributes significantly to the metastasis, invasion, and development of treatment resistance in cancer cells. Current research has demonstrated that phytochemicals are emerging as a potential source of safe and efficient anti-cancer medications. Phytochemicals could disrupt signaling pathways related to malignant cell metastasis and drug resistance by suppressing or reversing the EMT process. In this review, we briefly describe the pathophysiological properties and the molecular mechanisms of EMT in the progression of cancers, then summarize phytochemicals with diverse structures that could block the EMT process in different types of cancer. Hopefully, these will provide some guidance for future research on phytochemicals targeting EMT.

Towards greenhouse cultivation of Artemisia annua: The application of LEDs in regulating plant growth and secondary metabolism

Artemisinin is a sesquiterpene lactone produced in glandular trichomes of Artemisia annua, and is extensively used in the treatment of malaria. Growth and secondary metabolism of A. annua are strongly regulated by environmental conditions, causing unstable supply and quality of raw materials from field grown plants. This study aimed to bring A. annua into greenhouse cultivation and to increase artemisinin production by manipulating greenhouse light environment using LEDs. A. annua plants were grown in a greenhouse compartment for five weeks in vegetative stage with either supplemental photosynthetically active radiation (PAR) (blue, green, red or white) or supplemental radiation outside PAR wavelength (far-red, UV-B or both). The colour of supplemental PAR hardly affected plant morphology and biomass, except that supplemental green decreased plant biomass by 15% (both fresh and dry mass) compared to supplemental white. Supplemental far-red increased final plant height by 23% whereas it decreased leaf area, plant fresh and dry weight by 30%, 17% and 7%, respectively, compared to the treatment without supplemental radiation. Supplemental UV-B decreased plant leaf area and dry weight (both by 7%). Interestingly, supplemental green and UV-B increased leaf glandular trichome density by 11% and 9%, respectively. However, concentrations of artemisinin, arteannuin B, dihydroartemisinic acid and artemisinic acid only exhibited marginal differences between the light treatments. There were no interactive effects of far-red and UV-B on plant biomass, morphology, trichome density and secondary metabolite concentrations. Our results illustrate the potential of applying light treatments in greenhouse production of A. annua to increase trichome density in vegetative stage. However, the trade-off between light effects on plant growth and trichome initiation needs to be considered. Moreover, the underlying mechanisms of light spectrum regulation on artemisinin biosynthesis need further clarification to enhance artemisinin yield in greenhouse production of A. annua.

Synergistic interaction of two bHLH transcription factors positively regulates artemisinin biosynthetic pathway in Artemisia annua L

The wonder drug artemisinin, a sesquiterpene lactone endoperoxide from Artemisia annua is the million-dollar molecule required to curb the deadliest disease, Malaria. One of the major challenges even today is to increase the concentration of artemisinin within plants. The transcription factors are important regulators of plant secondary metabolites and have the potential to regulate key steps or the whole biosynthetic pathway. In this study, we have identified and characterised two bHLH transcription factors (Aa6119 and Aa7162) from A. annua. Both the transcription factors turned out to be transcriptionally active and nuclear-localised typical bHLH proteins. In our study, we found that Aa6119 specifically binds to the E-box element present on the promoter of artemisinin biosynthetic gene, AMORPHA-4,11-DIENE SYNTHASE (ADS). The protein-DNA interaction confirmed by Yeast one-hybrid assay was specific as Aa6119 was unable to bind to the mutated E-boxes of ADS. Further, Aa6119 interacted physically with Aa7162, which was confirmed in vitro by Yeast two-hybrid assay and in vivo by Bimolecular Fluorescent complementation assay. Our quantitative expression studies have confirmed that Aa6119 and Aa7162 act synergistically in the regulation of artemisinin biosynthetic and trichome developmental genes. The higher accumulation of artemisinin content in the transient co-transformed transgenic plants than in the individual over-expression transgenic plants has further validated that Aa6119 and Aa7162 act positively and synergistically to regulate artemisinin accumulation.

Red and blue light function antagonistically to regulate cadmium tolerance by modulating the photosynthesis,antioxidant defense system and Cd uptake in cucumber(Cucumis sativus L.)

Cadmium (Cd) is highly toxic to both plants and humans.Light plays crucial roles in plant growth, development and stress responses, but how light functions in plant Cd response remain unclear.Here,we found that Cd treatment significantly induced the expression of PHYB but not PHYA and CRY1 in leaves and roots of cucumber. Correspondingly,compared with white light (W) during Cd stress,red light(R) increased Cd sensitivity,whereas blue light (B) enhanced Cd tolerance as evidenced by decreased Cd-induced chlorosis, growth inhibition, photosynthesis inhibition and chloroplast ultrastructure damage.Furthermore,B markedly increased the transcripts and activities of the antioxidant enzymes including ascorbate peroxidase (APX),catalase (CAT),superoxide dismutase (SOD) and glutathione reductase (GR),as well as glutathione (GSH) content and GSH1 expression, resulting in hydrogen peroxide (H₂O₂) and superoxide (O₂^.-) reduction,but R treatment showed the opposite trend. Moreover, R and B markedly up-regulated and down-regulated the expression levels of Cd uptake and transport genes including IRT1, NRAMP1 and HMA3, leading to more and less Cd accumulation than the W-treated plants in both shoots and roots, respectively under Cd stress. Collectively, our data clearly demonstrate that R and B function antagonistically to regulate Cd tolerance in cucumber via modulating the photosynthesis, antioxidant defense system and Cd uptake, providing a novel light quality control strategy to enhance crop Cd tolerance and food safety.

Variation in terpenoids in leaves of Artemisia annua grown under different LED spectra resulting in diverse antimalarial activities against Plasmodium falciparum

BACKGROUND

Productivities of bioactive compounds in high-value herbs and medicinal plants are often compromised by uncontrollable environmental parameters. Recent advances in the development of plant factories with artificial lighting (PFAL) have led to improved qualitative and/or quantitative production of bioactive compounds in several medicinal plants. However, information concerning the effect of light qualities on plant pharmaceutical properties is limited. The influence of three different light-emitting diode (LED) spectra on leaf fresh weight (FW), bioactive compound production and bioactivity of Artemisia annua L. against the malarial parasite Plasmodium falciparum NF54 was investigated. Correlation between the A. annua metabolites and antimalarial activity of light-treated plant extracts were also determined.

RESULTS

Artemisia annua plants grown under white and blue spectra that intersected at 445 nm exhibited higher leaf FW and increased amounts of artemisinin and artemisinic acid, with enhanced production of several terpenoids displaying a variety of pharmacological activities. Conversely, the red spectrum led to diminished production of bioactive compounds and a distinct metabolite profile compared with other wavelengths. Crude extracts obtained from white and blue spectral treatments exhibited 2 times higher anti-Plasmodium falciparum activity than those subjected to the red treatment. Highest bioactivity was 4 times greater than those obtained from greenhouse-grown plants. Hierarchical cluster analysis (HCA) revealed a strong correlation between levels of several terpenoids and antimalarial activity, suggesting that these compounds might be involved in increasing antimalarial activity.

CONCLUSIONS

Results demonstrated a strategy to overcome the limitation of A. annua cultivation in Bangkok, Thailand. A specific LED spectrum that operated in a PFAL system promoted the accumulation of some useful phytochemicals in A. annua, leading to increased antimalarial activity. Therefore, the application of PFAL with appropriate light spectra showed promise as an alternative method for industrial production of A. annua or other useful medicinal plants with minimal environmental influence.

AaHY5 ChIP-seq based on transient expression system reveals the role of AaWRKY14 in artemisinin biosynthetic gene regulation

ChIP-seq (Chromatin immunoprecipitation with sequencing) is the gold standard for determining genome-wide in vivo transcription factor binding sites, the first step for targets prediction and network construction. For non-model plants, it is challenging to perform ChIP-seq due to the difficulty in generating stable transgenic plants. AaHY5 is a positive regulator in artemisinin biosynthesis, whose detailed mode of action remains elusive. Here, we established a protoplast transformation procedure for Artemisia annua by optimizing different conditions in protoplast isolation and transfection. We then performed AaHY5 ChIP-seq based on the established transient expression system. Combining RNA-seq data for various tissues, we identified four transcription factors (one MYB and three WRKY family members) in AaHY5 targets that potentially regulated artemisinin biosynthesis. The three WRKY transcription factors could be induced by light and the overexpression of AaHY5 and upregulate two artemisinin biosynthetic genes, ADS and CYP71AV1. Furthermore, AaWRKY14 showed transcriptional activation activity on artemisinin biosynthetic gene CYP71AV1. Together, AaWRKY14 was identified as a potential transcription factor linking AaHY5 and the artemisinin biosynthetic gene regulation.

Genome-Wide Analysis of Light-Regulated Alternative Splicing in Artemisia annua L

Artemisinin is currently the most effective ingredient in the treatment of malaria, which is thus of great significance to study the genetic regulation of Artemisia annua. Alternative splicing (AS) is a regulatory process that increases the complexity of transcriptome and proteome. The most common mechanism of alternative splicing (AS) in plant is intron retention (IR). However, little is known about whether the IR isoforms produced by light play roles in regulating biosynthetic pathways. In this work we would explore how the level of AS in A. annua responds to light regulation. We obtained a new dataset of AS by analyzing full-length transcripts using both Illumina- and single molecule real-time (SMRT)-based RNA-seq as well as analyzing AS on various tissues. A total of 5,854 IR isoforms were identified, with IR accounting for the highest proportion (48.48%), affirming that IR is the most common mechanism of AS. We found that the number of up-regulated IR isoforms (1534/1378, blue and red light, respectively) was more than twice that of down-regulated (636/682) after treatment of blue or red light. In the artemisinin biosynthetic pathway, 10 genes produced 16 differentially expressed IR isoforms. This work demonstrated that the differential expression of IR isoforms induced by light has the potential to regulate sesquiterpenoid biosynthesis. This study also provides high accuracy full-length transcripts, which can be a valuable genetic resource for further research of A. annua, including areas of development, breeding, and biosynthesis of active compounds.

AaWRKY9 contributes to light- and jasmonate-mediated to regulate the biosynthesis of artemisinin in Artemisia annua

Artemisinin, isolated from Artemisia annua, is recommended as the preferred drug to fight malaria. Previous research showed that jasmonate (JA)-mediated promotion of artemisinin accumulation depended on light. However, the mechanism underlying the interaction of light and JA in regulating artemisinin accumulation is still unknown. We identified a WRKY transcription factor, AaWRKY9, using transcriptome analysis. The glandular trichome-specific AaWRKY9 positively regulates artemisinin biosynthesis by directly binding to the promoters of AaDBR2 and AaGSW1. The key regulator in the light pathway AaHY5 activates the expression of AaWRKY9 by binding to its promoter. In addition, AaWRKY9 interacts with AaJAZ9, a repressor in the JA signalling pathway. AaJAZ9 represses the transcriptional activation activity of AaWRKY9 in the absence of methyl jasmonate. Notably, in the presence of methyl jasmonate, the transcriptional activation activity of AaWRKY9 is increased. Taken together, our results reveal a novel molecular mechanism underlying AaWRKY9 contributes to light-mediated and jasmonate-mediated to regulate the biosynthesis of artemisinin in A. annua. Our study provides new insights into integrating the two signalling pathways to regulate terpene biosynthesis in plants.

Effects of Light on Secondary Metabolite Biosynthesis in Medicinal Plants

Secondary metabolites (SMs) found in medicinal plants are one of main sources of drugs, cosmetics, and health products. With the increase in demand for these bioactive compounds, improving the content and yield of SMs in medicinal plants has become increasingly important. The content and distribution of SMs in medicinal plants are closely related to environmental factors, especially light. In recent years, artificial light sources have been used in controlled environments for the production and conservation of medicinal germplasm. Therefore, it is essential to elucidate how light affects the accumulation of SMs in different plant species. Here, we systematically summarize recent advances in our understanding of the regulatory roles of light quality, light intensity, and photoperiod in the biosynthesis of three main types of SMs (polyphenols, alkaloids, and terpenoids), and the underlying mechanisms. This article provides a detailed overview of the role of light signaling pathways in SM biosynthesis, which will further promote the application of artificial light sources in medicinal plant production.

Metabolomic and Transcriptomic Analyses Reveal that Blue Light Promotes Chlorogenic Acid Synthesis in Strawberry

Light-emitting diodes (LEDs) have been widely used in plant factories and agricultural facilities. Different LEDs can be designed in accordance with the light quality and intensity requirements of different plants, allowing the regulation of plant growth and development, as well as metabolic processes. Blue and red lights have significant effects on anthocyanin metabolism in strawberry fruit, but their effects on other metabolites are unknown. Here, we studied the effects of blue and red lights on the metabolism and gene expression of strawberry using metabolomics combined with transcriptomics. A total of 33 differentially expressed metabolites (DEMs) and 501 differentially expressed genes (DEGs) were isolated and identified. Among these DEMs, chlorogenic acid synthesis was upregulated by the blue light compared with the red light. Co-expression network analysis of DEMs and DEGs revealed that the expression of hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyltransferase (FvHCT), the main gene in the chlorogenic acid synthetic pathway, was induced by blue light. Using multi-omics-based approach, our results suggest that different LED lights have multiple effects on strawberry fruit, with blue light able to co-upregulate chlorogenic acid synthesis and FvHCT gene expression.

Transcriptome analyses revealed the ultraviolet B irradiation and phytohormone gibberellins coordinately promoted the accumulation of artemisinin in Artemisia annua L

Background

Artemisinin-based combination therapy has become the preferred approach for treating malaria and has successfully reduced malaria-related mortality. Currently, the main source of artemisinin is Artemisia annua L., and thus, it is of strategic importance to enhance artemisinin contents in A. annua plants. Phytohormones and illumination are known to be important external environmental factor that can have notable effects on the production of secondary metabolite. The activities of different hormones can be influenced to varying degrees by light, and thus light and hormones may jointly regulate various processes in plants. Here, we performed transcriptome and metabolome analyses revealed that ultraviolet B irradiation and phytohormone gibberellins coordinately promoted the accumulation of artemisinin in Artemisia annua.

Methods

Artemisinin analysis was performed by ultra-high performance liquid chromatography-tandem quadrupole mass spectrometry (UPLC-ESI-QqQ-MS/MS). RNA sequencing, GO and KEGG enrichment analysis were applied to analyzing the differentially expressed genes (DEGs) under ultraviolet B irradiation and gibberellins treatments. Weighted gene co-expression network (WGCNA) analyzed the genes in artemisinin‑related modules and identified candidate hub genes in these modules.

Results

In this study, we found that cross-talk between UV-B and GA induced processes leading to modifications in artemisinin accumulation. A total of 14,762 genes differentially expressed (DEGs) among different treatments were identified by transcriptome analysis. UV-B and GA treatments enhanced the accumulation of artemisinin by up-regulating the expression of the key artemisinin biosynthesis genes ADS and CYP71AV1. According to the high degree value and high expression level, a total of 84 co-expressed transcription factors were identified. Among them, MYB and NAC TFs mainly involved in regulating the biosynthesis of artemisinin. Weighted gene co-expression network analysis revealed that GA + UV in blue modules was positively correlated with artemisinin synthesis, suggesting that the candidate hub genes in these modules should be up-regulated to enhance artemisinin synthesis in response to GA + UV treatment.

Conclusion

Our study demonstrated the co-regulation of artemisinin biosynthetic pathway genes under ultraviolet B irradiation and phytohormone gibberellins treatment. The co-expression was analysis revealed that the selected MYB and NAC TFs might have regulated the artemisinin biosynthesis gene expression with ADS and CYP71AV1 genes. Weighted gene co-expression network analysis revealed that GA + UV treatment in blue modules was positively correlated with artemisinin synthesis. We established the network to distinguish candidate hub genes in blue modules might be up-regulated to enhance artemisinin synthesis in response to GA + UV treatment.

Overexpression of blue light receptor AaCRY1 improves artemisinin content in Artemisia annua L.

Artemisinin, an effective antimalarial compound, is isolated from the medicinal plant Artemisia annua L. However, because of the low content of artemisinin in A. annua, the demand of artemisinin exceeds supply. Previous studies show that the artemisinin biosynthesis is promoted by light in A. annua. Cryptochrome1 (CRY1) is involved in many processes in the light response. In this study, AaCRY1 was cloned from A. annua. Overexpressing AaCRY1 in Arabidopsis thaliana cry1 mutant resulted in blue-light-dependent short hypocotyl phenotype and short coleoptile under blue light. Yeast two-hybrid and subcellular colocalization showed that AaCRY1 interacted with AtCOP1 (ubiquitin E3 ligase CONSTITUTIVE PHOTOMORPHOGENIC1). Overexpression of AaCRY1 in transgenic A. annua increased the artemisinin content. When AaCRY1 was overexpressed in A. annua driven by the CYP71AV1 (cytochrome P450 dependent amorpha-4,11-diene 12-hydroxylase) promoter, the artemisinin content was 1.6 times higher than that of the control. Furthermore, we expressed the C terminal of AaCRY1(CCT) involved a GUS-CCT fusion protein in A. annua. The results showed that the artemisinin content was increased to 1.7- to 2.4-fold in GUS-CCT transgenic A. annua plants. These results demonstrate that overexpression of GUS-CCT is an effective strategy to increase artemisinin production in 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.

Artemisia annua L. and photoresponse: from artemisinin accumulation, volatile profile and anatomical modifications to gene expression

Blue and yellow light affected metabolism and the morphology. Blue and red promote the DOXP/MEP pathway. ADS gene expression was increased in plants cultivated under blue, promoting artemisinin content. Artemisinin-based combination therapies are the most effective treatment for highly lethal malaria. Artemisinin is produced in small quantities in the glandular trichomes of Artemisia annua L. Our aim was to evaluate the effect of light quality in A. annua cultivated in vitro under different light qualities, considering anatomical and morphological changes, the volatile composition, artemisinin content and the expression of two key enzymes for artemisinin biosynthesis. Yellow light is related to the increase in the number of glandular trichomes and this seemed to positively affect the molecular diversity in A. annua. Yellow light-stimulated glandular trichome frequency without triggered area enhancement, whereas blue light stimulated both parameters. Blue light enhanced the thickness of the leaf epidermis. The B-promoting effect was due to increased cell size and not to increased cell numbers. Green and yellow light positively influenced the volatile diversity in the plantlets. Nevertheless, blue and red light seemed to promote the DOXP/MEP pathway, while red light stimulates MVA pathway. Amorpha-4,11-diene synthase gene expression was significantly increased in plants cultivated under blue light, and not red light, promoting artemisinin content. Our results showed that light quality, more specifically blue and yellow light, positively affected secondary metabolism and the morphology of plantlets. It seemed that steps prior to the last one in the artemisinin biosynthesis pathway could be strongly influenced by blue light. Our work provides an alternative method to increase the amount of artemisinin production in A. annua without the use of transgenic plants, by the employment of blue light.

Is a blue-red light a good elicitor of phenolic compounds in the family Droseraceae? A comparative study

Plants from the family Droseraceae, especially Drosera sp. and Dionaea sp., are naturally rich in phenolic derivatives such as plumbagin, among others. Plumbagin is known both for its pharmacological significance and its protective properties against light stress. Light stress - high light intensity or/and light spectral composition - activates plants' response mechanisms including, among others, hormonal (salicylic acid, jasmonic acid) pathways and secondary metabolite (phenolic compounds, proline) pathways. Short-wavelength radiation, due to its high energy, will induce the synthesis of protective secondary metabolites, including those with pharmaceutical properties. The aim of the study was to describe and compare acclimation strategies of Drosera peltata and Dionaea muscipula to blue-red light in the context of phenolic compound accumulation, and salicylic acid, jasmonic acid and proline synthesis. For the first time, differences in the responses of D. muscipula and D. peltata to blue-red light (in the ratio 6:1) were established. In Dionaea sp., it was associated with the use of redox equivalents (in particular, plastoquinone pool) for the synthesis of primary metabolites used in the process of growth and development. In Drosera sp., a rapid adjustment of redox state led to the synthesis of secondary metabolites, constituting a reservoir of carbon skeletons and allowing for a quick defence response to stress factors. In both species, blue-red light did not induce the jasmonic acid pathway. However, the salicylic acid pathway was induced as an alternative to the phenolic compound synthesis pathway. Nevertheless, the applied blue-red light was not an effective elicitor of phenolic compounds in the plants examined.

The light-induced transcription factor FtMYB116 promotes accumulation of rutin in Fagopyrum tataricum

Tartary buckwheat (Fagopyrum tataricum) not only provides a supplement to primary grain crops in China but also has high medicinal value, by virtue of its rich content of flavonoids possessing antioxidant, anti-inflammatory, and anticancer properties. Light is an important environmental factor that can regulate the synthesis of plant secondary metabolites. In this study, we treated tartary buckwheat seedlings with different wavelengths of light and found that red and blue light could increase the content of flavonoids and the expression of genes involved in flavonoid synthesis pathways. Through coexpression analysis, we identified a new MYB transcription factor (FtMYB116) that can be induced by red and blue light. Yeast one-hybrid assays and an electrophoretic mobility shift assay showed that FtMYB116 binds directly to the promoter region of flavonoid-3'-hydroxylase (F3'H), and a transient luciferase activity assay indicated that FtMYB116 can induce F3'H expression. After transforming FtMYB116 into the hairy roots of tartary buckwheat, we observed significant increases in the content of rutin and quercetin. Collectively, our results indicate that red and blue light promote an increase in flavonoid content in tartary buckwheat seedlings; we also identified a new MYB transcription factor, FtMYB116, that promotes the accumulation of rutin via direct activation of F3'H expression.