Molecular insights into AabZIP1-mediated regulation on artemisinin biosynthesis and drought tolerance in Artemisia annua

Transcription factor StWRKY1 is involved in monoterpene biosynthesis induced by light intensity in Schizonepeta tenuifolia Briq

Menthone-type monoterpenes are the main active ingredients of Schizonepeta tenuifolia Briq. Previous studies have indicated that light intensity influences the synthesis of menthone-type monoterpenes in S. tenuifolia, but the mechanism remains unclear. WRKY transcription factors play a crucial role in plant metabolism, yet their regulatory mechanisms in S. tenuifolia are not well understood. In this study, transcriptome data of S. tenuifolia leaves under different light intensities were analyzed, identifying 57 candidate transcription factors that influence monoterpene synthesis. Among these, 7 members of the StWRKY gene family were identified and mapped onto chromosomes using bioinformatics methods. The physicochemical properties of the proteins encoded by these StWRKY genes, their gene structures, and cis-acting elements were also studied. Comparative genomics and phylogenetic analyses revealed that Sch000013479 is closely related to AaWRKY1, AtWRKY41, and AtWRKY53, and it was designated as StWRKY1. Upon silencing and overexpressing the StWRKY1 transcription factor in S. tenuifolia leaves, changes in the expression of key genes in the menthone-type monoterpene synthesis pathway were observed. Specifically, when StWRKY1 was effectively silenced, the content of (-)-pulegone significantly decreased. These results enhance our understanding of the impact of StWRKYs on monoterpene synthesis in S. tenuifolia and lay the groundwork for further exploration of the regulatory mechanisms involved in the biosynthesis of menthone-type monoterpenes.

A novel bHLH gene responsive to low nitrogen positively regulates the biosynthesis of medicinal tropane alkaloids in Atropa belladonna

Medicinal tropane alkaloids (TAs), including hyoscyamine, anisodamine and scopolamine, are essential anticholinergic drugs specifically produced in several solanaceous plants. Atropa belladonna is one of the most important medicinal plants that produces TAs. Therefore, it is necessary to cultivate new A. belladonna germplasm with the high content of TAs. Here, we found that the levels of TAs were elevated under low nitrogen (LN) condition, and identified a LN-responsive bHLH transcription factor (TF) of A. belladonna (named LNIR) regulating the biosynthesis of TAs. The expression level of LNIR was highest in secondary roots where TAs are synthesized specifically, and was significantly induced by LN. Further research revealed that LNIR directly activated the transcription of hyoscyamine 6β-hydroxylase gene (H6H) by binding to its promoter, which converts hyoscyamine into anisodamine and subsequently epoxidizes anisodamine to form scopolamine. Overexpression of LNIR upregulated the expression levels of TA biosynthesis genes and consequently led to the increased production of TAs. In summary, we functionally identified a LN-responsive bHLH gene that facilitated the development of A. belladonna with high-yield TAs under the decreased usage of nitrogen fertilizer.

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.

Strategies on biosynthesis and production of bioactive compounds in medicinal plants

Medicinal plants are a valuable source of essential medicines and herbal products for healthcare and disease therapy. Compared with chemical synthesis and extraction, the biosynthesis of natural products is a very promising alternative for the successful conservation of medicinal plants, and its rapid development will greatly facilitate the conservation and sustainable utilization of medicinal plants. Here, we summarize the advances in strategies and methods concerning the biosynthesis and production of natural products of medicinal plants. The strategies and methods mainly include genetic engineering, plant cell culture engineering, metabolic engineering, and synthetic biology based on multiple "OMICS" technologies, with paradigms for the biosynthesis of terpenoids and alkaloids. We also highlight the biosynthetic approaches and discuss progress in the production of some valuable natural products, exemplifying compounds such as vindoline (alkaloid), artemisinin and paclitaxel (terpenoids), to illustrate the power of biotechnology in medicinal plants.

Transcriptome-Based WGCNA Analysis Reveals the Mechanism of Drought Resistance Differences in Sweetpotato (Ipomoea batatas (L.) Lam.)

Sweetpotato (Ipomoea batatas (L.) Lam.) is a globally significant storage root crop, but it is highly susceptible to yield reduction under severe drought conditions. Therefore, understanding the mechanism of sweetpotato resistance to drought stress is helpful for the creation of outstanding germplasm and the selection of varieties with strong drought resistance. In this study, we conducted a comprehensive analysis of the phenotypic and physiological traits of 17 sweetpotato breeding lines and 10 varieties under drought stress through a 48 h treatment in a Hoagland culture medium containing 20% PEG6000. The results showed that the relative water content (RWC) and vine-tip fresh-weight reduction (VTFWR) in XS161819 were 1.17 and 1.14 times higher than those for the recognized drought-resistant variety Chaoshu 1. We conducted RNA-seq analysis and weighted gene co-expression network analysis (WGCNA) on two genotypes, XS161819 and 18-12-3, which exhibited significant differences in drought resistance. The transcriptome analysis revealed that the hormone signaling pathway may play a crucial role in determining the drought resistance in sweetpotato. By applying WGCNA, we identified twenty-two differential expression modules, and the midnight blue module showed a strong positive correlation with drought resistance characteristics. Moreover, twenty candidate Hub genes were identified, including g47370 (AFP2), g14296 (CDKF), and g60091 (SPBC2A9), which are potentially involved in the regulation of drought resistance in sweetpotato. These findings provide important insights into the molecular mechanisms underlying drought resistance in sweetpotato and offer valuable genetic resources for the development of drought-resistant sweetpotato varieties in the future.

Is specialized metabolite regulation specialized?

Recent technical and theoretical advances have generated an explosion in the identification of specialized metabolite pathways. In comparison, our understanding of how these pathways are regulated is relatively lagging. This and the relatively young age of specialized metabolite pathways has partly contributed to a default and common paradigm whereby specialized metabolite regulation is theorized as relatively simple with a few key transcription factors and the compounds are non-regulatory end-products. In contrast, studies into model specialized metabolites, such as glucosinolates, are beginning to identify a new understanding whereby specialized metabolites are highly integrated into the plants' core metabolic, physiological, and developmental pathways. This model includes a greatly extended compendium of transcription factors controlling the pathway, key transcription factors that co-evolve with the pathway and simultaneously control core metabolic and developmental components, and finally the compounds themselves evolve regulatory connections to integrate into the plants signaling machinery. In this review, these concepts are illustrated using studies in the glucosinolate pathway within the Brassicales. This suggests that the broader community needs to reconsider how they do or do not integrate specialized metabolism into the regulatory network of their study species.

The Light- and Jasmonic Acid-Induced AaMYB108-like Positive Regulates the Initiation of Glandular Secretory Trichome in Artemisia annua L

The plant Artemisia annua L. is famous for producing "artemisinin", which is an essential component in the treatment of malaria. The glandular secretory trichomes (GSTs) on the leaves of A. annua secrete and store artemisinin. Previous research has demonstrated that raising GST density can effectively raise artemisinin content. However, the molecular mechanism of GST initiation is not fully understood yet. In this study, we identified an MYB transcription factor, the AaMYB108-like, which is co-induced by light and jasmonic acid, and positively regulates glandular secretory trichome initiation in A. annua. Overexpression of the AaMYB108-like gene in A. annua increased GST density and enhanced the artemisinin content, whereas anti-sense of the AaMYB108-like gene resulted in the reduction in GST density and artemisinin content. Further experiments demonstrated that the AaMYB108-like gene could form a complex with AaHD8 to promote the expression of downstream AaHD1, resulting in the initiation of GST. Taken together, the AaMYB108-like gene is a positive regulator induced by light and jasmonic acid for GST initiation in A. annua.

Multilayered regulation of secondary metabolism in medicinal plants

Medicinal plants represent a huge reservoir of secondary metabolites (SMs), substances with significant pharmaceutical and industrial potential. However, obtaining secondary metabolites remains a challenge due to their low-yield accumulation in medicinal plants; moreover, these secondary metabolites are produced through tightly coordinated pathways involving many spatiotemporally and environmentally regulated steps. The first regulatory layer involves a complex network of transcription factors; a second, more recently discovered layer of complexity in the regulation of SMs is epigenetic modification, such as DNA methylation, histone modification and small RNA-based mechanisms, which can jointly or separately influence secondary metabolites by regulating gene expression. Here, we summarize the findings in the fields of genetic and epigenetic regulation with a special emphasis on SMs in medicinal plants, providing a new perspective on the multiple layers of regulation of gene expression.

Purple Rehmannnia : investigation of the activation of R2R3-MYB transcription factors involved in anthocyanin biosynthesis

Engineering anthocyanin biosynthesis in herbs could provide health-promoting foods for improving human health. Rehmannia glutinosa is a popular medicinal herb in Asia, and was a health food for the emperors of the Han Dynasty (59 B.C.). In this study, we revealed the differences in anthocyanin composition and content between three Rehmannia species. On the 250, 235 and 206 identified MYBs in the respective species, six could regulate anthocyanin biosynthesis by activating the ANTHOCYANIDIN SYNTHASE (ANS) gene expression. Permanent overexpression of the Rehmannia MYB genes in tobacco strongly promoted anthocyanin content and expression levels of NtANS and other genes. A red appearance of leaves and tubers/roots was observed, and the total anthocyanin content and the cyanidin-3-O-glucoside content were significantly higher in the lines overexpressing RgMYB41, RgMYB42 and RgMYB43 from R. glutinosa,as well as RcMYB1 and RcMYB3 in R. chingii and RhMYB1 from R. henryi plants. Knocking out of RcMYB3 by CRISPR/Cas9 gene editing resulted in the discoloration of the R. chingii corolla lobes, and decreased the content of anthocyanin. R. glutinosa overexpressing RcMYB3 displayed a distinct purple color in the whole plants, and the antioxidant activity of the transgenic plants was significantly enhanced compared to WT. These results indicate that Rehmannia MYBs can be used to engineer anthocyanin biosynthesis in herbs to improve their additional value, such as increased antioxidant contents. This article is protected by copyright. All rights reserved.

Elevation of artemisinin content by co-transformation of artemisinin biosynthetic pathway genes and trichome-specific transcription factors in Artemisia annua

Artemisinin, derived from Artemisia annua, is currently used as the first-line treatment for malaria. However, wild-type plants have a low artemisinin biosynthesis rate. Although yeast engineering and plant synthetic biology have shown promising results, plant genetic engineering is considered the most feasible strategy, but it is also constrained by the stability of progeny development. Here we constructed three independent unique overexpressing vectors harboring three mainstream artemisinin biosynthesis enzymes HMGR, FPS, and DBR2, as well as two trichomes-specific transcription factors AaHD1 and AaORA. The simultaneous co-transformation of these vectors by Agrobacterium resulted in the successful increase of the artemisinin content in T0 transgenic lines by up to 3.2-fold (2.72%) leaf dry weight compared to the control plants. We also investigated the stability of transformation in progeny T1 lines. The results indicated that the transgenic genes were successfully integrated, maintained, and overexpressed in some of the T1 progeny plants' genomes, potentially increasing the artemisinin content by up to 2.2-fold (2.51%) leaf dry weight. These results indicated that the co-overexpression of multiple enzymatic genes and transcription factors via the constructed vectors provided promising results, which could be used to achieve the ultimate goal of a steady supply of artemisinin at affordable prices around the world.

AabHLH113 integrates jasmonic acid and abscisic acid signaling to positively regulate artemisinin biosynthesis in Artemisia annua

Artemisinin, a sesquiterpene lactone isolated from Artemisia annua, is in huge market demand due to its efficient antimalarial action, especially after the COVID-19 pandemic. Many researchers have elucidated that phytohormones jasmonic acid (JA) and abscisic acid (ABA) positively regulate artemisinin biosynthesis via types of transcription factors (TFs). However, the crosstalk between JA and ABA in regulating artemisinin biosynthesis remains unclear. Here, we identified a novel ABA- and JA-induced bHLH TF, AabHLH113, which positively regulated artemisinin biosynthesis by directly binding to the promoters of artemisinin biosynthetic genes, DBR2 and ALDH1. The contents of artemisinin and dihydroartemisinic acid increased by 1.71- to 2.06-fold and 1.47- to 2.23-fold, respectively, in AabHLH1113 overexpressed A. annua, whereas they decreased by 14-36% and 26-53%, respectively, in RNAi-AabHLH113 plants. Furthermore, we demonstrated that AabZIP1 and AabHLH112, which, respectively, participate in ABA and JA signaling pathway to regulate artemisinin biosynthesis, directly bind to and activate the promoter of AabHLH113. Collectively, we revealed a complex network in which AabHLH113 plays a key interrelational role to integrate ABA- and JA-mediated regulation of artemisinin biosynthesis.

TcbZIP60 positively regulates pyrethrins biosynthesis in Tanacetum cinerariifolium

Pyrethrins, synthesized in the perennial plant Tanacetum cinerariifolium, are a class of terpene mixtures with high insecticidal activity and low human toxicity, which are widely used in plant-derived pesticides. Numerous studies have identified multiple pyrethrins biosynthesis enzymes, which can be enhanced by exogenous hormones such as methyl jasmonate (MeJA). However, the mechanism by which hormone signaling regulates pyrethrins biosynthesis and the potential involvement of certain transcription factors (TFs) remain unclear. In this study, we found that the expression level of a TF in T. cinerariifolium was significantly increased after treatment with plant hormones (MeJA, abscisic acid). Subsequent analysis identified this TF as a member of the basic region/leucine zipper (bZIP) family and was thus named TcbZIP60. TcbZIP60 was localized in the nucleus, suggesting that it is involved in the transcription process. The expression profiles of TcbZIP60 were similar to those of pyrethrins synthesis genes in different flower organs and at different flowering stages. Furthermore, TcbZIP60 could directly bind to the E-box/G-box motifs in the promoters of the pyrethrins synthesis genes TcCHS and TcAOC to activate their expression. Transient overexpression of TcbZIP60 increased the expression levels of pyrethrins biosynthesis genes, leading to the significant accumulation of pyrethrins. Silencing of TcbZIP60 significantly downregulated pyrethrins accumulation and the expression of related genes. Overall, our results reveal a novel TF, TcbZIP60, that regulates both the terpenoid and jasmonic acid pathways of pyrethrins biosynthesis in T. cinerariifolium.

Transcriptome sequencing and gas chromatography–mass spectrometry analyses provide insights into β-caryophyllene biosynthesis in Brassica campestris

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β-Caryophyllene (BCP) was detected in Brassica campestris.

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BCP content changed in cultivars during developmental stages and MeJA treatment.

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In the phylogenetic analysis, the TPSa gene subfamily was divided into four groups

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The potential regulatory and transporter network of BCP was constructed.

Sesquiterpenes are important defensive secondary metabolites and aroma components. However, limited information is available on the mechanism of sesquiterpene formation and composition in the non-heading Chinese cabbage (NHCC) leaf. Therefore, headspace solid-phase microextraction/gas chromatography–mass spectrometry (HS-SPME/GC–MS) combined with transcriptome analysis was used to study the mechanism of volatile organic compound formation. A total of 26 volatile organic compounds were identified in two NHCC cultivars ‘SZQ’ and ‘XQC’ and their F1 hybrids. Among these, sesquiterpene β-caryophyllene was identified only in ‘XQC’ and F1. Five genes encoding caryophyllene synthase were identified. The candidate β-caryophyllene synthase genes BcTPSa11 and BcTPSa21 had high expression levels only in ‘XQC’ and F1. In addition, several transcription factors of MYB-related, MYB, bHLH, and AP2/ERF families were identified by co-expression, suggesting that they regulate β-caryophyllene biosynthesis. Our results provide a molecular basis for sesquiterpene biosynthesis as well as insights into the regulatory network of β-caryophyllene in NHCC.

From Plant to Yeast-Advances in Biosynthesis of Artemisinin

Malaria is a life-threatening disease. Artemisinin-based combination therapy (ACT) is the preferred choice for malaria treatment recommended by the World Health Organization. At present, the main source of artemisinin is extracted from Artemisia annua; however, the artemisinin content in A. annua is only 0.1-1%, which cannot meet global demand. Meanwhile, the chemical synthesis of artemisinin has disadvantages such as complicated steps, high cost and low yield. Therefore, the application of the synthetic biology approach to produce artemisinin in vivo has magnificent prospects. In this review, the biosynthesis pathway of artemisinin was summarized. Then we discussed the advances in the heterologous biosynthesis of artemisinin using microorganisms (Escherichia coli and Saccharomyces cerevisiae) as chassis cells. With yeast as the cell factory, the production of artemisinin was transferred from plant to yeast. Through the optimization of the fermentation process, the yield of artemisinic acid reached 25 g/L, thereby producing the semi-synthesis of artemisinin. Moreover, we reviewed the genetic engineering in A. annua to improve the artemisinin content, which included overexpressing artemisinin biosynthesis pathway genes, blocking key genes in competitive pathways, and regulating the expression of transcription factors related to artemisinin biosynthesis. Finally, the research progress of artemisinin production in other plants (Nicotiana, Physcomitrella, etc.) was discussed. The current advances in artemisinin biosynthesis may help lay the foundation for the remarkable up-regulation of artemisinin production in A. annua through gene editing or molecular design breeding in the future.