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

NtWRKY33 involved in senescence-induced nornicotine synthesis by activating NtE4 in tobacco

Nornicotine is an undesirable alkaloid in tobacco due to its unpleasant taste and potential toxicity. The accumulation of nornicotine in tobacco leaves is related to the development of the leaves, with very low amounts present in green leaves and a dramatic increase after senescence. While it is known that the NtE4 is a key enzyme involved in nicotine to nornicotine conversion in tobacco leaves, the specific genes regulating the expression of NtE4 during leaf senescence remain unclear. In this study, we identified a WRKY transcription factor, NtWRKY33, as being involved in nornicotine accumulation during senescence. NtWRKY33 is a nuclear protein and its expression is induced by senescence. Knocking out NtWRKY33 significantly decreased nornicotine levels in senescent leaves, whereas overexpressing NtWRKY33 significantly increased nornicotine accumulation. RT-qPCR analysis demonstrated that NtWRKY33 positively regulates the expression of NtE4 without significantly affecting other key enzyme genes involved in nornicotine biosynthesis. Yeast one-hybrid (Y1H) and dual-luciferase analysis (DLA) revealed that NtWRKY33 directly promotes NtE4 expression by binding to its promoter. Therefore, NtWRKY33 is a transcription factor involved in senescence-induced nornicotine accumulation. This study provides novel insights into the molecular mechanisms by which senescence induces nornicotine formation and identifies a new target for regulating nornicotine levels.

Genome-wide identification of the eggplant jasmonate ZIM-domain (JAZ) gene family and functional characterization of SmJAZ10 in modulating chlorophyll synthesis in leaves

The jasmonate ZIM-domain (JAZ) plays a crucial role in regulating several economic traits in crops. Despite its importance, the characterization of the SmJAZ gene family in eggplant (Solanum melongena L.) has not been documented. In this study, we identified 13 SmJAZ distributed across 9 chromosomes, which were categorized into 5 subgroups based on phylogenetic analysis. Both of them possess TIFY-motif and CCT_2 domains with varying degrees of variation. Promoter cis-element analysis predicted 42 distributed cis-elements that respond to diverse signals. Gene expression analysis demonstrated that SmJAZ exhibited responsiveness to JA, ABA, NaCl, PEG, 4 °C, blue light, and UV-B treatments. Moreover, microRNA interaction predictions identified 150 potential miRNAs, among which ath-miR5021 was found to target 8 SmJAZ mRNAs. Yeast two-hybrid assays demonstrated that most of the SmJAZs were able to interact with SmMYC2 and SmNINJA and could form JAZ-JAZ complexes. Subcellular localization analysis unveiled a diverse array of intranuclear and extranuclear localization signals for SmJAZs. Overexpressing of SmJAZ10 could decrease the chlorophyll content of seedling leaves, and the transcriptome showed that genes related to chlorophyll synthesis, such as SmCHLH, SmPORA, and SmGLK2, underwent down-regulated expression. Overall, these findings serve as a valuable resource for leveraging JA signaling to enhance eggplant quality.

Glycyrrhiza, a commonly used medicinal herb: Review of species classification, pharmacology, active ingredient biosynthesis, and synthetic biology

BACKGROUND

Licorice is extensively and globally utilized as a medicinal herb and is one of the traditional Chinese herbal medicines with valuable pharmacological effects. Its therapeutic components primarily reside within its roots and rhizomes, classifying it as a tonifying herb. As more active ingredients in licorice are unearthed and characterized, licorice germplasm resources are gaining more and more recognition. However, due to the excessive exploitation of wild licorice resources, the degrading germplasm reserves fail to meet the requirements of chemical extraction and clinical application.

AIM OF REVIEW

This article presents a comprehensive review of the classification and phylogenetic relationships of species in genus Glycyrrhiza, types of active components and their pharmacological activities, licorice omics, biosynthetic pathways of active compounds in licorice, and metabolic engineering. It aims to offer a unique and comprehensive perspective on Glycyrrhiza, integrating knowledge from diverse fields to offer a comprehensive understanding of this genus. It will serve as a valuable resource and provide a solid foundation for future research and development in the molecular breeding and synthetic biology fields of Glycyrrhiza.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Licorice has an abundance of active constituents, primarily triterpenoids, flavonoids, and polysaccharides. Modern pharmacological research unveiled its multifaceted effects encompassing anti-inflammatory, analgesic, anticancer, antiviral, antioxidant, and hepatoprotective activities. Many resources of Glycyrrhiza species remain largely untapped, and multiomic studies of the Glycyrrhiza lineage are expected to facilitate new discoveries in the fields of medicine and human health. Therefore, strategies for breeding high-yield licorice plants and developing effective biosynthesis methods for bioactive compounds will provide valuable insights into resource conservation and drug development. Metabolic engineering and microorganism-based green production provide alternative strategies to improve the production efficiency of natural products.

A generalist regulator: MYB transcription factors regulate the biosynthesis of active compounds in medicinal plants

Medicinal plants are rich in a variety of secondary metabolites with therapeutic value. However, the yields of these metabolites are generally very low, making their extraction both time-consuming and labour-intensive. Transcription factor-targeted secondary metabolic engineering can efficiently regulate the biosynthesis and accumulation of secondary metabolites in medicinal plants. v-Myb avian myeloblastosis viral oncogene homolog (MYB) transcription factors are involved in regulating various morphological and developmental processes, responses to stress, and the biosynthesis of secondary metabolites in plants. This review discusses the biological functions and transcription regulation mechanisms of MYB transcription factors and summarizes research progress concerning MYB transcription factors involved in the biosynthesis of representative active components. In the transcriptional regulatory network, MYB transcription factors regulate multiple synthase genes to mediate the biosynthesis of active compounds. This work will serve as a reference for an in-depth analysis of the MYB transcription factor family in medicinal plants.

A transcription factor of SHI family AaSHI1 activates artemisinin biosynthesis genes in Artemisia annua

BACKGROUND

Transcription factors (TFs) of plant-specific SHORT INTERNODES (SHI) family play a significant role in regulating development and metabolism in plants. In Artemisia annua, various TFs from different families have been discovered to regulate the accumulation of artemisinin. However, specific members of the SHI family in A. annua (AaSHIs) have not been identified to regulate the biosynthesis of artemisinin.

RESULTS

We found five AaSHI genes (AaSHI1 to AaSHI5) in the A. annua genome. The expression levels of AaSHI1, AaSHI2, AaSHI3 and AaSHI4 genes were higher in trichomes and young leaves, also induced by light and decreased when the plants were subjected to dark treatment. The expression pattern of these four AaSHI genes was consistent with the expression pattern of four structural genes of artemisinin biosynthesis and their specific regulatory factors. Dual-luciferase reporter assays, yeast one-hybrid assays, and transient transformation in A. annua provided the evidence that AaSHI1 could directly bind to the promoters of structural genes AaADS and AaCYP71AV1, and positively regulate their expressions. This study has presented candidate genes, with AaSHI1 in particular, that can be considered for the metabolic engineering of artemisinin biosynthesis in A. annua.

CONCLUSIONS

Overall, a genome-wide analysis of the AaSHI TF family of A. annua was conducted. Five AaSHIs were identified in A. annua genome. Among the identified AaSHIs, AaSHI1 was found to be localized to the nucleus and activate the expression of structural genes of artemisinin biosynthesis including AaADS and AaCYP71AV1. These results indicated that AaSHI1 had positive roles in modulating artemisinin biosynthesis, providing candidate genes for obtaining high-quality new A. annua germplasms.

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.

Impact of Methyl Jasmonate on Terpenoid Biosynthesis and Functional Analysis of Sesquiterpene Synthesis Genes in Schizonepeta tenuifolia

This study investigates the impact of methyl jasmonate (MeJA) on the volatile oil composition of Schizonepeta tenuifolia and elucidates the function of the StTPS45 gene, a key player in terpenoid biosynthesis. The effect of different concentrations of MeJA (0, 50, 100, 200, and 300 μmol/L) on the growth of S. tenuifolia adventitious bud clusters was analyzed over a 20 d period. Using gas chromatography-mass spectrometry (GC-MS), 17 compounds were identified from the adventitious bud clusters of S. tenuifolia. Significant changes in the levels of major monoterpenes, including increased contents of (+)-limonene and (+)-menthone, were observed, particularly at higher concentrations of MeJA. Analysis of transcriptome data from three groups treated with 0, 100, and 300 μmol/L MeJA revealed significant changes in the gene expression profiles following MeJA treatment. At 100 μmol/L MeJA, most terpene synthase (TPS) genes were overexpressed. Additionally, gene expression and functional predictions suggested that StTPS45 acts as germacrene D synthase. Therefore, StTPS45 was cloned and expressed in Escherichia coli, and enzyme activity assays confirmed its function as a germacrene D synthase. Molecular docking and structural prediction of StTPS45 further suggested specific interactions with farnesyl diphosphate (FPP), aligning with its role in the terpenoid synthesis pathway. These findings provide valuable insights into the modulation of secondary metabolite pathways by jasmonate signaling and underscore the potential of genetic engineering approaches to enhance the production of specific terpenoids in medicinal plants.

Silicon and selenium alleviate cadmium toxicity in Artemisia selengensis Turcz by regulating the plant-rhizosphere

Soil cadmium (Cd) pollution has emerged as a pressing concern due to its deleterious impacts on both plant physiology and human well-being. Silicon (Si) is renowned for its ability to mitigate excessive Cd accumulation within plant cells and reduce the mobility of Cd in soil, whereas Selenium (Se) augments plant antioxidant capabilities and promotes rhizosphere microbial activity. However, research focusing on the simultaneous utilization of Si and Se to ameliorate plant Cd toxicity through multiple mechanisms within the plant-rhizosphere remains comparatively limited. This study combined hydroponic and pot experiments to investigate the effects of the combined application of Si and Se on Cd absorption and accumulation, as well as the growth and rhizosphere of A. selengensis Turcz under Cd stress. The results revealed that a strong synergistic effect was observed between both Si and Se. The combination of Si and Se significantly increased the activity and content of enzymes and non-enzyme antioxidants within A. selengensis Turcz, reduced Cd accumulation and inhibiting its translocation from roots to shoots. Moreover, Si and Se application improved the levels of reducing sugar, soluble protein, and vitamin C, while reducing nitrite content and Cd bioavailability. Furthermore, the experimental results showed that the combination of Si and Se not only increased the abundance of core rhizosphere microorganisms, but also stimulated the activity of soil enzymes, which effectively limited the migration of Cd in the soil. These findings provided valuable insights into the effective mitigation of soil Cd toxicity to plants and also the potential applications in improving plant quality and safety.

The discovery of a novel single-function intermolecular Diels-Alder enzyme for the biosynthesis of hetero-dimer lithocarpins

The deep-sea fungus Phomopsis lithocarpus FS508 produces tenellone-macrolide conjugated hetero-dimer lithocarpins A-G with anti-tumor activities. The deficiency of new intermolecular Diels-Alder (DA) enzymes hindered the development of new bioactive hetero-dimers. A novel single-function intermolecular DA enzyme, g7882, was initially discovered in this study. The deletion of g7882 led to the disappearance of lithocarpin A and an increase in precursor level . the overexpression of g7882 significantly improved lithocarpin A yield. The in vitro function of g7882DA was also confirmed by biochemical reaction using tenellone B as a substrate. Additionally, the knockout of KS modules of PKS in cluster 41 and cluster 81 (lit cluster) eliminated the production of lithocarpins, which firstly explains the biosynthetic process of hetero-dimer lithocarpins mediated by DA enzyme in FS508. Furthermore, the removal of a novel acetyltransferase GPAT in cluster 41 and the oxidoreductase, prenyltransferase in cluster81 resulted in the reduction of lithocarpin A in P. lithocarpus. The overexpression of gpat in P. lithocarpus FS508 improved the yield of lithocarpin A significantly and produced a new tenellone derivative lithocarol G. This study offers a new DA enzyme tool for the biosynthesis of novel hetero-dimer and biochemical clues for the biosynthetic logic elucidation of lithocarpins.

Genome-wide identification and expression pattern analysis of WRKY transcription factors in response to biotic and abiotic stresses in tea plants (Camellia sinensis)

Plants would encounter various biotic and abiotic stresses during the growth and development. WRKY transcription factors (TFs) as plant-specific TFs, play an important role in responding to various adverse circumstances. Despite some advances were achieved in functional studies of WRKY TFs in tea plants, systematic analysis of the involvement of CsWRKY TFs when facing cold, salt, drought stresses and pathogen and insect attack was lacked. In present study, a total of 78 CsWRKY TFs were identified following the genomic and transcript databases. The expression patterns of CsWRKYs in various organs of tea plants and the expression profiles in response to biotic and abiotic stresses were investigated by examining representative RNA-seq data. Moreover, the effects of hormone treatments (SA and MeJA) on the transcription levels of WRKY TFs were also investigated. The phylogenetic tree of CsWRKY TFs from different species indicated the functional diversity of WRKY TFs was not closely related to their protein classification. Concurrently, CsWRKY70-2 TF was identified as a positive regulator in response to drought stress. This study provided solid and valuable information, helping us better understand the functional diversity of CsWRKY TFs, and laid the foundation for further research on the function of key WRKY genes in tea plants.

Positive regulation of the Eucommia rubber biosynthesis-related gene EuFPS1 by EuWRKY30 in Eucommia ulmoides

Eucommia rubber is a secondary metabolite from Eucommia ulmoides that has attracted much attention because of its unique properties and enormous potential for application. However, the transcriptional mechanism regulating its biosynthesis has not yet been determined. Farnesyl pyrophosphate synthase is a key enzyme in the Eucommia rubber biosynthesis. In this study, the promoter of EuFPS1 was used as bait, EuWRKY30 was screened from the cDNA library of EuFPS1 via a yeast one-hybrid system. EuWRKY30 belongs to the WRKY IIa subfamily and contains a WRKY domain and a C2H2 zinc finger motif, and the expressed protein is located in the nucleus. EuWRKY30 and EuFPS1 exhibited similar tissue expression patterns, and yeast one-hybrid and dual-luciferase experiments confirmed that EuWRKY30 directly binds to the W-box element in the EuFPS1 promoter and activates its expression. Moreover, the overexpression of EuWRKY30 significantly upregulated the expression level of EuFPS1, further increasing the density of the rubber particles and Eucommia rubber content. The results of this study indicated that EuWRKY30 positively regulates EuFPS1, which plays a critical role in the synthesis of Eucommia rubber, provided a basis for further analysis of the underlying transcriptional regulatory mechanisms.

Unveiling the regulatory mechanisms of nodules development and quality formation in Panax notoginseng using multi-omics and MALDI-MSI

INTRODUCTION

Renowned for its role in traditional Chinese medicine, Panax notoginseng exhibits healing properties including bidirectional regulatory effects on hematological system diseases. However, the presence of nodular structures near the top of the main root, known as nail heads, may impact the quality of the plant's valuable roots.

OBJECTIVES

In this paper, we aim to systematically analyze nail heads to identify their potential correlation with P. notoginseng quality. Additionally, we will investigate the molecular mechanisms behind nail head development.

METHODS

Morphological characteristics and anatomical features were analyzed to determine the biological properties of nail heads. Active component analysis and MALDI mass spectrometry imaging (MALDI-MSI) were performed to determine the correlation between nail heads and P. notoginseng quality. Phytohormone quantitation, MALDI-MSI, RNA-seq, and Arabidopsis transformation were conducted to elucidate the mechanisms of nail head formation. Finally, protein-nucleic acid and protein-protein interactions were investigated to construct a transcriptional regulatory network of nodule development and quality formation.

RESULTS

Our analyses have revealed that nail heads originate from an undeveloped lateral root. The content of ginsenosides was found to be positively associated with the amount of nail heads. Ginsenoside Rb1 specifically accumulated in the cortex of nail heads, while IAA, tZR and JAs also showed highest accumulation in the nodule. RNA-seq analysis identified PnIAA14 and PnCYP735A1 as inhibitors of lateral root development. PnMYB31 and PnMYB78 were found to form binary complexes with PnbHLH31 to synergistically regulate the expression of PnIAA14, PnCYP735A1, PnSS, and PnFPS.

CONCLUSION

Our study details the major biological properties of nodular structures in P. notoginseng and outlines their impact on the quality of the herb. It was also determined that PnMYB31- and PnMYB78-PnbHLH31 regulate phytohormones and ginsenosides accumulation, further affecting plant development and quality. This research provides insights for quality evaluation and clinical applications of P. notoginseng.

Graphene enhances artemisinin production in the traditional medicinal plant Artemisia annua via dynamic physiological processes and miRNA regulation

We investigated the effects of graphene on the model herb Artemisia annua, which is renowned for producing artemisinin, a widely used pharmacological compound. Seedling growth and biomass were promoted when A. annua was cultivated with low concentrations of graphene, an effect which was attributed to a 1.4-fold increase in nitrogen uptake, a 15%-22% increase in chlorophyll fluorescence, and greater abundance of carbon cycling-related bacteria. Exposure to 10 or 20 mg/L graphene resulted in a ∼60% increase in H2O2, and graphene could act as a catalyst accelerator, leading to a 9-fold increase in catalase (CAT) activity in vitro and thereby maintaining reactive oxygen species (ROS) homeostasis. Importantly, graphene exposure led to an 80% increase in the density of glandular secreting trichomes (GSTs), in which artemisinin is biosynthesized and stored. This contributed to a 5% increase in artemisinin content in mature leaves. Interestingly, expression of miR828 was reduced by both graphene and H2O2 treatments, resulting in induction of its target gene AaMYB17, a positive regulator of GST initiation. Subsequent molecular and genetic assays showed that graphene-induced H2O2 inhibits micro-RNA (miRNA) biogenesis through Dicers and regulates the miR828-AaMYB17 module, thus affecting GST density. Our results suggest that graphene may contribute to yield improvement in A. annua via dynamic physiological processes together with miRNA regulation, and it may thus represent a new cultivation strategy for increasing yield capacity through nanobiotechnology.

Molecular regulation of the key specialized metabolism pathways in medicinal plants

The basis of modern pharmacology is the human ability to exploit the production of specialized metabolites from medical plants, for example, terpenoids, alkaloids, and phenolic acids. However, in most cases, the availability of these valuable compounds is limited by cellular or organelle barriers or spatio-temporal accumulation patterns within different plant tissues. Transcription factors (TFs) regulate biosynthesis of these specialized metabolites by tightly controlling the expression of biosynthetic genes. Cutting-edge technologies and/or combining multiple strategies and approaches have been applied to elucidate the role of TFs. In this review, we focus on recent progress in the transcription regulation mechanism of representative high-value products and describe the transcriptional regulatory network, and future perspectives are discussed, which will help develop high-yield plant resources.

Alcohol dehydrogenases regulated by a MYB44 transcription factor underlie Lauraceae citral biosynthesis

Lineage-specific terpenoids have arisen throughout the evolution of land plants and are believed to play a role in interactions between plants and the environment. Species-specific gene clusters in plants have provided insight on the evolution of secondary metabolism. Lauraceae is an ecologically important plant family whose members are also of considerable economic value given their monoterpene contents. However, the gene cluster responsible for the biosynthesis of monoterpenes remains yet to be elucidated. Here, a Lauraceae-specific citral biosynthetic gene cluster (CGC) was identified and investigated using a multifaceted approach that combined phylogenetic, collinearity, and biochemical analyses. The CGC comprises MYB44 as a regulator and 2 alcohol dehydrogenases (ADHs) as modifying enzymes, which derived from species-specific tandem and proximal duplication events. Activity and substrate divergence of the ADHs has resulted in the fruit of mountain pepper (Litsea cubeba), a core Lauraceae species, consisting of more than 80% citral. In addition, MYB44 negatively regulates citral biosynthesis by directly binding to the promoters of the ADH-encoding genes. The aggregation of citral biosynthetic pathways suggests that they may form the basis of important characteristics that enhance adaptability. The findings of this study provide insights into the evolution of and the regulatory mechanisms involved in plant terpene biosynthesis.

The GmSTF1/2-GmBBX4 negative feedback loop acts downstream of blue-light photoreceptors to regulate isoflavonoid biosynthesis in soybean

Isoflavonoids, secondary metabolites derived from the phenylalanine pathway, are predominantly biosynthesized in legumes, especially soybean (Glycine max). They are not only essential for plant responses to biotic and abiotic stresses but also beneficial to human health. In this study, we report that light signaling controls isoflavonoid biosynthesis in soybean. Blue-light photoreceptors (GmCRY1s, GmCRY2s, GmPHOT1s, and GmPHOT2s) and the transcription factors GmSTF1 and GmSTF2 promote isoflavonoid accumulation, whereas the E3 ubiquitin ligase GmCOP1b negatively regulates isoflavonoid biosynthesis. GmPHOT1s and GmPHOT2s stabilize GmSTF1/2, whereas GmCOP1b promotes the degradation of these two proteins in soybean. GmSTF1/2 regulate the expression of approximately 27.9% of the genes involved in soybean isoflavonoid biosynthesis, including GmPAL2.1, GmPAL2.3, and GmUGT2. They also repress the expression of GmBBX4, a negative regulator of isoflavonoid biosynthesis in soybean. In addition, GmBBX4 physically interacts with GmSTF1 and GmSTF2 to inhibit their transcriptional activation activity toward target genes related to isoflavonoid biosynthesis. Thus, GmSTF1/2 and GmBBX4 form a negative feedback loop that acts downstream of photoreceptors in the regulation of isoflavonoid biosynthesis. Our study provides novel insights into the control of isoflavonoid biosynthesis by light signaling in soybean and will contribute to the breeding of soybean cultivars with high isoflavonoid content through genetic and metabolic engineering.

Comprehensive analysis of JAZ family members in Ginkgo biloba reveals the regulatory role of the GbCOI1/GbJAZs/GbMYC2 module in ginkgolide biosynthesis

Ginkgo biloba L., an ancient relict plant known as a 'living fossil', has a high medicinal and nutritional value in its kernels and leaves. Ginkgolides are unique diterpene lactone compounds in G. biloba, with favorable therapeutic effects on cardiovascular and cerebrovascular diseases. Thus, it is essential to study the biosynthesis and regulatory mechanism of ginkgolide, which will contribute to quality improvement and medication requirements. In this study, the regulatory roles of the JAZ gene family and GbCOI1/GbJAZs/GbMYC2 module in ginkgolide biosynthesis were explored based on genome and methyl jasmonate-induced transcriptome. Firstly, 18 JAZ proteins were identified from G. biloba, and the gene characteristics and expansion patterns along with evolutionary relationships of these GbJAZs were analyzed systematically. Expression patterns analysis indicated that most GbJAZs expressed highly in the fibrous root and were induced significantly by methyl jasmonate. Mechanistically, yeast two-hybrid assays suggested that GbJAZ3/11 interacted with both GbMYC2 and GbCOI1, and several GbJAZ proteins could form homodimers or heterodimers between the GbJAZ family. Moreover, GbMYC2 is directly bound to the G-box element in the promoter of GbLPS, to regulate the biosynthesis of ginkgolide. Collectively, these results systematically characterized the JAZ gene family in G. biloba and demonstrated that the GbCOI1/GbJAZs/GbMYC2 module could regulate ginkgolides biosynthesis, which provides a novel insight for studying the mechanism of JA regulating ginkgolide biosynthesis.

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.

AaABCG20 transporter involved in cutin and wax secretion affects the initiation and development of glandular trichomes in Artemisia annua

Glandular trichomes are specialized structures found on the surface of plants to produce specific compounds, including terpenes, alkaloids, and other organic substances. Artemisia annua, commonly known as sweet wormwood, synthesizes and stores the antimalarial drug artemisinin in glandular trichomes. Previous research indicated that increasing the glandular trichome density could enhance artemisinin production, and the cuticle synthesis affected the initiation and development of glandular trichomes in A. annua. In this study, AaABCG12 and AaABCG20 were isolated from A. annua that exhibited similar expression patterns to artemisinin biosynthetic genes. Of the two, AaABCG20 acted as a specific transporter in glandular trichomes. Downregulating the expression of AaABCG20 resulted in a notable reduction in the density of glandular trichome, while overexpressing AaABCG20 resulted in an increase in glandular trichome density. GC-MS analysis demonstrated that AaABCG20 was responsible for the transport of cutin and wax in A. annua. These findings indicated that AaABCG20 influenced the initiation and development of glandular trichomes through transporting cutin and wax in A. annua. This glandular trichome specific half-size ABCG-type transporter is crucial in facilitating the transportation of cutin and wax components, ultimately contributing to the successful initiation and development of glandular trichomes.

Eggplant transcription factor SmMYB5 integrates jasmonate and light signaling during anthocyanin biosynthesis

Low light conditions severely suppress anthocyanin synthesis in fruit skins, leading to compromised fruit quality in eggplant (Solanum melongena L.) production. In this study, we found that exogenous methyl-jasmonate (MeJA) application can effectively rescue the poor coloration of the eggplant pericarp under low light conditions. However, the regulatory relationship between jasmonate and light signaling for regulating anthocyanin synthesis remains unclear. Here, we identified a JA response factor, SmMYB5, as an anthocyanin positive regulator by applying RNA-sequencing and characterization of transgenic plants. Firstly, we resolved that SmMYB5 can interact with TRANSPARENT TESTA8 (SmTT8), an anthocyanin-promoted BASIC HELIX-LOOP-HELIX (bHLH) transcription factor, to form the SmMYB5-SmTT8 complex and activate CHALCONE SYNTHASE (SmCHS), FLAVANONE-3-HYDROXYLASE (SmF3H), and ANTHOCYANIN SYNTHASE (SmANS) promoters by direct binding. Secondly, we revealed that JA signaling repressors JASMONATE ZIM DOMAIN5 (SmJAZ5) and SmJAZ10 can interfere with the stability and transcriptional activity of SmMYB5-SmTT8 by interacting with SmMYB5. JA can partially rescue the transcriptional activation of SmF3H and SmANS promoters by inducing SmJAZ5/10 degradation. Thirdly, we demonstrated that the protein abundance of SmMYB5 is regulated by light. CONSTITUTIVELY PHOTOMORPHOGENIC1 (SmCOP1) interacts with SmMYB5 to trigger SmMYB5 degradation via the 26S proteasome pathway. Finally, we delineated a light-dependent JA-SmMYB5 signaling pathway that promotes anthocyanin synthesis in eggplant fruit skins. These results provide insights into the mechanism of the integration of JA and light signals in regulating secondary metabolite synthesis in plants.

Genomic characterization of WRKY transcription factors related to secoiridoid biosynthesis in Gentiana macrophylla

Gentiana macrophylla is one of Chinese herbal medicines in which 4 kinds of iridoids or secoiridoids, such as loganic acid, sweroside, swertiamarin, and gentiopicroside, are identified as the dominant medicinal secondary metabolites. WRKY, as a large family of transcription factors (TFs), plays an important role in the synthesis of secondary metabolites in plants. Therefore, WRKY genes involved in the biosynthesis of secoiridoids in G. macrophylla were systematically studied. First, a comprehensive genome-wide analysis was performed, and 42 GmWRKY genes were identified, which were unevenly distributed in 12 chromosomes. Accordingly, gene structure, collinearity, sequence alignment, phylogenetic, conserved motif and promoter analyses were performed, and the GmWRKY proteins were divided into three subfamilies based on phylogenetic and multiple sequence alignment analyses. Moreover, the enzyme-encoding genes of the secoiridoid biosynthesis pathway and their promoters were then analysed, and the contents of the four secoiridoids were determined in different tissues. Accordingly, correlation analysis was performed using Pearson's correlation coefficient to construct WRKY gene-enzyme-encoding genes and WRKY gene-metabolite networks. Meanwhile, G. macrophylla seedlings were treated with methyl jasmonate (MeJA) to detect the dynamic change trend of GmWRKYs, biosynthetic genes, and medicinal ingredient accumulation. Thus, a total of 12 GmWRKYs were identified to be involved in the biosynthesis of secoiridoids, of which 8 (GmWRKY1, 6, 12, 17, 33, 34, 38 and 39) were found to regulate the synthesis of gentiopicroside, and 4 (GmWRKY7, 14, 26 and 41) were found to regulate the synthesis of loganic acid. Taken together, this study systematically identified WRKY transcription factors related to the biosynthesis of secoiridoids in G. macrophylla, which could be used as a cue for further investigation of WRKY gene functions in secondary metabolite accumulation.

PatWRKY71 transcription factor regulates patchoulol biosynthesis and plant defense response

Patchoulol, a valuable compound belonging to the sesquiterpenoid family, is the primary component of patchouli oil produced by Pogostemon cablin (P. cablin). It has a variety of pharmacological and biological activities and is widely used in the medical and cosmetic industries. However, despite its significance, there is a lack of research on the transcriptional modulation of patchoulol biosynthesis.Salicylic acid (SA), is a vital plant hormone that serves as a critical signal molecule and plays an essential role in plant growth and defense. However, to date, no studies have explored the modulation of patchoulol biosynthesis by SA. In our study, we discovered that the application of SA can enhance the production of patchoulol. Utilizing transcriptome analysis of SA-treated P. cablin, we identified a crucial downstream transcription factor, PatWRKY71. The transcription level of PatWRKY71 was significantly increased with the use of SA. Furthermore, our research has revealed that PatWRKY71 was capable of binding to the promoter of PatPTS, ultimately leading to an increase in its expression. When PatWRKY71 was silenced by a virus, the expression of both PatWRKY71 and PatPTS was reduced, resulting in the down-regulation of patchoulol production. Through our studies, we discovered that heterologous expression of PatWRKY71 leads to an increase in the sensitivity of Arabidopsis to salt and Cd, as well as an outbreak of reactive oxygen species (ROS). Additionally, we uncovered the regulatory role of PatWRKY71 in both patchoulol biosynthesis and plant defense response. This discovery provided a theoretical basis for the improvement of the content of patchoulol and the resistance of P. cablin through genetic engineering.

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.

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.

LcMYB106 suppresses monoterpene biosynthesis by negatively regulating LcTPS32 expression in Litsea cubeba

Litsea cubeba, the core species of the Lauraceae family, is valuable for the production of essential oils due to its high concentration of monoterpenes (90%). The key monoterpene synthase and metabolic regulatory network of monoterpene biosynthesis have provided new insights for improving essential oil content. However, there are few studies on the regulation mechanism of monoterpenes in L. cubeba. In this study, we investigated LcTPS32, a member of the TPS-b subfamily, and identified its function as an enzyme for the synthesis of monoterpenes, including geraniol, α-pinene, β-pinene, β-myrcene, linalool and eucalyptol. The quantitative real-time PCR analysis showed that LcTPS32 was highly expressed in the fruits of L. cubeba and contributed to the characteristic flavor of its essential oil. Overexpression of LcTPS32 resulted in a significant increase in the production of monoterpenes in L. cubeba by activating both the MVA and MEP pathways. Additionally, the study revealed that LcMYB106 played a negative regulatory role in monoterpenes biosynthesis by directly binding to the promoter of LcTPS32. Our study indicates that LcMYB106 could serve as a crucial target for metabolic engineering endeavors, aiming at enhancing the monoterpene biosynthesis in L. cubeba.

WRKY transcription factors in Arachis hypogaea and its donors: From identification to function prediction

WRKY transcription factors (TFs) play important roles in plant growth and development and responses to abiotic and biotic stresses. Since the initial isolation of a WRKY TF in Ipomoea batatas in 1994, WRKY TFs have been identified in plants, protozoa, and fungi. Peanut (Arachis hypogaea) is a key oil and protein crop for humans and a forage source for animal consumption. Several Arachis genomes have been sequenced and genome-wide WRKY TFs have been identified. In this review, we summarized WRKY TFs and their functions in A. hypogaea and its donors. We also standardized the nomenclature for Arachis WRKY TFs to ensure uniformity. We determined the evolutionary relationships between Arachis and Arabidopsis thaliana WRKY (AtWRKY) TFs using a phylogenetic analysis. Biological functions and regulatory networks of Arachis WRKY TFs were predicted using AtWRKY TFs. Thus, this review paves the way for studies of Arachis WRKY TFs.

The endomembrane system: how does it contribute to plant secondary metabolism?

New organelle acquisition through neofunctionalization of the endomembrane system (ES) with respect to plant secondary metabolism is a key evolutionary strategy for plant adaptation, which is overlooked due to the complexity of angiosperms. Bryophytes produce a broad range of plant secondary metabolites (PSMs), and their simple cellular structures, including unique organelles, such as oil bodies (OBs), highlight them as suitable model to investigate the contribution of the ES to PSMs. In this opinion, we review latest findings on the contribution of the ES to PSM biosynthesis, with a specific focus on OBs, and propose that the ES provides organelles and trafficking routes for PSM biosynthesis, transportation, and storage. Therefore, future research on ES-derived organelles and trafficking routes will provide essential knowledge for synthetic applications.

Light regulation of the biosynthesis of phenolics, terpenoids, and alkaloids in plants

Biosynthesis of specialized metabolites (SM), including phenolics, terpenoids, and alkaloids, is stimulated by many environmental factors including light. In recent years, significant progress has been made in understanding the regulatory mechanisms involved in light-stimulated SM biosynthesis at the transcriptional, posttranscriptional, and posttranslational levels of regulation. While several excellent recent reviews have primarily focused on the impacts of general environmental factors, including light, on biosynthesis of an individual class of SM, here we highlight the regulation of three major SM biosynthesis pathways by light-responsive gene expression, microRNA regulation, and posttranslational modification of regulatory proteins. In addition, we present our future perspectives on this topic.

Unlocking secrets of nature's chemists: Potential of CRISPR/Cas-based tools in plant metabolic engineering for customized nutraceutical and medicinal profiles

Plant species have evolved diverse metabolic pathways to effectively respond to internal and external signals throughout their life cycle, allowing adaptation to their sessile and phototropic nature. These pathways selectively activate specific metabolic processes, producing plant secondary metabolites (PSMs) governed by genetic and environmental factors. Humans have utilized PSM-enriched plant sources for millennia in medicine and nutraceuticals. Recent technological advances have significantly contributed to discovering metabolic pathways and related genes involved in the biosynthesis of specific PSM in different food crops and medicinal plants. Consequently, there is a growing demand for plant materials rich in nutrients and bioactive compounds, marketed as "superfoods". To meet the industrial demand for superfoods and therapeutic PSMs, modern methods such as system biology, omics, synthetic biology, and genome editing (GE) play a crucial role in identifying the molecular players, limiting steps, and regulatory circuitry involved in PSM production. Among these methods, clustered regularly interspaced short palindromic repeats-CRISPR associated protein (CRISPR/Cas) is the most widely used system for plant GE due to its simple design, flexibility, precision, and multiplexing capabilities. Utilizing the CRISPR-based toolbox for metabolic engineering (ME) offers an ideal solution for developing plants with tailored preventive (nutraceuticals) and curative (therapeutic) metabolic profiles in an ecofriendly way. This review discusses recent advances in understanding the multifactorial regulation of metabolic pathways, the application of CRISPR-based tools for plant ME, and the potential research areas for enhancing plant metabolic profiles.

AaWRKY6 contributes to artemisinin accumulation during growth in Artemisia annua

Artemisinin, which is extracted from the plant Artemisia annua L., is a crucial drug for curing malaria and has potential applications for treating cancer, diabetes, pulmonary tuberculosis, and other conditions. Demand for artemisinin is therefore high, and enhancing its yield is important. Artemisinin dynamics change during the growth cycle of A. annua; however, the regulatory networks underlying these changes are poorly understood. Here, we collected A. annua leaves at different growth stages and identified target genes from transcriptome data. We determined that WRKY6 binds to the promoters of the artemisinin biosynthesis gene artemisinic aldehyde Δ11(13) reductase (DBR2). In agreement, overexpression of WRKY6 in A. annua resulted in higher expression levels of genes in the artemisinin biosynthesis pathway and greater artemisinin contents than in the wild type. When expression of WRKY6 was down-regulated, artemisinin biosynthesis pathway genes were also down-regulated and the content of artemisinin was lower. WRKY6 mediates the transcriptional activation of artemisinin biosynthesis by binding to the promoter of DBR2, making it a key regulator for modulating the dynamics of artemisinin changes during the A. annua growth cycle.

Review: WRKY transcription factors: Understanding the functional divergence

WRKY transcription factors (TFs) play crucial roles in the growth and development of plants and their response to environmental changes. WRKY TFs have been detected in sequenced plant genomes. The functions and regulatory networks of many WRKY TFs, especially from Arabidopsis thaliana (AtWRKY TFs), have been revealed, and the origin of WRKY TFs in plants is clear. Nonetheless, the relationship between WRKY TFs function and classification is unclear. Furthermore, the functional divergence of homologous WRKY TFs in plants is unclear. In this review, WRKY TFs were explored based on WRKY-related literature published from 1994 to 2022. WRKY TFs were identified in 234 species at the genome and transcriptome levels. The biological functions of ∼ 71 % of AtWRKY TFs were uncovered. Although functional divergence occurred in homologous WRKY TFs, different WRKY TF groups had no preferential function.

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.

High light triggers flavonoid and polysaccharide synthesis through DoHY5-dependent signaling in Dendrobium officinale

Dendrobium officinale is edible and has medicinal and ornamental functions. Polysaccharides and flavonoids, including anthocyanins, are important components of D. officinale that largely determine the nutritional quality and consumer appeal. There is a need to study the molecular mechanisms regulating anthocyanin and polysaccharide biosynthesis to enhance D. officinale quality and its market value. Here, we report that high light (HL) induced the accumulation of polysaccharides, particularly mannose, as well as anthocyanin accumulation, resulting in red stems. Metabolome and transcriptome analyses revealed that most of the flavonoids showed large changes in abundance, and flavonoid and polysaccharide biosynthesis was significantly activated under HL treatment. Interestingly, DoHY5 expression was also highly induced. Biochemical analyses demonstrated that DoHY5 directly binds to the promoters of DoF3H1 (involved in anthocyanin biosynthesis), DoGMPP2, and DoPMT28 (involved in polysaccharide biosynthesis) to activate their expression, thereby promoting anthocyanin and polysaccharide accumulation in D. officinale stems. DoHY5 silencing decreased flavonoid- and polysaccharide-related gene expression and reduced anthocyanin and polysaccharide accumulation, whereas DoHY5 overexpression had the opposite effects. Notably, naturally occurring red-stemmed D. officinale plants similarly have high levels of anthocyanin and polysaccharide accumulation and biosynthesis gene expression. Our results reveal a previously undiscovered role of DoHY5 in co-regulating anthocyanin and polysaccharide biosynthesis under HL conditions, improving our understanding of the mechanisms regulating stem color and determining nutritional quality in D. officinale. Collectively, our results propose a robust and simple strategy for significantly increasing anthocyanin and polysaccharide levels and subsequently improving the nutritional quality of D. officinale.

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.

Piriformospora indica alter root-associated microbiome structure to enhance Artemisia annua L. tolerance to arsenic

Microorganisms in the rhizosphere are crucial allies for plant stress tolerance. Recent research suggests that by interacting with the rhizosphere microbiome, microorganisms can aid in the revegetation of soils contaminated with heavy metal(loid)s (HMs). However, it is unknown that how Piriformospora indica influences the rhizosphere microbiome to mitigate arsenic-toxicity in arsenic-enriched environments. Artemisia annua plants were grown in the presence or absence of P. indica and spiked with low (50) and high (150 µmol/L) concentrations of arsenic (As). After inoculation with P. indica, fresh weight increased by 37.7% and 10% in control and high concentration treated plants, respectively. Transmission electron microscopy showed that cellular organelles were severely damaged by As and even disappeared under high concentration. Furthermore, As was mostly accumulated by 5.9 and 18.1 mg/kg dry weight in the roots of inoculated plants treated with low and high concentrations of As, respectively. Additionally, 16 S and ITS rRNA gene sequencing were applied to analyze the rhizosphere microbial community structure of A. annua under different treatments. A significant difference was observed in microbial community structure under different treatments as revealed by non-metric multidimensional scaling ordination. The bacterial and fungal richness and diversity in the rhizosphere of inoculated plants were actively balanced and regulated by P. indica co-cultivation. Lysobacter and Steroidobacter were found to be the As-resistant bacterial genera. We conclude that P. indica inoculation could alter rhizosphere microecology, thereby mitigating As-toxicity without harming the environment.

AaSEPALLATA1 integrates jasmonate and light-regulated glandular secretory trichome initiation in Artemisia annua

Glandular secretory trichomes (GSTs) can secrete and store a variety of specific metabolites. By increasing GST density, valuable metabolites can be enhanced in terms of productivity. However, the comprehensive and detailed regulatory network of GST initiation still needs further investigation. By screening a complementary DNA library derived from young leaves of Artemisia annua, we identified a MADS-box transcription factor, AaSEPALLATA1 (AaSEP1), that positively regulates GST initiation. Overexpression of AaSEP1 in A. annua substantially increased GST density and artemisinin content. The HOMEODOMAIN PROTEIN 1 (AaHD1)-AaMYB16 regulatory network regulates GST initiation via the jasmonate (JA) signaling pathway. In this study, AaSEP1 enhanced the function of AaHD1 activation on downstream GST initiation gene GLANDULAR TRICHOME-SPECIFIC WRKY 2 (AaGSW2) through interaction with AaMYB16. Moreover, AaSEP1 interacted with the JA ZIM-domain 8 (AaJAZ8) and served as an important factor in JA-mediated GST initiation. We also found that AaSEP1 interacted with CONSTITUTIVE PHOTOMORPHOGENIC 1 (AaCOP1), a major repressor of light signaling. In this study, we identified a MADS-box transcription factor that is induced by JA and light signaling and that promotes the initiation of GST in A. annua.

Trichome-Specific Analysis and Weighted Gene Co-Expression Correlation Network Analysis (WGCNA) Reveal Potential Regulation Mechanism of Artemisinin Biosynthesis in Artemisia annua

Trichomes are attractive cells for terpenoid biosynthesis and accumulation in Artemisia annua. However, the molecular process underlying the trichome of A. annua is not yet fully elucidated. In this study, an analysis of multi-tissue transcriptome data was performed to examine trichome-specific expression patterns. A total of 6646 genes were screened and highly expressed in trichomes, including artemisinin biosynthetic genes such as amorpha-4,11-diene synthase (ADS) and cytochrome P450 monooxygenase (CYP71AV1). Mapman and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis showed that trichome-specific genes were mainly enriched in lipid metabolism and terpenoid metabolism. These trichome-specific genes were analyzed by a weighted gene co-expression network analysis (WGCNA), and the blue module linked to terpenoid backbone biosynthesis was determined. Hub genes correlated with the artemisinin biosynthetic genes were selected based on TOM value. ORA, Benzoate carboxyl methyltransferase (BAMT), Lysine histidine transporter-like 8 (AATL1), Ubiquitin-like protease 1 (Ulp1) and TUBBY were revealed as key hub genes induced by methyl jasmonate (MeJA) for regulating artemisinin biosynthesis. In summary, the identified trichome-specific genes, modules, pathways and hub genes provide clues and shed light on the potential regulatory mechanisms of artemisinin biosynthesis in trichomes in A. annua.

JA-regulated AaGSW1-AaYABBY5/AaWRKY9 complex regulates artemisinin biosynthesis in Artemisia annua

Artemisinin, a sesquiterpene lactone from A. annua, is an essential therapeutic against malaria. YABBY family transcription factor; AaYABBY5 is an activator of AaCYP71AV1 (cytochrome P450-dependent hydroxylase) and AaDBR2 (double bond reductase 2); however, the protein-protein interactions of AaYABBY5, as well as the mechanism of its regulation, are not elucidated before. AaWRKY9 protein is a positive regulator of artemisinin biosynthesis that activates AaGSW1 (Glandular trichome specific WRKY1) and AaDBR2 (double bond reductase 2), respectively. In this study, YABBY-WRKY interactions are revealed to indirectly regulate artemisinin production. AaYABBY5 significantly increased the activity of the luciferase (LUC) gene fused to the promoter of AaGSW1. Towards the molecular basis of this regulation, AaYABBY5 interaction with AaWRKY9 protein was found. The combined effectors AaYABBY5 + AaWRKY9 showed synergistic effects toward the activities of AaGSW1, and AaDBR2 promoters, respectively. In AaYABBY5 over-expression plants, the expression of GSW1 was found significantly increase when compared to that of AaYABBY5 antisense or control plants. Secondly, AaGSW1 was seen as an upstream activator of AaYABBY5. Thirdly, it was found that AaJAZ8, a transcriptional repressor of jasmonates signaling, interacted with AaYABBY5 and attenuated its activity. Co-expression of AaYABBY5 and antiAaJAZ8 in A. annua increased the activity of AaYABBY5 towards artemisinin biosynthesis. For the first time, the current study provided the molecular basis of regulation of artemisinin biosynthesis through YABBY-WRKY interactions and its regulation through AaJAZ8. This knowledge provides AaYABBY5 overexpression plants as a powerful genetic resource for artemisinin biosynthesis.

LcWRKY17, a WRKY Transcription Factor from Litsea cubeba, Effectively Promotes Monoterpene Synthesis

The WRKY gene family is one of the most significant transcription factor (TF) families in higher plants and participates in many secondary metabolic processes in plants. Litsea cubeba (Lour.) Person is an important woody oil plant that is high in terpenoids. However, no studies have been conducted to investigate the WRKY TFs that regulate the synthesis of terpene in L. cubeba. This paper provides a comprehensive genomic analysis of the LcWRKYs. In the L. cubeba genome, 64 LcWRKY genes were discovered. According to a comparative phylogenetic study with Arabidopsis thaliana, these L. cubeba WRKYs were divided into three groups. Some LcWRKY genes may have arisen from gene duplication, but the majority of LcWRKY evolution has been driven by segmental duplication events. Based on transcriptome data, a consistent expression pattern of LcWRKY17 and terpene synthase LcTPS42 was found at different stages of L. cubeba fruit development. Furthermore, the function of LcWRKY17 was verified by subcellular localization and transient overexpression, and overexpression of LcWRKY17 promotes monoterpene synthesis. Meanwhile, dual-Luciferase and yeast one-hybrid (Y1H) experiments showed that the LcWRKY17 transcription factor binds to W-box motifs of LcTPS42 and enhances its transcription. In conclusion, this research provided a fundamental framework for future functional analysis of the WRKY gene families, as well as breeding improvement and the regulation of secondary metabolism in L. cubeba.

Transcriptional regulatory network of high-value active ingredients in medicinal plants

High-value active ingredients in medicinal plants have attracted research attention because of their benefits for human health, such as the antimalarial artemisinin, anticardiovascular disease tanshinones, and anticancer Taxol and vinblastine. Here, we review how hormones and environmental factors promote the accumulation of active ingredients, thereby providing a strategy to produce high-value drugs at a low cost. Focusing on major hormone signaling events and environmental factors, we review the transcriptional regulatory network mediating biosynthesis of representative active ingredients. In this network, many transcription factors (TFs) simultaneously control multiple synthase genes; thus, understanding the molecular mechanisms affecting transcriptional regulation of active ingredients will be crucial to developing new breeding possibilities.

LcERF134 increases the production of monoterpenes by activating the terpene biosynthesis pathway in Litsea cubeba

Litsea cubeba, an aromatic species of the Lauraceae family, produces a diverse array of monoterpenes. The biosynthesis of monoterpenes is regulated by transcriptional factors (TFs), such as APETALA2/ethylene response factor (AP2/ERF). However, the regulatory mechanisms that control the AP2/ERF gene responsible for the biosynthesis of monoterpenes in L. cubeba have yet to be elucidated. Here, we identified an AP2/ERF gene, LcERF134, as an activator for the accumulation of citral and other monoterpenes. The expression level of LcERF134 was consistent with terpene synthase LcTPS42 in the pericarp. The transient overexpression of LcERF134 significantly increased monoterpene production in L. cubeba as well as the expression of rate-limiting genes involved in the monoterpene biosynthesis pathway. Furthermore, yeast one-hybrid, dual-luciferase and electrophoretic mobility shift assays demonstrated that LcERF134 activated the monoterpene biosynthesis pathway by directly binding to the GCC-box elements of the LcTPS42 and LcGPPS.SSU1 promoters. However, the overexpression of LcERF134 in tomatoes had no impact on the synthesis of monoterpenes, thus indicating that LcERF134 is a species-specific TF. Our research demonstrated that LcERF134 significantly increased the biosynthesis of monoterpenes by inducing the expression of LcTPS42 and LcGPPS.SSU1, thus offering insight into how to enhance the flavor of L. cubeba essential oil.

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.

SbMYB3 transcription factor promotes root-specific flavone biosynthesis in Scutellaria baicalensis

Scutellaria baicalensis Georgi produces abundant root-specific flavones (RSFs), which provide various benefits to human health. We have elucidated the complete biosynthetic pathways of baicalein and wogonin. However, the transcriptional regulation of flavone biosynthesis in S. baicalensis remains unclear. We show that the SbMYB3 transcription factor functions as a transcriptional activator involved in the biosynthesis of RSFs in S. baicalensis. Yeast one-hybrid and transcriptional activation assays showed that SbMYB3 binds to the promoter of flavone synthase II-2 (SbFNSII-2) and enhances its transcription. In S. baicalensis hairy roots, RNAi of SbMYB3 reduced the accumulation of baicalin and wogonoside, and SbMYB3 knockout decreased the biosynthesis of baicalein, baicalin, wogonin, and wogonoside, whereas SbMYB3 overexpression enhanced the contents of baicalein, baicalin, wogonin, and wogonoside. Transcript profiling by qRT-PCR demonstrated that SbMYB3 activates SbFNSII-2 expression directly, thus leading to more abundant accumulation of RSFs. This study provides a potential target for metabolic engineering of RSFs.

RNA-Seq Dissects Incomplete Activation of Phytoalexin Biosynthesis by the Soybean Transcription Factors GmMYB29A2 and GmNAC42-1

Glyceollins, isoflavonoid-derived antimicrobial metabolites, are the major phytoalexins in soybean (Glycine max). They play essential roles in providing resistance to the soil-borne pathogen Phytophthora sojae and have unconventional anticancer and neuroprotective activities that render them desirable for pharmaceutical development. Our previous studies revealed that the transcription factors GmMYB29A2 and GmNAC42-1 have essential roles in activating glyceollin biosynthesis, yet each cannot activate the transcription of all biosynthesis genes in the absence of a pathogen elicitor treatment. Here, we report that co-overexpressing both transcription factors is also insufficient to activate glyceollin biosynthesis. To understand this insufficiency, we compared the transcriptome profiles of hairy roots overexpressing each transcription factor with glyceollin-synthesizing roots treated with wall glucan elicitor (WGE) from P. sojae. GmMYB29A2 upregulated most of the WGE-regulated genes that encode enzymatic steps spanning from primary metabolism to the last step of glyceollin biosynthesis. By contrast, GmNAC42-1 upregulated glyceollin biosynthesis genes only when overexpressed in the presence of WGE treatment. This is consistent with our recent discovery that, in the absence of WGE, GmNAC42-1 is bound by GmJAZ1 proteins that inhibit its transactivation activity. WGE, and not GmMYB29A2 or GmNAC42-1, upregulated the heat shock family gene GmHSF6-1, the homolog of Arabidopsis HSFB2a that directly activated the transcription of several glyceollin biosynthesis genes. Our results provide important insights into what biosynthesis genes will need to be upregulated to activate the entire glyceollin biosynthetic pathway.

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.

Transcriptome-wide identification of WRKY transcription factors and their expression profiles in response to methyl jasmonate in Platycodon grandiflorus

Platycodon grandiflorus, a perennial flowering plant widely distributed in China and South Korea, is an excellent resource for both food and medicine. The main active compounds of P. grandiflorus are triterpenoid saponins. WRKY transcription factors (TFs) are among the largest gene families in plants and play an important role in regulating plant terpenoid accumulation, physiological metabolism, and stress response. Numerous studies have been reported on other medicinal plants; however, little is known about WRKY genes in P. grandiflorus. In this study, 27 PgWRKYs were identified in the P. grandiflorus transcriptome. Phylogenetic analysis showed that PgWRKY genes were clustered into three main groups and five subgroups. Transcriptome analysis showed that the PgWRKY gene expression patterns in different tissues differed between those in Tongcheng City (Southern Anhui) and Taihe County (Northern Anhui). Gene expression analysis based on RNA sequencing and qRT-PCR analysis showed that most PgWRKY genes were expressed after induction with methyl jasmonate (MeJA). Co-expressing PgWRKY genes with triterpenoid biosynthesis pathway genes revealed four PgWRKY genes that may have functions in triterpenoid biosynthesis. Additionally, functional annotation and protein-protein interaction analysis of PgWRKY proteins were performed to predict their roles in potential regulatory networks. Thus, we systematically analyzed the structure, evolution, and expression patterns of PgWRKY genes to provide an important theoretical basis for further exploring the molecular basis and regulatory mechanism of WRKY TFs in triterpenoid biosynthesis.

Plant defense under Arctic light conditions: Can plants withstand invading pests?

Global warming is predicted to change the growth conditions for plants and crops in regions at high latitudes (>60° N), including the Arctic. This will be accompanied by alterations in the composition of natural plant and pest communities, as herbivorous arthropods will invade these regions as well. Interactions between previously non-overlapping species may occur and cause new challenges to herbivore attack. However, plants growing at high latitudes experience less herbivory compared to plants grown at lower latitudes. We hypothesize that this finding is due to a gradient of constitutive chemical defense towards the Northern regions. We further hypothesize that higher level of defensive compounds is mediated by higher level of the defense-related phytohormone jasmonate. Because its biosynthesis is light dependent, Arctic summer day light conditions can promote jasmonate accumulation and, hence, downstream physiological responses. A pilot study with bilberry (Vaccinium myrtillus) plants grown under different light regimes supports the hypothesis.

TcJAV3-TcWRKY26 Cascade Is a Missing Link in the Jasmonate-Activated Expression of Taxol Biosynthesis Gene DBAT in Taxus chinensis

Jasmonates (JAs) are the most effective inducers for the biosynthesis of various secondary metabolites. Currently, jasmonate ZIM domain (JAZ) and its interactors, such as MYC2, constitute the main JA signal transduction cascade, and such a cascade fails to directly regulate all the taxol biosynthesis genes, especially the rate-limit gene, DBAT. Another JA signaling branch, JAV and WRKY, would probably fill the gap. Here, TcJAV3 was the closest VQ-motif-containing protein in Taxus chinensis to AtJAV1. Although TcJAV3 was overexpressed in AtJAV1 knockdown mutant, JAVRi17, the enhanced disease resistance to Botrytis cinerea caused by silencing AtJAV1 was completely recovered. The results indicated that TcJAV3 indeed transduced JA signal as AtJAV1. Subsequently, TcWRKY26 was screened out to physically interact with TcJAV3 by using a yeast two-hybrid system. Furthermore, bimolecular fluorescence complementation and luciferase complementary imaging also confirmed that TcJAV3 and TcWRKY26 could form a protein complex in vivo. Our previous reports showed that transient TcWRKY26 overexpression could remarkably increase DBAT expression. Yeast one-hybrid and luciferase activity assays revealed that TcWRKY26 could directly bind with the wa-box of the DBAT promoter to activate downstream reporter genes. All of these results indicated that TcWRKY26 acts as a direct regulator of DBAT, and the TcJAV3−TcWRKY26 complex is actually another JA signal transduction mode that effectively regulates taxol biosynthesis in Taxus. Our results revealed that JAV−WRKY complexes directly regulated DBAT gene in response to JA stimuli, providing a novel model for JA-regulated secondary metabolism. Moreover, JAV could also transduce JA signal and function non-redundantly with JAZ during the regulation of secondary metabolisms.

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.

Cloning, characterization and functional analysis of NtMYB306a gene reveals its role in wax alkane biosynthesis of tobacco trichomes and stress tolerance

Trichomes are specialized hair-like organs found on epidermal cells of many terrestrial plants, which protect plant from excessive transpiration and numerous abiotic and biotic stresses. However, the genetic basis and underlying mechanisms are largely unknown in Nicotiana tabacum (common tobacco), an established model system for genetic engineering and plant breeding. In present study, we identified, cloned and characterized an unknown function transcription factor NtMYB306a from tobacco cultivar K326 trichomes. Results obtained from sequence phylogenetic tree analysis showed that NtMYB306a-encoded protein belonged to S1 subgroup of the plants' R2R3-MYB transcription factors (TFs). Observation of the green fluorescent signals from NtMYB306a-GFP fusion protein construct exhibited that NtMYB306a was localized in nucleus. In yeast transactivation assays, the transformed yeast containing pGBKT7-NtMYB306a construct was able to grow on SD/-Trp-Ade+X-α-gal selection media, signifying that NtMYB306a exhibits transcriptional activation activity. Results from qRT-PCR, in-situ hybridization and GUS staining of transgenic tobacco plants revealed that NtMYB306a is primarily expressed in tobacco trichomes, especially tall glandular trichomes (TGTs) and short glandular trichomes (SGTs). RNA sequencing (RNA-seq) and qRT-PCR analysis of the NtMYB306a-overexpressing transgenic tobacco line revealed that NtMYB306a activated the expression of a set of key target genes which were associated with wax alkane biosynthesis. Gas Chromatography-Mass Spectrometry (GC-MS) exhibited that the total alkane contents and the contents of n-C28, n-C29, n-C31, and ai-C31 alkanes in leaf exudates of NtMYB306a-OE lines (OE-3, OE-13, and OE-20) were significantly greater when compared to WT. Besides, the promoter region of NtMYB306a contained numerous stress-responsive cis-acting elements, and their differential expression towards salicylic acid and cold stress treatments reflected their roles in signal transduction and cold-stress tolerance. Together, these results suggest that NtMYB306a is necessarily a positive regulator of alkane metabolism in tobacco trichomes that does not affect the number and morphology of tobacco trichomes, and that it can be used as a candidate gene for improving stress resistance and the quality of tobacco.