The AP2/ERF transcription factor SmERF1L1 regulates the biosynthesis of tanshinones and phenolic acids in Salvia miltiorrhiza

Physiological and molecular mechanisms of carbon quantum dots alleviating Cu2+ toxicity in Salvia miltiorrhiza bunge

Excessive Cu2+ is toxic to plants. Carbon quantum dots (CQDs) exhibit certain chelating properties towards heavy metals, and they also demonstrate antioxidant activities. To explore the mechanism for alleviating the Cu2+ toxicity of Salvia miltiorrhiza Bunge mediated by CQDs, CQDs that contained CC, CO, H-O, C-N and C-O functional groups with particle size less than 10 nm and that emitted blue fluorescence were prepared. S. miltiorrhiza seedlings were treated with 200 μM of Cu2+ and 500 mg/L of CQDs to relieve stress. Exogenous CQDs effectively restored plant phenotype; reduced Cu2+, H2O2 and malondialdehyde contents and restored total superoxide dismutase, peroxidase and catalase activities under Cu2+ toxicity. Simultaneously, an association network of Cu2+ transport-related and metabolic pathway genes of phenolic acids and terpenoids was established on the basis of cross-species transcriptome analysis. Combined with reverse transcription quantitative real-time polymerase chain reaction analysis, the potential molecular mechanism of CQDs, i.e. promoting phenolic acid biosynthesis to alleviate Cu2+ toxicity, was revealed by activating the expression of key enzyme genes of phenolic acid synthesis. This study provides a theoretical basis for Cu2+ pollution prevention and control in plants. It also laid a foundation for alleviating Cu stress by using CQDs in agricultural production.

The methyl jasmonate-responsive transcription factor SmERF106 promotes tanshinone accumulation in Salvia miltiorrhiza

Understanding the regulatory biosynthesis mechanisms of active compounds in herbs is vital for the preservation and sustainable use of natural medicine resources. Diterpenoids, which play a key role in plant growth and resistance, also serve as practical products for humans. Tanshinone, a class of abietane-type diterpenes unique to the Salvia genus, such as Salvia miltiorrhiza, is an excellent model for studying diterpenoids. In this study, we discovered that a transcription factor, SmERF106, responds to MeJA induction and is located in the nucleus. It exhibits a positive correlation with the expression of SmKSL1 and SmIDI1, which are associated with tanshinone biosynthesis. We performed DNA affinity purification sequencing (DAP-seq) to predict genes that may be transcriptionally regulated by SmERF106. Our cis-elements analysis suggested that SmERF106 might bind to GCC-boxes in the promoters of SmKSL1 and SmIDI1. This indicates that SmKSL1 and SmIDI1 could be potential target genes regulated by SmERF106 in the tanshinone biosynthesis pathway. Their interaction was then demonstrated through a series of in vitro and in vivo binding experiments, including Y1H, EMSA, and Dual-LUC. Overexpression of SmERF106 in the hairy root of S. miltiorrhiza led to a significant increase in tanshinone content and the transcriptional levels of SmKSL1 and SmIDI1. In summary, we found that SmERF106 can activate the transcription of SmKSL1 and SmIDI1 in response to MeJA induction, thereby promoting tanshinone biosynthesis. This discovery provides new insights into the regulatory mechanisms of tanshinones in response to JA and offers a potential gene tool for tanshinone metabolic engineering strategy.

Biosynthesis and signal transduction of plant growth regulators and their effects on bioactive compound production in Salvia miltiorrhiza (Danshen)

Plant growth regulators (PGRs) are involved in multiple aspects of plant life, including plant growth, development, and response to environmental stimuli. They are also vital for the formation of secondary metabolites in various plants. Salvia miltiorrhiza is a famous herbal medicine and has been used commonly for > 2000 years in China, as well as widely used in many other countries. S. miltiorrhiza is extensively used to treat cardiovascular and cerebrovascular diseases in clinical practices and has specific merit against various diseases. Owing to its outstanding medicinal and commercial potential, S. miltiorrhiza has been extensively investigated as an ideal model system for medicinal plant biology. Tanshinones and phenolic acids are primary pharmacological constituents of S. miltiorrhiza. As the growing market for S. miltiorrhiza, the enhancement of its bioactive compounds has become a research hotspot. S. miltiorrhiza exhibits a significant response to various PGRs in the production of phenolic acids and tanshinones. Here, we briefly review the biosynthesis and signal transduction of PGRs in plants. The effects and mechanisms of PGRs on bioactive compound production in S. miltiorrhiza are systematically summarized and future research is discussed. This article provides a scientific basis for further research, cultivation, and metabolic engineering in S. miltiorrhiza.

Physiological and molecular mechanisms of ZnO quantum dots mitigating cadmium stress in Salvia miltiorrhiza

This study delved into the physiological and molecular mechanisms underlying the mitigation of cadmium (Cd) stress in the model medicinal plant Salvia miltiorrhiza through the application of ZnO quantum dots (ZnO QDs, 3.84 nm). A pot experiment was conducted, wherein S. miltiorrhiza was subjected to Cd stress for six weeks with foliar application of 100 mg/L ZnO QDs. Physiological analyses demonstrated that compared to Cd stress alone, ZnO QDs improved biomass, reduced Cd accumulation, increased the content of photosynthetic pigments (chlorophyll and carotenoids), and enhanced the levels of essential nutrient elements (Ca, Mn, and Cu) under Cd stress. Furthermore, ZnO QDs significantly lowered Cd-induced reactive oxygen species (ROS) content, including H2O2, O2-, and MDA, while enhancing the activity of antioxidant enzymes (SOD, POD, APX, and GSH-PX). Additionally, ZnO QDs promoted the biosynthesis of primary and secondary metabolites, such as total protein, soluble sugars, terpenoids, and phenols, thereby mitigating Cd stress in S. miltiorrhiza. At the molecular level, ZnO QDs were found to activate the expression of stress signal transduction-related genes, subsequently regulating the expression of downstream target genes associated with metal transport, cell wall synthesis, and secondary metabolite synthesis via transcription factors. This activation mechanism contributed to enhancing Cd tolerance in S. miltiorrhiza. In summary, these findings shed light on the mechanisms underlying the mitigation of Cd stress by ZnO QDs, offering a potential nanomaterial-based strategy for enhancing Cd tolerance in medicinal plants.

Integrated transcriptomic and CGAs analysis revealed IbGLK1 is a key transcription factor for chlorogenic acid accumulation in sweetpotato (Ipomoea batatas [L.] Lam.) blades

Sweetpotato blades are rich in the functional secondary metabolite chlorogenic acid (CGA), which deepen potential for effective utilization of the blade in industry. In this study, we evaluated the type and content of CGA in the blades of 16 sweetpotato genotypes and analyzed the correlation between CGA content and antioxidant capacity. Then we isolated and characterized IbGLK1, a GARP-type transcription factor, by comparative transcriptome analysis. A subcellular localization assay indicated that IbGLK1 is located in the nucleus. Overexpression and silencing of IbGLK1 in sweetpotato blade resulted in a 0.90-fold increase and 1.84-fold decrease, respectively, in CGA content compared to the control. Yeast one-hybrid and dual-luciferase assays showed that IbGLK1 binds and activates the promoters of IbHCT, IbHQT, IbC4H, and IbUGCT, resulting in the promotion of CGA biosynthesis. In conclusion, our study provides insights into a high-quality gene for the regulation of CGA metabolism and germplasm resources for breeding sweetpotato.

Overexpression of AtMYB2 Promotes Tolerance to Salt Stress and Accumulations of Tanshinones and Phenolic Acid in Salvia miltiorrhiza

Salvia miltiorrhiza is a prized traditional Chinese medicinal plant species. Its red storage roots are primarily used for the treatment of cardiovascular and cerebrovascular diseases. In this study, a transcription factor gene AtMYB2 was cloned and introduced into Salvia miltiorrhiza for ectopic expression. Overexpression of AtMYB2 enhanced salt stress resistance in S. miltiorrhiza, leading to a more resilient phenotype in transgenic plants exposed to high-salinity conditions. Physiological experiments have revealed that overexpression of AtMYB2 can decrease the accumulation of reactive oxygen species (ROS) during salt stress, boost the activity of antioxidant enzymes, and mitigate oxidative damage to cell membranes. In addition, overexpression of AtMYB2 promotes the synthesis of tanshinones and phenolic acids by upregulating the expression of biosynthetic pathway genes, resulting in increased levels of these secondary metabolites. In summary, our findings demonstrate that AtMYB2 not only enhances plant tolerance to salt stress, but also increases the accumulation of secondary metabolites in S. miltiorrhiza. Our study lays a solid foundation for uncovering the molecular mechanisms governed by AtMYB2 and holds significant implications for the molecular breeding of high-quality S. miltiorrhiza varieties.

SmEIL1 transcription factor inhibits tanshinone accumulation in response to ethylene signaling in Salvia miltiorrhiza

Among the bioactive compounds, lipid-soluble tanshinone is present in Salvia miltiorrhiza, a medicinal plant species. While it is known that ethephon has the ability to inhibit the tanshinones biosynthesis in the S. miltiorrhiza hairy root, however the underlying regulatory mechanism remains obscure. In this study, using the transcriptome dataset of the S. miltiorrhiza hairy root induced by ethephon, an ethylene-responsive transcriptional factor EIN3-like 1 (SmEIL1) was identified. The SmEIL1 protein was found to be localized in the nuclei, and confirmed by the transient transformation observed in tobacco leaves. The overexpression of SmEIL1 was able to inhibit the tanshinones accumulation to a large degree, as well as down-regulate tanshinones biosynthetic genes including SmGGPPS1, SmHMGR1, SmHMGS1, SmCPS1, SmKSL1 and SmCYP76AH1. These are well recognized participants in the tanshinones biosynthesis pathway. Further investigation on the SmEIL1 was observed to inhibit the transcription of the CPS1 gene by the Dual-Luciferase (Dual-LUC) and yeast one-hybrid (Y1H) assays. The data in this work will be of value regarding the involvement of EILs in regulating the biosynthesis of tanshinones and lay the foundation for the metabolic engineering of bioactive ingredients in S. miltiorrhiza.

CaERF1- mediated ABA signal positively regulates camptothecin biosynthesis by activating the iridoid pathway in Camptotheca acuminata

Camptotheca acuminata is one of the primary sources of camptothecin (CPT), which is widely used in the treatment of human malignancies because of its inhibitory activity against DNA topoisomerase I. Although several transcription factors have been identified for regulating CPT biosynthesis in other species, such as Ophiorrhiza pumila, the specific regulatory components controlling CPT biosynthesis in C. acuminata have yet to be definitively determined. In this study, CaERF1, an DREB subfamily of the APETALA2/ethylene response factors (AP2ERFs), was identified in C. acuminata. The transient overexpression and silencing of CaERF1 in C. acuminata leaves confirmed that it positively regulates the accumulation of CPT by inducing the expression of CaCYC1 and CaG8O in the iridoid pathway. Results of transient transcriptional activity assay and yeast one-hybrid assays have showed that CaERF1 transcriptionally activates the expression of CaCYC1 and CaG8O by binding to RAA and CEI elements in the promoter regions of these two genes. Furthermore, the expression of CaCYC1 and CaG8O in CaERF1-silenced leaves was less sensitive to ABA treatment, indicating that CaERF1 is a crucial component involved in ABA-regulated CPT biosynthesis in C. acuminata.

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.

APETALA2/ethylene-responsive factors in higher plant and their roles in regulation of plant stress response

Plants, anchored throughout their life cycles, face a unique set of challenges from fluctuating environments and pathogenic assaults. Central to their adaptative mechanisms are transcription factors (TFs), particularly the AP2/ERF superfamily-one of the most extensive TF families unique to plants. This family plays instrumental roles in orchestrating diverse biological processes ranging from growth and development to secondary metabolism, and notably, responses to both biotic and abiotic stresses. Distinguished by the presence of the signature AP2 domain or its responsiveness to ethylene signals, the AP2/ERF superfamily has become a nexus of research focus, with increasing literature elucidating its multifaceted roles. This review provides a synoptic overview of the latest research advancements on the AP2/ERF family, spanning its taxonomy, structural nuances, prevalence in higher plants, transcriptional and post-transcriptional dynamics, and the intricate interplay in DNA-binding and target gene regulation. Special attention is accorded to the ethylene response factor B3 subgroup protein Pti5 and its role in stress response, with speculative insights into its functionalities and interaction matrix in tomatoes. The overarching goal is to pave the way for harnessing these TFs in the realms of plant genetic enhancement and novel germplasm development.

DoAP2/ERF89 activated the terpene synthase gene DoPAES in Dendrobium officinale and participated in the synthesis of β-patchoulene

Dendrobium officinale Kimura et Migo is a tonic plant that has both ornamental and medicinal properties. Terpenoids are significant and diverse secondary metabolites in plants, and are one of the important natural active ingredients in D. officinale. The AP2/ERF gene family plays a major role in primary and secondary metabolism. However, the AP2/ERF transcription factor family has not been identified in D. officinale, and it is unclear if it is involved in the regulation of terpenoid biosynthesis. This study identified a sesquiterpene synthetase-β-patchoulene synthase (DoPAES) using transcriptome and terpenic metabolic profile analyses. A total of 111 members of the AP2/ERF family were identified through the whole genome of D. officinale. The tissue-specific expression and gene co-expression pattern of the DoAP2/ERF family members were analyzed. The results showed that the expression of DoPAES was highly correlated with the expression of DoAP2/ERF89 and DoAP2/ERF47. The yeast one-hybrid (Y1H) assays and dual-luciferase experiments demonstrated that DoAP2/ERF89 and DoAP2/ERF47 could regulate the expression of DoPAES. The transcriptional regulatory effects were examined using homologous transient expression of DoAP2/ERF89 in protocorms of D. officinale. DoAP2/ERF89 positively regulated the biosynthesis of β-patchoulene. This study showed that DoAP2/ERF89 can bind to the promoter region of DoPAES to control its expression and further regulate the biosynthesis of β-patchoulene in D. officinale. These results provide new insights on the regulation of terpenoid biosynthesis.

Adipose tissue inflammation linked to obesity: A review of current understanding, therapies and relevance of phyto-therapeutics

Obesity is a current global challenge affecting all ages and is characterized by the up-regulated secretion of bioactive factors/pathways which result in adipose tissue inflammation (ATI). Current obesity therapies are mainly focused on lifestyle (diet/nutrition) changes. This is because many chemosynthetic anti-obesogenic medications cause adverse effects like diarrhoea, dyspepsia, and faecal incontinence, among others. As such, it is necessary to appraise the efficacies and mechanisms of action of safer, natural alternatives like plant-sourced compounds, extracts [extractable phenol (EP) and macromolecular antioxidant (MA) extracts], and anti-inflammatory peptides, among others, with a view to providing a unique approach to obesity care. These natural alternatives may constitute potent therapies for ATI linked to obesity. The potential of MA compounds (analysed for the first time in this review) and extracts in ATI and obesity management is elucidated upon, while also highlighting research gaps and future prospects. Furthermore, immune cells, signalling pathways, genes, and adipocyte cytokines play key roles in ATI responses and are targeted in certain therapies. As a result, this review gives an in-depth appraisal of ATI linked to obesity, its causes, mechanisms, and effects of past, present, and future therapies for reversal and alleviation of ATI. Achieving a significant decrease in morbidity and mortality rates attributed to ATI linked to obesity and related comorbidities is possible as research improves our understanding over time.

The SmERF1b-like regulates tanshinone biosynthesis in Salvia miltiorrhiza hairy root

The ethylene response factor family genes are involved in the regulation of secondary metabolism in Salvia miltiorrhiza, but the mechanism underlying this regulation remains elusive. In the present study, based on the cDNA library of S. miltiorrhiza, an AP2/ERF gene was cloned and named SmERF1b-like. This gene exhibited a significant response to exogenous ethylene supply, such that ethylene remarkably upregulated SmERF1b-like expression levels in the leaves of S. miltiorrhiza. Subcellular localization showed that SmERF1b-like is located in the nucleus. Furthermore, SmERF1b-like showed a binding affinity with a GCC-box motif in the promoter region of genes associated with tanshinone biosynthesis in S. miltiorrhiza. Overexpression of SmERF1b-like in hairy roots of S. miltiorrhiza substantially upregulated SmCPS1 and SmKSL1 expression levels, resulting in increased biosynthesis of tanshinone I and cryptotanshinone contents. This finding provides valuable theoretical support for the utilization of a plant genetic engineering strategy to enhance S. miltiorrhiza resources.

Identification and characterization of a novel tyrosine aminotransferase gene (SmTAT3-2) promotes the biosynthesis of phenolic acids in Salvia miltiorrhiza Bunge

Rosmarinic acid (RA) and salvianolic acid B (SAB) are main phenolic acids in Salvia miltiorrhiza Bunge have been widely used in the treatment of cardiovascular and cerebrovascular diseases due to their excellent pharmacological activity. RA is a precursor of SAB, and tyrosine transaminase (TAT, EC 2.6.1.5) is a crucial rate-limiting enzyme in their metabolism pathway. This study identified a novel TAT gene, SmTAT3-2, and found that it is a new transcript derived from unconventional splicing of SmTAT3. We used different substrates for enzymatic reaction with SmTAT1, SmTAT3 and SmTAT3-2. Subcellular localization of SmTAT1 and SmTAT3-2 was completed based on submicroscopic techniques. In addition, they were overexpressed and CRISPR/Cas9 gene edited in hairy roots of S. miltiorrhiza. Revealed SmTAT3-2 and SmTAT1 showed a stronger affinity for L-tyrosine than SmTAT3, localized in the cytoplasm, and promoted the synthesis of phenolic acid. In overexpressed SmTAT3-2 hairy roots, the content of RA and SAB was significantly increased by 2.53 and 3.38 fold, respectively, which was significantly higher than that of overexpressed SmTAT1 strain compared with EV strain. These findings provide a valuable key enzyme gene for the phenolic acids metabolism pathway and offer a theoretical basis for the clinical application.

Functions of Representative Terpenoids and Their Biosynthesis Mechanisms in Medicinal Plants

Terpenoids are the broadest and richest group of chemicals obtained from plants. These plant-derived terpenoids have been extensively utilized in various industries, including food and pharmaceuticals. Several specific terpenoids have been identified and isolated from medicinal plants, emphasizing the diversity of biosynthesis and specific functionality of terpenoids. With advances in the technology of sequencing, the genomes of certain important medicinal plants have been assembled. This has improved our knowledge of the biosynthesis and regulatory molecular functions of terpenoids with medicinal functions. In this review, we introduce several notable medicinal plants that produce distinct terpenoids (e.g., Cannabis sativa, Artemisia annua, Salvia miltiorrhiza, Ginkgo biloba, and Taxus media). We summarize the specialized roles of these terpenoids in plant-environment interactions as well as their significance in the pharmaceutical and food industries. Additionally, we highlight recent findings in the fields of molecular regulation mechanisms involved in these distinct terpenoids biosynthesis, and propose future opportunities in terpenoid research, including biology seeding, and genetic engineering in medicinal plants.

Contemporary understanding of transcription factor regulation of terpenoid biosynthesis in plants

KEY MESSAGE

This review summarized how TFs function independently or in response to environmental factors to regulate terpenoid biosynthesis via fine-tuning the expression of rate-limiting enzymes. Terpenoids are derived from various species and sources. They are essential for interacting with the environment and defense mechanisms, such as antimicrobial, antifungal, antiviral, and antiparasitic properties. Almost all terpenoids have high medicinal value and economic performance. Recently, the control of enzyme genes on terpenoid biosynthesis has received a great deal of attention, but transcriptional factors regulatory network on terpenoid biosynthesis and accumulation has yet to get a thorough review. Transcription factors function as activators or suppressors independently or in response to environmental stimuli, fine-tuning terpenoid accumulation through regulating rate-limiting enzyme expression. This study investigates the advancements in transcription factors related to terpenoid biosynthesis and systematically summarizes previous works on the specific mechanisms of transcription factors that regulate terpenoid biosynthesis via hormone signal-transcription regulatory networks in plants. This will help us to better comprehend the regulatory network of terpenoid biosynthesis and build the groundwork for terpenoid development and effective utilization.

Role of bZIP transcription factors in the regulation of plant secondary metabolism

MAIN CONCLUSION

This study provides an overview of the structure, classification, regulatory mechanisms, and biological functions of the basic (region) leucine zipper transcription factors and their molecular mechanisms in flavonoid, terpenoid, alkaloid, phenolic acid, and lignin biosynthesis. Basic (region) leucine zippers (bZIPs) are evolutionarily conserved transcription factors (TFs) in eukaryotic organisms. The bZIP TFs are widely distributed in plants and play important roles in plant growth and development, photomorphogenesis, signal transduction, resistance to pathogenic microbes, biotic and abiotic stress, and secondary metabolism. Moreover, the expression of bZIP TFs not only promotes or inhibits the accumulation of secondary metabolites in medicinal plants, but also affects the stress response of plants to the external adverse environment. This paper describes the structure, classification, biological function, and regulatory mechanisms of bZIP TFs. In addition, the molecular mechanism of bZIP TFs regulating the biosynthesis of flavonoids, terpenoids, alkaloids, phenolic acids, and lignin are also elaborated. This review provides a summary for in-depth study of the molecular mechanism of bZIP TFs regulating the synthesis pathway of secondary metabolites and plant molecular breeding, which is of significance for the generation of beneficial secondary metabolites and the improvement of plant varieties.

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.

Jasmonic acid regulates the biosynthesis of medicinal metabolites via the JAZ9-MYB76 complex in Salvia miltiorrhiza

Jasmonic acid (JA) signaling pathway plays an important role in tanshinone and phenolic acid biosynthesis in Salvia miltiorrhiza. However, the specific regulatory mechanism remains largely unclear. Previous work showed that a JASMONATE ZIM-domain (JAZ) protein, SmJAZ9, acted as a repressor of tanshinone production in S. miltiorrhiza. In this study, we revealed that SmJAZ9 reduced both phenolic acid accumulation and related biosynthetic gene expression, confirming that SmJAZ9 also negatively affected phenolic acid biosynthesis. Then, we identified a novel MYB transcription factor, SmMYB76, which interacted with SmJAZ9. SmMYB76 repressed phenolic acid biosynthesis by directly downregulating SmPAL1, Sm4CL2, and SmRAS1. Further investigation demonstrated that JA mediated phenolic acids biosynthesis via SmJAZ9-SmMYB76 complex. Taken together, these findings state the molecular mechanism that SmJAZ9-SmMYB76 regulated phenolic acid biosynthesis at the transcriptional and protein levels, which provided new insights into JA signaling pathway regulating plant metabolism.

Isolation of Salvia miltiorrhiza Kaurene Synthase-like (KSL) Gene Promoter and Its Regulation by Ethephon and Yeast Extract

The presented study describes the regulation of the promoter region of the Salvia miltiorrhiza kaurene synthase-like gene (SmKSL) by ethylene and yeast extract. The isolated fragment is 897 bp and is composed of a promoter (763 bp), 5'UTR (109 bp), and a short CDS (25 bp). The initial in silico analysis revealed the presence of numerous putative cis-active sites for trans-factors responding to different stress conditions. However, this study examines the influence of ethylene and yeast extract on SmKSL gene expression and tanshinone biosynthesis regulation. The results of 72h RT-PCR indicate an antagonistic interaction between ethylene, provided as ethephon (0.05, 0.10, 0.25, and 0.50 mM), and yeast extract (0.5%) on SmKSL gene expression in callus cultures of S. miltiorrhiza. A similar antagonistic effect was observed on total tanshinone concentration for up to 60 days. Ethylene provided as ethephon (0.05, 0.10, 0.25, and 0.50 mM) is a weak inducer of total tanshinone biosynthesis, increasing them only up to the maximum value of 0.67 ± 0.04 mg g^-1 DW (60-day induction with 0.50 mM ethephon). Among the tanshinones elicited by ethephon, cryptotanshinone (52.21%) dominates, followed by dihydrotanshinone (45.00%) and tanshinone IIA (3.79%). In contrast, the 0.5% yeast extract strongly increases the total tanshinone concentration up to a maximum value of 13.30 ± 1.09 mg g^-1 DW, observed after 50 days of induction. Yeast extract and ethylene appear to activate different fragments of the tanshinone biosynthesis route; hence the primary tanshinones induced by yeast extract were cryptotanshinone (81.42%), followed by dihydrotanshinone (17.06%) and tanshinone IIA (1.52%).

Transcriptome analysis reveals that jasmonic acid biosynthesis and signaling is associated with the biosynthesis of asperosaponin VI in Dipsacus asperoides

Dipsacus asperoides is a perennial herb, the roots of which are abundant in asperosaponin VI, which has important medicinal value. However, the molecular mechanism underlying the biosynthesis of asperosaponin VI in D. asperoides remains unclear. In present study, a comprehensive investigation of asperosaponin VI biosynthesis was conducted at the levels of metabolite and transcript during root development. The content of asperosaponin VI was significantly accumulated in two-leaf stage roots, and the spatial distribution of asperosaponin VI was localized in the xylem. The concentration of asperosaponin VI gradually increased in the root with the development process. Transcriptome analysis revealed 3916 unique differentially expressed genes (DEGs) including 146 transcription factors (TFs) during root development in D. asperoides. In addition, α-linolenic acid metabolism, jasmonic acid (JA) biosynthesis, JA signal transduction, sesquiterpenoid and triterpenoid biosynthesis, and terpenoid backbone biosynthesis were prominently enriched. Furthermore, the concentration of JA gradually increased, and genes involved in α-linolenic acid metabolism, JA biosynthesis, and triterpenoid biosynthesis were up-regulated during root development. Moreover, the concentration of asperosaponin VI was increased following methyl jasmonate (MeJA) treatment by activating the expression of genes in the triterpenoid biosynthesis pathway, including acetyl-CoA acetyltransferase (DaAACT), 3-hydroxy-3-methylglutaryl coenzyme A synthase (DaHMGCS), 3-hydroxy-3-methylglutaryl coenzyme-A reductase (DaHMGCR). We speculate that JA biosynthesis and signaling regulates the expression of triterpenoid biosynthetic genes and facilitate the biosynthesis of asperosaponin VI. The results suggest a regulatory network wherein triterpenoids, JA, and TFs co-modulate the biosynthesis of asperosaponin VI in D. asperoides.

Transcription Factor SmSPL2 Inhibits the Accumulation of Salvianolic Acid B and Influences Root Architecture

The SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL) transcription factor play vital roles in plant growth and development. Although 15 SPL family genes have been recognized in the model medical plant Salvia miltiorrhiza Bunge, most of them have not been functionally characterized to date. Here, we performed a careful characterization of SmSPL2, which was expressed in almost all tissues of S. miltiorrhiza and had the highest transcriptional level in the calyx. Meanwhile, SmSPL2 has strong transcriptional activation activity and resides in the nucleus. We obtained overexpression lines of SmSPL2 and rSmSPL2 (miR156-resistant SmSPL2). Morphological changes in roots, including longer length, fewer adventitious roots, decreased lateral root density, and increased fresh weight, were observed in all of these transgenic lines. Two rSmSPL2-overexpressed lines were subjected to transcriptome analysis. Overexpression of rSmSPL2 changed root architectures by inhibiting biosynthesis and signal transduction of auxin, while triggering that of cytokinin. The salvianolic acid B (SalB) concentration was significantly decreased in rSmSPL2-overexpressed lines. Further analysis revealed that SmSPL2 binds directly to the promoters of Sm4CL9, SmTAT1, and SmPAL1 and inhibits their expression. In conclusion, SmSPL2 is a potential gene that efficiently manipulate both root architecture and SalB concentration in S. miltiorrhiza.

The SmMYB36-SmERF6/SmERF115 module regulates the biosynthesis of tanshinones and phenolic acids in salvia miltiorrhiza hairy roots

Tanshinone and phenolic acids are the most important active substances of Salvia miltiorrhiza, and the insight into their transcriptional regulatory mechanisms is an essential process to increase their content in vivo. SmMYB36 has been found to have important regulatory functions in the synthesis of tanshinone and phenolic acid; paradoxically, its mechanism of action in S. miltiorrhiza is not clear. Here, we demonstrated that SmMYB36 functions as a promoter of tanshinones accumulation and a suppressor of phenolic acids through the generation of SmMYB36 overexpressed and chimeric SmMYB36-SRDX (EAR repressive domain) repressor hairy roots in combination with transcriptomic-metabolomic analysis. SmMYB36 directly down-regulate the key enzyme gene of primary metabolism, SmGAPC, up-regulate the tanshinones biosynthesis branch genes SmDXS2, SmGGPPS1, SmCPS1 and down-regulate the phenolic acids biosynthesis branch enzyme gene, SmRAS. Meanwhile, SmERF6, a positive regulator of tanshinone synthesis activating SmCPS1, was up-regulated and SmERF115, a positive regulator of phenolic acid biosynthesis activating SmRAS, was down-regulated. Furthermore, the seven acidic amino acids at the C-terminus of SmMYB36 are required for both self-activating domain and activation of target gene expression. As a consequence, this study contributes to reveal the potential relevance of transcription factors synergistically regulating the biosynthesis of tanshinone and phenolic acid.

Mining of the CULLIN E3 ubiquitin ligase genes in the whole genome of Salvia miltiorrhiza

CULLIN (CUL) proteins are E3 ubiquitin ligases that are involved in a wide variety of biological processes as well as in response to stress in plants. In Salvia miltiorrhiza, CUL genes have not been characterized and its role in plant development, stress response and secondary metabolite synthesis have not been studied. In this study, genome-wide analyses were performed to identify and to predict the structure and function of CUL of S. miltiorrhiza. Eight CUL genes were identified from the genome of S. miltiorrhiza. The CUL genes were clustered into four subgroups according to phylogenetic relationships. The CUL domain was highly conserved across the family of CUL genes. Analysis of cis-acting elements suggested that CUL genes might play important roles in a variety of biological processes, including abscission reaction acid (ABA) processing. To investigate this hypothesis, we treated hairy roots of S. miltiorrhiza with ABA. The expression of CUL genes varied obviously after ABA treatment. Co-expression network results indicated that three CUL genes might be involved in the biosynthesis of phenolic acid or tanshinone. In summary, the mining of the CUL genes in the whole genome of S. miltiorrhiza contribute novel information to the understanding of the CUL genes and its functional roles in plant secondary metabolites, growth and development.

Genome-wide transcriptome analysis reveals the regulatory network governing terpene trilactones biosynthesis in Ginkgo biloba

Ginkgo biloba L. is currently the only remaining gymnosperm of the Ginkgoaceae Ginkgo genus, and its history can be traced back to the Carboniferous 200 million years ago. Terpene trilactones (TTLs) are one of the main active ingredients in G. biloba, including ginkgolides and bilobalide. They have a good curative effect on cardiovascular and cerebrovascular diseases because of their special antagonistic effect on platelet-activating factors. Therefore, it is necessary to deeply mine genes related to TTLs and to analyze their transcriptional regulation mechanism, which will hold vitally important scientific and practical significance for quality improvement and regulation of G. biloba. In this study, we performed RNA-Seq on the root, stem, immature leaf, mature leaf, microstrobilus, ovulate strobilus, immature fruit and mature fruit of G. biloba. The TTL regulatory network of G. biloba in different organs was revealed by different transcriptomic analysis strategies. Weighted gene co-expression network analysis (WGCNA) revealed that the five modules were closely correlated with organs. The 12 transcription factors, 5 structural genes and 24 Cytochrome P450 (CYP450) were identified as candidate regulators for TTL accumulation by WGCNA and cytoscape visualization. Finally, 6 APETALA2/ethylene response factors, 2 CYP450s and bHLH were inferred to regulate the metabolism of TTLs by correlation analysis. This study is the comprehensive in authenticating transcription factors, structural genes and CYP450 involved in TTL biosynthesis, thereby providing molecular evidence for revealing the comprehensive regulatory network involved in TTL metabolism in G. biloba.

AabHLH112, a bHLH transcription factor, positively regulates sesquiterpenes biosynthesis in Artemisia annua

The bHLH transcription factors play important roles in the regulation of plant growth, development, and secondary metabolism. β-Caryophyllene, epi-cedrol, and β-farnesene, three kinds of sesquiterpenes mainly found in plants, are widely used as spice in the food industry and biological pesticides in agricultural production. Furthermore, they also have a significant value in the pharmaceutical industry. However, there is currently a lack of knowledge on the function of bHLH family TFs in β-caryophyllene, epi-cedrol, and β-farnesene biosynthesis. Here, we found that AabHLH112 transcription factor had a novel function to positively regulate β-carophyllene, epi-cedrol, and β-farnesene biosynthesis in Artemisia annua. Exogenous MeJA enhanced the expression of AabHLH112 and genes of β-caryophyllene synthase (CPS), epi-cedrol synthase (ECS), and β-farnesene synthase (BFS), as well as sesquiterpenes content. Dual-LUC assay showed the activation of AaCPS, AaECS, and AaBFS promoters were enhanced by AabHLH112. Yeast one-hybrid assay showed AabHLH112 could bind to the G-box (CANNTG) cis-element in promoters of both AaCPS and AaECS. In addition, overexpression of AabHLH112 in A. annua significantly elevated the expression levels of AaCPS, AaECS, and AaBFS as well as the contents of β-caryophyllene, epi-cedrol, and β-farnesene, while suppressing AabHLH112 expression by RNAi reduced the expression of the three genes and the contents of the three sesquiterpenes. These results suggested that AabHLH112 is a positive regulator of β-caryophyllene, epi-cedrol, and β-farnesene biosynthesis in A. annua.

Functional pleiotropism, diversity, and redundancy of Salvia miltiorrhiza Bunge JAZ family proteins in jasmonate-induced tanshinone and phenolic acid biosynthesis

Jasmonate (JA) signaling regulates plant growth and development, biotic and abiotic stress tolerance, and primary and secondary metabolism biosynthesis. It is extensively modulated by JA-ZIM-domain (JAZ) family genes. In previous work, we obtained nine SmJAZ genes of Salvia miltiorrhiza and proved that SmJAZ8 was the core repressor of JA-induced tanshinone and phenolic acid biosynthesis. Here, we demonstrate that SmJAZ3 and SmJAZ4 act as repressors of JA-induced biosynthesis of tanshinones and salvianolic acid B (Sal B). This suggests that SmJAZ3/4 are functionally redundant in tanshinone and Sal B biosynthesis. SmJAZ1/2/5/6/9 are activators of JA-induced tanshinone biosynthesis and repressors of JA-induced Sal B biosynthesis. This demonstrates the redundancy and diversity of SmJAZ1/2/5/6/9 functions. Besides, SmJAZ10 inhibited JA-induced Sal B synthesis, but had no effect on the synthesis of tanshinone. Two-hybrid screening (Y2H) showed that SmJAZs formed homologous or heterogeneous dimers. Y2H and firefly luciferase complementation imaging (LCI) assays revealed that SmJAZs also formed a complex regulatory network with SmMYC2a, SmMYC2b, SmMYB39, and SmPAP1. Quantitative reverse transcription-PCR (qRT-PCR) indicated that SmJAZs regulated each other at the transcriptional level. Herein, we prove that SmJAZs have functional pleiotropism, diversity, and redundancy in JA-induced tanshinone and phenolic acid biosynthesis. This study provides an important clue for further understanding the inherent biological significance and molecular mechanisms of the JAZ family as the gene number increases during plant evolution.

Transcriptome sequencing and signal transduction for the enhanced tanshinone production in Salvia miltiorrhiza hairy roots induced by Trichoderma atroviride D16 polysaccharide fraction

Salvia miltiorrhiza Bunge. is commonly used to treat vascular diseases because of its activity ingredients, phenolic acids, and tanshinones. Polysaccharide fraction (PSF) extracted from Trichoderma atroviride D16 could promote tanshinone accumulation in S. miltiorrhiza hairy roots. Transcriptome sequencing was conducted to describe the global gene expression of PSF-treatment hairy roots, and data analyses showed enzymes of tanshinone biosynthetic pathways were up-regulated, and genes associated to signal molecules and transcription factors were responsive. Endogenous H2O2, abscisic acid, and nitric oxide contents were measured after PSF treatment, while tanshinone accumulations were measured with treatment of exogenous H2O2 or H2O2 inhibitor on PSF-treatment S. miltiorrhiza hairy roots. The results showed H2O2 was important in tanshinone biosynthesis caused by PSF and nitric oxide might be the downstream molecules of H2O2. Taken together, the study indicates that D16 PSF enhances the accumulation of tanshinones through enzymes of tanshinone biosynthetic pathways, signal molecules, and transcription factors.

MAPKK2/4/5/7-MAPK3-JAZs modulate phenolic acid biosynthesis in Salvia miltiorrhiza

Phenolic acids are the major bioactive metabolites produced in Salvia miltiorrhiza, a traditional Chinese medicine called Danshen. Many phytohormone elicitor treatments induce phenolic acid biosynthesis, even though the underlying mechanism remains obscure. Expression pattern analysis showed that SmMAPK3 was highly expressed in leaves, and SmMAPK3 was significantly induced by salicylic acid (SA) and methyl jasmonate (JA). Bioinformatics analysis revealed that SmMAPK3 belongs to group A and contains a TEY motif in the activation loop together with three conserved regions (P-loop, C-loop and CD-domain). A previous study speculated that SmMAPK3 is likely a positive regulator in the biosynthesis of phenolic acids in S. miltiorrhiza. In this study, overexpression of SmMAPK3 increased phenolic acid biosynthetic gene expression and enhanced the accumulation of phenolic acids in S. miltiorrhiza plantlets. Yeast two-hybrid (Y2H) analysis and firefly luciferase complementation imaging (LCI) assays revealed that SmMAPKK2/4/5/7-SmMAPK3-SmJAZs form a cascade that regulates the accumulation of phenolic acids. In summary, this work deepens our understanding of the posttranscriptional regulatory mechanisms of phenolic acid biosynthesis and sheds new light on metabolic engineering in S. miltiorrhiza.

LcERF19, an AP2/ERF transcription factor from Litsea cubeba, positively regulates geranial and neral biosynthesis

The APETALA2/ETHYLENE RESPONSE FACTOR (AP2/ERF) transcription factors (TFs) are involved in the regulation of specialized terpenoid biosynthesis. However, the AP2/ERF TFs in Litsea cubeba have not been characterized and their role in the biosynthesis of terpenoids is unknown. Here, 174 LcAP2/ERF TFs were identified in L. cubeba and categorized into four subfamilies: 27 AP2, 7 RAV, 1 Soloist, and 139 ERF. Transcriptomic and qRT-PCR assays both showed that the expression levels of LcERF19 were similar to that of terpene synthase LcTPS42 in the pericarp, which is related to the synthesis of geranial and neral in L. cubeba. LcERF19 was further shown to encode a nuclear-localized protein and its expression was strongly induced by jasmonate. Yeast one-hybrid and dual-luciferase assays showed that LcERF19 associated with GCC box elements of the LcTPS42 promoter and promoted its activity. Transient overexpression of LcERF19 in L. cubeba and overexpression of LcERF19 in tomato resulted in a significant increase in geranial and neral. Our findings show that LcERF19 enhances geranial and neral biosynthesis through activation of LcTPS42 expression, which provides a strategy to improve the flavor of tomato and other fruits.

Integrated Transcriptomics and Proteomics to Reveal Regulation Mechanism and Evolution of SmWRKY61 on Tanshinone Biosynthesis in Salvia miltiorrhiza and Salvia castanea

Tanshinones found in Salvia species are the main active compounds for the treatment of cardiovascular and cerebrovascular diseases, but their contents are hugely different in different species. For example, tanshinone IIA content in Salvia castanea Diels f. tomentosa Stib. is about 49 times higher than that in Salvia miltiorrhiza Bunge. The molecular mechanism responsible for this phenomenon remains largely unknown. To address this, we performed comparative transcriptomic and proteomic analyses of S. miltiorrhiza and S. castanea. A total of 296 genes in S. castanea and 125 genes in S. miltiorrhiza were highly expressed at both the transcriptional and proteome levels, including hormone signal regulation, fungus response genes, transcription factors, and CYP450. Among these differentially expressed genes, the expression of SmWRKY61 was particularly high in S. castanea. Overexpression of SmWRKY61 in S. miltiorrhiza could significantly increase the content of tanshinone I and tanshinone IIA, which were 11.09 and 33.37 times of the control, respectively. Moreover, SmWRKY61 had a strong regulatory effect, elevating the expression levels of tanshinone pathway genes such as DXS2, CMK, HMGS2, 1, KSL1, KSL2, CYP76AH1, and CYP76AK3. For the WRKY family, 79 SmWRKYs were originally obtained and classified into three main groups. Collinearity analysis indicated a more specific extension of WRKY gene family in Salvia genus. In 55 Salvia species, only 37 species contained the WRKY61 sequence, and high SmWRKY61 expression in some Salvia L. species was often accompanied by high tanshinone accumulation. The above results suggest that SmWRKY61 is a highly effective regulator of tanshinone accumulation and may be a key factor resulting in high tanshinone accumulation in S. castanea.

SmbHLH60 and SmMYC2 antagonistically regulate phenolic acids and anthocyanins biosynthesis in Salvia miltiorrhiza

INTRODUCTION

Salvia miltiorrhiza is a renowned traditional Chinese medicinal plant with extremely high medicinal value, especially for cardiovascular and cerebrovascular diseases. The jasmonic acid (JA) signaling pathway plays an important role in the improved biosynthesis of secondary metabolites, which is mediated by a major transcriptional regulator, MYC2. However, the JA regulatory mechanism of secondary metabolites biosynthesis in S. miltiorrhiza is still largely unknown.

OBJECTIVES

Our work focuses on the dissection of the molecular mechanism of transcriptional regulation in MeJA-mediated biosynthesis of medicinal components of S. miltiorrhiza. We examined the role of MeJA-responsive bHLH transcription factors (TFs) in improving bioactive secondary metabolites accumulation in S. miltiorrhiza.

METHODS

Hairy root transformation based on CRISPR/Cas9 technique was used to decipher gene function(s). Changes in the content of phenolic acids were evaluated by HPLC. Y1H, EMSA and dual-LUC assays were employed to analyze the molecular mechanism of SmbHLH60 in the regulation on the biosynthesis of phenolic acids and anthocyanins. Y2H, BiFC and pull-down affinity assays were used to corroborate the interaction between SmbHLH60 and SmMYC2.

RESULTS

Being one of the most significantly negatively regulated bHLH genes by MeJA, a new transcription factor SmbHLH60 was discovered and characterized. Over-expression of SmbHLH60 resulted in significant inhibition of phenolic acid and anthocyanin biosynthesis in S. miltiorrhiza by transcriptionally repressing of target genes such as SmTAT1 and SmDFR, whereas CRISPR/Cas9-generated knockout of SmbHLH60 resulted in the opposite effect. In addition, SmbHLH60 and SmMYC2 formed a heterodimer to antagonistically regulate phenolic acid and anthocyanin biosynthesis.

CONCLUSION

Our results clarified that SmbHLH60 is a negativeregulator on the biosynthesis of phenolic acids and anthocyanins. SmbHLH60 competed with SmMYC2 in an antagonistic manner, providing new insights for the molecular mechanism of MeJA-mediated regulation on the biosynthesis of secondary metabolites in S. miltiorrhiza.

Overexpression of SmSCR1 Promotes Tanshinone Accumulation and Hairy Root Growth in Salvia miltiorrhiza

Lipid-soluble tanshinone is one of the main bioactive substances in the medicinal plant Salvia miltiorrhiza, and its medicinal demand is growing rapidly. Yeast extract (YE) modulates the tanshinone biosynthesis, but the underlying regulatory network remains obscure. In this study, a YE-responsive transcriptional factor Scarecrow1 (SCR1) was identified in S. miltiorrhiza from the YE-induced transcriptome dataset. SmSCR1 is located in the nucleus. Overexpression of SmSCR1 in S. miltiorrhiza roots resulted in a significantly higher accumulation of tanshinone than the control, with the highest 1.49-fold increase. We also detected upregulation of tanshinone biosynthetic genes, SmSCR1 and SmHMGR1, and distinct alteration of growth and development of the hairy roots in the overexpression lines compared to the control. An inverse phenotype was observed in SmSCR1-SRDX suppression expression lines. We found that SmSCR1 can bind to the promoter of SmCPS1 to induce its expression. This study provides new insight into the regulatory mechanism on the growth and development of hairy roots, tanshinone accumulation, and the metabolic engineering of bioactive compounds in S. miltiorrhiza.

Comparative transcriptome analyses of different Salvia miltiorrhiza varieties during the accumulation of tanshinones

Salvia miltiorrhiza (Labiatae) is an important medicinal plant in traditional Chinese medicine. Tanshinones are one of the main active components of S. miltiorrhiza. It has been found that the intraspecific variation of S. miltiorrhiza is relatively large and the content of tanshinones in its roots of different varieties is also relatively different. To investigate the molecular mechanisms that responsible for the differences among these varieties, the tanshinones content was determined and comparative transcriptomics analysis was carried out during the tanshinones accumulation stage. A total of 52,216 unigenes were obtained from the transcriptome by RNA sequencing among which 23,369 genes were differentially expressed among different varieties, and 2,016 genes including 18 diterpenoid biosynthesis-related genes were differentially expressed during the tanshinones accumulation stage. Functional categorization of the differentially expressed genes (DEGs) among these varieties revealed that the pathway related to photosynthesis, oxidative phosphorylation, secondary metabolite biosynthesis, diterpenoid biosynthesis, terpenoid backbone biosynthesis, sesquiterpenoid and triterpenoid biosynthesis are the most differentially regulated processes in these varieties. The six tanshinone components in these varieties showed different dynamic changes in tanshinone accumulation stage. In addition, combined with the analysis of the dynamic changes, 277 DEGs (including one dehydrogenase, three CYP450 and 24 transcription factors belonging to 12 transcription factor families) related to the accumulation of tanshinones components were obtained. Furthermore, the KEGG pathway enrichment analysis of these 277 DEGs suggested that there might be an interconnection between the primary metabolic processes, signaling processes and the accumulation of tanshinones components. This study expands the vision of intraspecific variation and gene regulation mechanism of secondary metabolite biosynthesis pathways in medicinal plants from the “omics” perspective.

Integrative Omics Analyses Reveal the Effects of Copper Ions on Salvianolic Acid Biosynthesis

Salvianolic acids, a group of secondary metabolites produced by Salvia miltiorrhiza, are widely used for treating cerebrovascular diseases. Copper is recognized as a necessary microelement and plays an essential role in plant growth. At present, the effect of copper on the biosynthesis of SalAs is unknown. Here, an integrated metabolomic and transcriptomic approach, coupled with biochemical analyses, was employed to dissect the mechanisms by which copper ions induced the biosynthesis of SalAs. In this study, we identified that a low concentration (5 μM) of copper ions could promote growth of S. miltiorrhiza and the biosynthesis of SalAs. Results of the metabolomics analysis showed that 160 metabolites (90 increased and 70 decreased) were significantly changed in S. miltiorrhiza treated with low concentration of copper ions. The differential metabolites were mainly involved in amino acid metabolism, the pentose phosphate pathway, and carbon fixation in photosynthetic organisms. The contents of chlorophyll a, chlorophyll b, and total chlorophyll were significantly increased in leaves of low concentration of copper-treated S. miltiorrhiza plants. Importantly, core SalA biosynthetic genes (laccases and rosmarinic acid synthase), SalA biosynthesis-related transcription factors (MYBs and zinc finger CCCH domain-containing protein 33), and chloroplast proteins-encoding genes (blue copper protein and chlorophyll-binding protein) were upregulated in the treated samples as indicated by a comprehensive transcriptomic analysis. Bioinformatics and enzyme activity analyses showed that laccase 20 contained copper-binding motifs, and its activity in low concentration of copper ions-treated S. miltiorrhiza was much higher than that in the control. Our results demonstrate that enhancement of copper ions of the accumulation of SalAs might be through regulating laccase 20, MYBs, and zinc finger transcription factors, and photosynthetic genes.

Genome-wide characterization and expression analysis of AP2/ERF genes in eggplant (Solanum melongena L.)

The AP2/ERF (APETALA2/Ethylene Response Factor) transcription factor superfamily plays crucial roles in a slew of physiological processes, such as plant growth and development, stress response, and secondary metabolites biosynthesis. Eggplant, especially the one rich with anthocyanins, is an economically important horticultural vegetable cultivated worldwide. In this study, we comprehensively analyzed the putative AP2/ERF gene family members and their response to abiotic stress in eggplant. As per the phylogenetic, conserved domains, and motif analysis, 178 AP2/ERF genes in this study belonged to five subfamilies. Chromosomal distributions analysis elucidated stochastic distribution of 178 putative SmAP2/ERF genes across the twelve chromosomes of eggplant. Expression profiles of sixteen selected AP2/ERF genes response to low temperature, drought, salt, abscisic acid, and ethylene treatments were analyzed, which revealed the involvement of SmAP2/ERF genes in diverse signaling pathways. In addition, we integrated RNA-Seq data on anthocyanin biosynthesis in eggplant with yeast one-hybrid and dual-luciferase assays and identified involvement of the SmAP2/ERF genes (Smechr0902114.1 and Smechr1102075.1) in the regulation of anthocyanin biosynthesis. This study will enable further functional characterization of AP2/ERF genes in eggplant and extend the current understanding of the role played by AP2/ERF genes in anthocyanin biosynthesis regulation.

Transcription factor SmSPL7 promotes anthocyanin accumulation and negatively regulates phenolic acid biosynthesis in Salvia miltiorrhiza

Plant-specific SQUAMOSA promoter-binding protein-like (SPL) transcription factors play critical regulatory roles during plant growth and development. However, the functions of SPLs in Salvia miltiorrhiza (SmSPLs; a model medicinal plant) have not been reported. Here, the expression patterns and functions of SmSPL7 were characterized in S. miltiorrhiza. SmSPL7 was expressed in all parts of S. miltiorrhiza, with the highest expression level in the leaves, and could be inhibited by multiple hormones, including methyl jasmonate, auxin, abscisic acid, and gibberellin. SmSPL7 is localized within the nucleus and exhibits robust transcriptional activation activity. Transgenic lines overexpressing SmSPL7 demonstrated pronounced growth inhibition, accompanied by increased anthocyanin accumulation via the genetic activation of the anthocyanin biosynthesis pathway. However, SmSPL7 overexpression significantly decreased salvianolic acid B (SalB) production by inhibiting the transcripts of genes implicated in its biosynthesis pathway. Further analysis indicated that SmSPL7 directly binds to SmTAT1 and Sm4CL9 promoters and blocks their expression to inhibit the biosynthesis of SalB. Taken together, these results indicate that SmSPL7 is a negative regulator of SalB biosynthesis but positively regulates anthocyanin accumulation in S. miltiorrhiza. These findings provide new insights into the functionality of the SPL family while establishing an important foundation for further uncovering the crucial roles of SmSPL7 in the growth of S. miltiorrhiza.

The ERF-VII transcription factor SmERF73 coordinately regulates tanshinone biosynthesis in response to stress elicitors in Salvia miltiorrhiza

Here, we investigate the role of SmERF73, a group VII ETHYLENE RESPONSE FACTOR stress response transcription factor, in the regulation of post-modification of the skeleton precursors of diterpene tanshinones in Salvia miltiorrhiza. Most genes found to be involved in tanshinone biosynthesis are located on chromosome 6, and five of these genes comprise a large gene cluster in S. miltiorrhiza. We found that SmERF73 overexpression in S. miltiorrhiza coordinately up-regulated the transcription of seven tanshinone biosynthetic genes, four of which were located in the tanshinone gene cluster, consequently increasing tanshinone accumulation, while SmERF73 silencing reduced corresponding gene transcription and tanshinone accumulation. SmERF73 recognizes GCC-box promoter elements of four tanshinone-associated genes (DXR1, CPS1, KSL1 and CYP76AH3) and activates their expression. Moreover, SmERF73 and its targets were up-regulated by stress elicitors; SmERF73 appears to be at least partly mediated by the jasmonic acid (JA) signaling pathway via interaction with SmJAZ3. SmERF73 coordinately regulates tanshinone biosynthetic gene expression, suggesting a potential link between tanshinone production and plant stress responses.

The basic helix-loop-helix transcription factor TabHLH1 increases chlorogenic acid and luteolin biosynthesis in Taraxacum antungense Kitag

Polyphenols are the main active components of the anti-inflammatory compounds in dandelion, and chlorogenic acid (CGA) is one of the primary polyphenols. However, the molecular mechanism underlying the transcriptional regulation of CGA biosynthesis remains unclear. Hydroxycinnamoyl-CoA:quinate hydroxycinnamoyl transferase (HQT2) is the last rate-limiting enzyme in chlorogenic acid biosynthesis in Taraxacum antungense. Therefore, using the TaHQT2 gene promoter as a probe, a yeast one-hybrid library was performed, and a basic helix-loop-helix (bHLH) transcription factor, TabHLH1, was identified that shared substantial homology with Gynura bicolor DC bHLH1. The TabHLH1 transcript was highly induced by salt stress, and the TabHLH1 protein was localized in the nucleus. CGA and luteolin concentrations in TabHLH1-overexpression transgenic lines were significantly higher than those in the wild type, while CGA and luteolin concentrations in TabHLH1-RNA interference (RNAi) transgenic lines were significantly lower. Quantitative real-time polymerase chain reaction demonstrated that overexpression and RNAi of TabHLH1 in T. antungense significantly affected CGA and luteolin concentrations by upregulating or downregulating CGA and luteolin biosynthesis pathway genes, especially TaHQT2, 4-coumarate-CoA ligase (Ta4CL), chalcone isomerase (TaCHI), and flavonoid-3'-hydroxylase (TaF3'H). Dual-luciferase, yeast one-hybrid, and electrophoretic mobility shift assays indicated that TabHLH1 directly bound to the bHLH-binding motifs of proTaHQT2 and proTa4CL. This study suggests that TabHLH1 participates in the regulatory network of CGA and luteolin biosynthesis in T. antungense and might be useful for metabolic engineering to promote plant polyphenol biosynthesis.

SmSPL6 Induces Phenolic Acid Biosynthesis and Affects Root Development in Salvia miltiorrhiza

Salvia miltiorrhiza is a renowned model medicinal plant species for which 15 SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) family genes have been identified; however, the specific functions of SmSPLs have not been well characterized as of yet. For this study, the expression patterns of SmSPL6 were determined through its responses to treatments of exogenous hormones, including indole acetic acid (IAA), gibberellic acid (GA₃), methyl jasmonic acid (MeJA), and abscisic acid (ABA). To characterize its functionality, we obtained SmSPL6-ovexpressed transgenic S. miltiorrhiza plants and found that overexpressed SmSPL6 promoted the accumulation of phenolic acids and repressed the biosynthesis of anthocyanin. Meanwhile, the root lengths of the SmSPL6-overexpressed lines were significantly longer than the control; however, both the fresh weights and lateral root numbers decreased. Further investigations indicated that SmSPL6 regulated the biosynthesis of phenolic acid by directly binding to the promoter regions of the enzyme genes Sm4CL9 and SmCYP98A14 and activated their expression. We concluded that SmSPL6 regulates not only the biosynthesis of phenolic acids, but also the development of roots in S. miltiorrhiza.

Mechanism by which salt stress induces physiological responses and regulates tanshinone synthesis

Salvia miltiorrhiza is a traditional Chinese herbal medicine with tanshinone as one of the main bioactive components and has antitumor, antibacterial, anti-inflammatory properties, as well as other physiological functions. Tanshinone, as a secondary metabolite, is synthesized under salt stress or other environmental stresses. Oxidative stress is an important physiological response of plants to salt stress. Transcription factors (TFs) are believed to play regulatory roles in this process, and AP2/ERF TFs have significant effects on defense against the adversity of plants. However, investigations on the regulation of AP2/ERF TFs in tanshinone synthesis under salt stress are limited. In this research, the tanshinone content, related gene expression and activities of enzymes, and the markers of oxidative stress were determined. The results showed that SmAP1, SmAP2 and SmERF2 were AP2/ERF TFs with AP conserved sequences, whose relative expression levels increased and were positively correlated with the contents of tanshinone I (T-I), tanshinone IIA (T-IIA) and cryptotanshinone (CT) in the roots of Salvia miltiorrhiza. The content of malondialdehyde (MDA) and the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) increased in the roots of Salvia miltiorrhiza. The expression levels of genes encoding enzymes and the activities of key enzymes in the tanshinone biosynthesis pathway increased accordingly. The results showed that AP2/ERF TFs could positively regulate the biosynthesis of tanshinone in the roots of Salvia miltiorrhiza under salt stress.

Transcriptional Factor-Mediated Regulation of Active Component Biosynthesis in Medicinal Plants

Plants produce thousands of chemically diverse secondary metabolites, many of which have valuable pharmaceutical properties. There is much interest in the synthesis of these pharmaceuticallyvaluable compounds, including the key enzymes and the transcription factors involved. The function and regulatory mechanism of transcription factors in biotic and abiotic stresses have been studied in depth. However, their regulatory roles in the biosynthesis of bioactive compounds, especially in medicinal plants, have only begun. Here, we review what is currently known about how transcription factors contribute to the synthesis of bioactive compounds (alkaloids, terpenoids, flavonoids, and phenolic acids) in medicinal plants. Recent progress has been made in the cloning and characterization of transcription factors in medicinal plants on the genome scale. So far, several large transcription factors have been identified in MYB, WRKY, bHLH, ZIP, AP2/ERF transcription factors. These transcription factors have been predicted to regulate bioactive compound production. These transcription factors positively or negatively regulate the expression of multiple genes encoding key enzymes, and thereby control the metabolic flow through the biosynthetic pathway. Although the research addressing this niche topic is in its infancy, significant progress has been made, and advances in high-throughput sequencing technology are expected to accelerate the discovery of key regulatory transcription factors in medicinal plants. This review is likely to be useful for those interested in the synthesis of pharmaceutically- valuable plant compounds, especially those aiming to breed or engineer plants that produce greater yields of these compounds.

SmKFB5 protein regulates phenolic acid biosynthesis by controlling the degradation of phenylalanine ammonia-lyase in Salvia miltiorrhiza

Phenolic acids are the major secondary metabolites and significant bioactive constituents of the medicinal plant Salvia miltiorrhiza. Many enzyme-encoding genes and transcription factors involved in the biosynthesis of phenolic acids have been identified, but the underlying post-translational regulatory mechanisms are poorly understood. Here, we demonstrate that the S. miltiorrhiza Kelch repeat F-box protein SmKFB5 physically interacts with three phenylalanine ammonia-lyase (PAL) isozymes and mediates their proteolytic turnover via the ubiquitin-26S proteasome pathway. Disturbing the expression of SmKFB5 reciprocally affected the abundance of SmPAL protein and the accumulation of phenolic acids, suggesting that SmKFB5 is a post-translational regulator responsible for the turnover of PAL and negatively controlling phenolic acids. Furthermore, we discovered that treatment of the hairy root of S. miltiorrhiza with methyl jasmonate suppressed the expression of SmKFB5 while inducing the transcription of SmPAL1 and SmPAL3. These data suggested that methyl jasmonate consolidated both transcriptional and post-translational regulation mechanisms to enhance phenolic acid biosynthesis. Taken together, our results provide insights into the molecular mechanisms by which SmKFB5 mediates the regulation of phenolic acid biosynthesis by jasmonic acid, and suggest valuable targets for plant breeders in tailoring new cultivars.

Impact of Traditional Plants and their Secondary Metabolites in the Discovery of COVID-19 Treatment

BACKGROUND

Coronavirus Disease-2019 belongs to the family of viruses which cause serious pneumonia along with fever, breathing issues and infection of lungs, and was first reported in China and later spread worldwide.

OBJECTIVE

Several studies and clinical trials have been conducted to identify potential drugs and vaccines for Coronavirus Disease-2019. The present study listed natural secondary metabolites identified from plant sources with antiviral properties and could be a safer and tolerable treatment for Coronavirus Disease-2019.

METHODS

A comprehensive search on the reported studies was conducted using different search engines such as Google Scholar, SciFinder, Sciencedirect, Medline PubMed, and Scopus for the collection of research articles based on plant-derived secondary metabolites, herbal extracts, and traditional medicine for coronavirus infections.

RESULTS

Status of COVID-19 worldwide and information of important molecular targets involved in COVID- 19 are described, and through literature search, it is highlighted that numerous plant species and their extracts possess antiviral properties and are studied with respect to coronavirus treatments. Chemical information, plant source, test system type with a mechanism of action for each secondary metabolite are also mentioned in this review paper.

CONCLUSION

The present review has listed plants that have presented antiviral potential in the previous coronavirus pandemics and their secondary metabolites, which could be significant for the development of novel and a safer drug which could prevent and cure coronavirus infection worldwide.

Proteomic reveals the influences of smoke-water and karrikinolide on the biosynthesis of salvianolic acids and lignins in Salvia miltiorrhiza hairy roots

The proteins related to the biosynthesis of salvianolic acids and lignins were regulated by smoke-water and karrikinolide in Salvia miltiorrhiza hairy roots. The effects of smoke-water (SW) and karrikinolide (KAR₁) on the biosynthesis of salvianolic acids and lignins in Salvia miltiorrhiza hairy roots have been studied using proteomic technology. The results showed that a total of 1290 and 1678 differentially expressed proteins were respectively obtained in SW and KAR₁ comparing to the control. Bioinformatics analysis indicated the differentially expressed proteins responding to SW and KAR₁ treatments mainly involved in macromolecule metabolic process, cell part, binding, etc., and most of the proteins were located at the cytoplasm and cell membrane, followed by nuclear. In addition, the proteins involved in salvianolic acids biosynthesis were up-regulated, including 4-coumarate-CoA ligase (EC 6.2.1.12) and shikimate O-hydroxycinnamoyl-transferase (EC 2.3.1.133). Enzymes involved in lignins biosynthesis were also identified, e.g. cinnamyl-alcohol dehydrogenase (EC 1.1.1.195) and peroxidase (EC 1.11.1.7). The results indicated that proteins related to the biosynthesis of salvianolic acids and lignins were regulated by SW and KAR₁ in S. miltiorrhiza hairy roots. This study will enhance our understanding of the mechanism by which SW and KAR₁ on the biosynthesis of salvianolic acids and lignins in S. miltiorrhiza hairy roots.

Plasma Membrane H+-ATPase SmPHA4 Negatively Regulates the Biosynthesis of Tanshinones in Salvia miltiorrhiza

Salvia miltiorrhiza Bunge has been widely used in the treatment of cardiovascular and cerebrovascular diseases, due to the pharmacological action of its active components such as the tanshinones. Plasma membrane (PM) H⁺-ATPase plays key roles in numerous physiological processes in plants. However, little is known about the PM H⁺-ATPase gene family in S. miltiorrhiza (Sm). Here, nine PM H⁺-ATPase isoforms were identified and named SmPHA1-SmPHA9. Phylogenetic tree analysis showed that the genetic distance of SmPHAs was relatively far in the S. miltiorrhiza PM H⁺-ATPase family. Moreover, the transmembrane structures were rich in SmPHA protein. In addition, SmPHA4 was found to be highly expressed in roots and flowers. HPLC revealed that accumulation of dihydrotanshinone (DT), cryptotanshinone (CT), and tanshinone I (TI) was significantly reduced in the SmPHA4-OE lines but was increased in the SmPHA4-RNAi lines, ranging from 2.54 to 3.52, 3.77 to 6.33, and 0.35 to 0.74 mg/g, respectively, suggesting that SmPHA4 is a candidate regulator of tanshinone metabolites. Moreover, qRT-PCR confirmed that the expression of tanshinone biosynthetic-related key enzymes was also upregulated in the SmPHA4-RNAi lines. In summary, this study highlighted PM H⁺-ATPase function and provided new insights into regulatory candidate genes for modulating secondary metabolism biosynthesis in S. miltiorrhiza.

Genome-wide analysis of AP2/ERF superfamily in lotus (Nelumbo nucifera) and the association between NnADAP and rhizome morphology

Background

The AP2/ERF family is widely present in plants and plays a crucial regulatory role in plant growth and development. As an essential aquatic horticultural model plant, lotus has an increasingly prominent economic and research value.

Results

We have identified and analysed the AP2/ERF gene family in the lotus. Initially, 121 AP2/ERF family genes were identified. By analysing their gene distribution and protein structure, and their expression patterns during the development of lotus rhizome, combined with previous studies, we obtained an SNP (megascaffold_20:3578539) associated with lotus rhizome phenotype. This SNP was in the NnADAP gene of the AP2 subfamily, and the changes in SNP (C/T) caused amino acid conversion (proline/leucine). We constructed a population of 95 lotus varieties for SNP verification. Through population typing experiments, we found that the group with SNP CC had significantly larger lotus rhizome and higher soluble sugar content among the population.

Conclusions

In conclusion, we speculate that the alteration of the SNP in the NnADAP can affect the size and sugar content of the lotus rhizome.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07473-w.

Transcription Factor: A Powerful Tool to Regulate Biosynthesis of Active Ingredients in Salvia miltiorrhiza

Salvia miltiorrhiza Bunge is a common Chinese herbal medicine, and its major active ingredients are phenolic acids and tanshinones, which are widely used to treat vascular diseases. However, the wild form of S. miltiorrhiza possess low levels of these important pharmaceutical agents; thus, improving their levels is an active area of research. Transcription factors, which promote or inhibit the expressions of multiple genes involved in one or more biosynthetic pathways, are powerful tools for controlling gene expression in biosynthesis. Several families of transcription factors have been reported to participate in regulating phenolic acid and tanshinone biosynthesis and influence their accumulation. This review summarizes the current status in this field, with focus on the transcription factors which have been identified in recent years and their functions in the biosynthetic regulation of phenolic acids and tanshinones. Otherwise, the new insight for further research is provided. Finally, the application of the biosynthetic regulation of active ingredients by the transcription factors in S. miltiorrhiza are discussed, and new insights for future research are explored.