SmMYC2a and SmMYC2b played similar but irreplaceable roles in regulating the biosynthesis of tanshinones and phenolic acids in Salvia miltiorrhiza

The SmMYC2-SmMYB36 complex is involved in methyl jasmonate-mediated tanshinones biosynthesis in Salvia miltiorrhiza

The jasmonic acid (JA) signaling pathway plays an important role in promoting the biosynthesis of tanshinones. While individual transcription factors have been extensively studied in the context of tanshinones biosynthesis regulation, the influence of methyl jasmonate (MeJA)-induced transcriptional complexes remains unexplored. This study elucidates the positive regulatory role of the basic helix-loop-helix protein SmMYC2 in tanshinones biosynthesis in Salvia miltiorrhiza. SmMYC2 not only binds to SmGGPPS1 promoters, activating their transcription, but also interacts with SmMYB36. This interaction enhances the transcriptional activity of SmMYC2 on SmGGPPS1, thereby promoting tanshinones biosynthesis. Furthermore, we identified three JA signaling repressors, SmJAZ3, SmJAZ4, and SmJAZ8, which interact with SmMYC2. These repressors hindered the transcriptional activity of SmMYC2 on SmGGPPS1 and disrupted the interaction between SmMYC2 and SmMYB36. MeJA treatment triggered the degradation of SmJAZ3 and SmJAZ4, allowing the SmMYC2-SmMYB36 complex to subsequently activate the expression of SmGGPPS1, whereas SmJAZ8 inhibited MeJA-mediated degradation due to the absence of the LPIARR motif. These results demonstrate that the SmJAZ-SmMYC2-SmMYB36 module dynamically regulates the JA-mediated accumulation of tanshinones. Our results reveal a new regulatory network for the biosynthesis of tanshinones. This study provides valuable insight for future research on MeJA-mediated modulation of tanshinones biosynthesis.

A high-efficient protoplast transient system for screening gene editing elements in Salvia miltiorrhiza

KEY MESSAGE

A high-efficiency protoplast transient system was devised to screen genome editing elements in Salvia miltiorrhiza. Medicinal plants with high-value pharmaceutical ingredients have attracted research attention due to their beneficial effects on human health. Cell wall-free protoplasts of plants can be used to evaluate the efficiency of genome editing mutagenesis. The capabilities of gene editing in medicinal plants remain to be fully explored owing to their complex genetic background and shortfall of suitable transformation. Here, we took the Salvia miltiorrhiza as a representative example for developing a method to screen favorable gene editing elements with high editing efficiency in medical plants by a PEG-mediated protoplast transformation. Results indicated that using the endogenous SmU6.1 of S. miltiorrhiza to drive sgRNA and the plant codon-optimized Cas9 driven by the promoter SlEF1α can enhance the efficiency of editing. In summary, we uncover an efficacious transient method for screening editing elements and shed new light on increasing gene editing efficiency in medicinal plants.

Integrative effects of phytohormones in the phenolic acids production in Salvia verticillata L. under multi-walled carbon nanotubes and methyl jasmonate elicitation

Salvia verticillata L. is a well-known herb rich in rosmarinic acid (RA) and with therapeutic values. To better understand the possible roles of phytohormones in the production of phenolic acids in S. verticillata, in this work, we investigated some physiological and biochemical responses of the species to methyl jasmonate (MJ) and multi-walled carbon nanotubes (MWCNTs) as two effective elicitors. The leaves were sprayed with aqueous solutions containing 100 mg L-1 MWCNTs and 100 µM MJ and then harvested during interval times of exposure up to 96 h. The level of abscisic acid, as the first effective phytohormone, was altered in the leaves in response to MJ and MWCNTs elicitation (2.26- and 3.06-fold more than the control, respectively), followed by significant increases (P ˂ 0.05) detected in jasmonic acid and salicylic acid contents up to 8 h after exposure. Obtained data revealed that simultaneously with changes in phytohormone profiles, significant (P ˂ 0.05) rises were observed in the content of H2O2 (8.85- and 9.74-folds of control), and the amount of lipid peroxidation (10.18- and 17.01-folds of control) during the initial times after exposure to MJ and MWCNTs, respectively. Later, the content of phenolic acids increased in the elicited leaves due to changes in the transcription levels of key enzymes involved in their biosynthesis pathways, so 2.71- and 11.52-fold enhances observed in the RA content of the leaves after exposure to MJ and MWCNTs, respectively. It is reasonable to conclude that putative linkages between changes in some phytohormone pools lead to the accumulation of phenolic acids in the leaves of S. verticillata under elicitation. Overall, the current findings help us improve our understanding of the signal transduction pathways of the applied stimuli that led to enhanced secondary metabolite production 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.

Jasmonates Coordinate Secondary with Primary Metabolism

Jasmonates (JAs), including jasmonic acid (JA), its precursor 12-oxo-phytodienoic acid (OPDA) and its derivatives jasmonoyl-isoleucine (JA-Ile), methyl jasmonate (MeJA), cis-jasmone (CJ) and other oxylipins, are important in the regulation of a range of ecological interactions of plants with their abiotic and particularly their biotic environments. Plant secondary/specialized metabolites play critical roles in implementing these ecological functions of JAs. Pathway and transcriptional regulation analyses have established a central role of JA-Ile-mediated core signaling in promoting the biosynthesis of a great diversity of secondary metabolites. Here, we summarized the advances in JAs-induced secondary metabolites, particularly in secondary metabolites induced by OPDA and volatile organic compounds (VOCs) induced by CJ through signaling independent of JA-Ile. The roles of JAs in integrating and coordinating the primary and secondary metabolism, thereby orchestrating plant growth-defense tradeoffs, were highlighted and discussed. Finally, we provided perspectives on the improvement of the adaptability and resilience of plants to changing environments and the production of valuable phytochemicals by exploiting JAs-regulated secondary metabolites.

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.

Regulation of the regulators: Transcription factors controlling biosynthesis of plant secondary metabolites during biotic stresses and their regulation by miRNAs

Biotic stresses threaten to destabilize global food security and cause major losses to crop yield worldwide. In response to pest and pathogen attacks, plants trigger many adaptive cellular, morphological, physiological, and metabolic changes. One of the crucial stress-induced adaptive responses is the synthesis and accumulation of plant secondary metabolites (PSMs). PSMs mitigate the adverse effects of stress by maintaining the normal physiological and metabolic functioning of the plants, thereby providing stress tolerance. This differential production of PSMs is tightly orchestrated by master regulatory elements, Transcription factors (TFs) express differentially or undergo transcriptional and translational modifications during stress conditions and influence the production of PSMs. Amongst others, microRNAs, a class of small, non-coding RNA molecules that regulate gene expression post-transcriptionally, also play a vital role in controlling the expression of many such TFs. The present review summarizes the role of stress-inducible TFs in synthesizing and accumulating secondary metabolites and also highlights how miRNAs fine-tune the differential expression of various stress-responsive transcription factors during biotic stress.

SmJAZ4 interacts with SmMYB111 or SmMYC2 to inhibit the synthesis of phenolic acids in Salvia miltiorrhiza

Jasmonic acid (JA), as an important plant hormone, can induce the synthesis of phenolic acids in Salvia miltiorrhiza Bunge, a model medicinal plant, but the specific mechanism remains to be further elucidated. JA-responsive SmMYB111 positively regulates the biosynthesis of salvianolic acid B (SalB), but the molecular mechanism is unclear. Here, we found that SmMYB111 directly binds to the promoters of SmTAT1 and SmCYP98A14 and activates their transcription. Yeast two hybrid and bimolecular fluorescent complementation assay indicated that SmMYB111 interacts with SmJAZ4. Furthermore, we systematically characterized the function of SmJAZ4, which was highly expressed in flowers and roots and located in the nucleus and cell membrane. The contents of phenolic acids in the SmJAZ4-overexpressed transgenic plantlets and SmJAZ4-overexpressed transgenic hairy roots decreased significantly. SmJAZ4 interacts with SmMYC2 or SmMYB111 to repress their transcriptional activation activity on target enzyme genes of the biosynthesis pathway of phenolic acids. Overall, the molecular mechanism of SmJAZ4-SmMYC2/SmMYB111 module participating in JA signaling regulation of SalB biosynthesis was elucidated, which give a clue for the molecular regulation of phenolic acids biosynthesis in S. miltiorrhiza.

A tracking work on how Sm4CL2 re-directed the biosynthesis of salvianolic acids and tanshinones in Salvia miltiorrhiza hairy roots

Overexpression and antisense expression of Sm4CL2 re-directed the biosynthesis of salvianolic acids and tanshinones in Salvia miltiorrhiza hairy roots. Danshen (Salvia miltiorrhiza Bunge) is a widely used traditional Chinese medicine and its main active ingredients are water-soluble phenolic acids and lipophilic diterpenoids which are produced through the phenylpropanoid pathway and terpenoid pathway, respectively. 4-Coumaric acid: Coenzyme A ligase (4CL) is a key enzyme in the phenylpropanoid metabolism. We had obtained Sm4CL2-overexpressing (Sm4CL2-OE) and antisense Sm4CL2-expressing (anti-Sm4CL2) danshen hairy roots over ten years ago. In the follow-up study, we found that total salvianolic acids in Sm4CL2-OE-4 hairy roots increased to 1.35 times of the control-3, and that in anti-Sm4CL2-1 hairy roots decreased to 37.32% of the control-3, but tanshinones in anti-Sm4CL2-1 was accumulated to 1.77 ± 0.16 mg/g of dry weight, compared to undetectable in Sm4CL2-OE-4 and the control-3 hairy roots. Interestingly, Sm4CL2-OE-4 hairy roots contained more lignin, 1.36 times of the control-3, and enhanced cell wall and xylem lignification. Transcriptomic analysis revealed that overexpression of Sm4CL2 caused the upregulation of other phenylpropanoid pathway genes and antisense Sm4CL2 expression resulted in the downregulation of other phenylpropanoid pathway genes but activated the expression of terpenoid pathway genes like SmCYP76AK5, SmGPPS.SSUII.1 and SmDXS2. Protein-protein interaction analysis suggested that Sm4CL2 might interact with PAL, PAL4, CSE, CCoAOMT and SmCYP84A60, and appeared to play a key role in the interaction network. The tracking work in this study proved that Sm4CL2 could redirect both salvianolic acids and tanshinones biosynthesis possibly through synergistically regulating other pathway genes. It also indicated that genetic modification of plant secondary metabolism with biosynthetic gene might cause other responses through protein-protein interactions.

A jasmonate-responsive bHLH transcription factor TaMYC2 positively regulates triterpenes biosynthesis in Taraxacum antungense Kitag

Dandelion is a well-known traditional medical herb, also used as functional food. Dandelion possesses many medical properties, such as anti-bacterial and antioxidant activity and contains a variety of triterpenes, such as α-amyrin, β-amyrin, taraxerol and taraxasterol. In this study, we found that triterpenes biosynthesis was promoted by methyl jasmonate (MeJA), while the transcriptional mechanism underlying triterpenes biosynthesis was rarely investigated. Here, a MeJA-induced bHLH transcription factor TaMYC2 was identified. The content of taraxasterol and taraxerol in dandelion was obviously enhanced in overexpression TaMYC2 transgenic lines and expression level of the squalene synthase gene (TaSS) was elevated to about 3-5 folds compared with the control lines. Dual-LUC, Y1H and EMSA experiments revealed that TaMYC2 bound to the E-box motif in the promoter of TaSS and activated its transcription. Taken together, this study suggested that TaMYC2 acted as a positive regulator for bioengineering approaches to produce high content triterpenes-producing dandelions.

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.

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.

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.

Basic Helix-Loop-Helix Transcription Factors AabHLH2 and AabHLH3 Function Antagonistically With AaMYC2 and Are Negative Regulators in Artemisinin Biosynthesis

Plants have evolved sophisticated systems for regulating the biosynthesis of specialized phytochemicals. Artemisinin, which is a sesquiterpene lactone widely used in anti-malaria treatment, is produced by the Artemisia annua L. plant. However, the artemisinin content in A. annua is low and difficult to meet market demands. Studies have shown that artemisinin biosynthesis in A. annua has complex temporal and spatial specificity and is under tightly transcriptional regulation. However, the mechanism of transcriptional regulation of artemisinin biosynthesis remains unclear. In this study, we identified two MYC-type bHLH transcription factors (AabHLH2 and AabHLH3) as novel regulators of artemisinin biosynthesis. These bHLH TFs act as transcription repressors and function redundantly to negatively regulate artemisinin biosynthesis. Furthermore, AabHLH2 and AabHLH3 are nuclear proteins that bind to DNA elements with similar specificity to that of AaMYC2, but lack the conserved activation domain, suggesting that repression is achieved by competition for the same cis-regulatory elements. Together, our findings reveal a novel artemisinin biosynthesis regulatory network, provide new insight into how specialized metabolites are modulated in plants, and propose a model in which different bHLH TFs coordinated in regulating artemisinin production in the plant. Finally, this study provides some useful target genes for metabolic engineering of artemisinin production via CRISPR/Cas9 gene editing.

Alternative splicing of CsJAZ1 negatively regulates flavan-3-ol biosynthesis in tea plants

Flavan-3-ols are abundant in the tea plant (Camellia sinensis) and confer tea with flavor and health benefits. We recently found that alternative splicing of genes is likely involved in the regulation of flavan-3-ol biosynthesis; however, the underlying regulatory mechanisms remain unknown. Here, we integrated metabolomics and transcriptomics to construct metabolite-gene networks in tea leaves, collected over five different months and from five spatial positions, and found positive correlations between endogenous jasmonic acid (JA), flavan-3-ols, and numerous transcripts. Transcriptome mining further identified CsJAZ1, which is negatively associated with flavan-3-ols formation and has three CsJAZ1 transcripts, one full-length (CsJAZ1-1), and two splice variants (CsJAZ1-2 and -3) that lacked 3' coding sequences, with CsJAZ1-3 also lacking the coding region for the Jas domain. Confocal microscopy showed that CsJAZ1-1 was localized to the nucleus, while CsJAZ1-2 and CsJAZ1-3 were present in both the nucleus and the cytosol. In the absence of JA, CsJAZ1-1 was bound to CsMYC2, a positive regulator of flavan-3-ol biosynthesis; CsJAZ1-2 functioned as an alternative enhancer of CsJAZ1-1 and an antagonist of CsJAZ1-1 in binding to CsMYC2; and CsJAZ1-3 did not interact with CsMYC2. In the presence of JA, CsJAZ1-3 interacted with CsJAZ1-1 and CsJAZ1-2 to form heterodimers that stabilized the CsJAZ1-1-CsMYC2 and CsJAZ1-2-CsMYC2 complexes, thereby repressing the transcription of four genes that act late in the flavan-3-ol biosynthetic pathway. These data indicate that the alternative splicing variants of CsJAZ1 coordinately regulate flavan-3-ol biosynthesis in the tea plant and improve our understanding of JA-mediated flavan-3-ol biosynthesis.

Alternative Splicing Dynamics During the Lifecycle of Salvia miltiorrhiza Root Revealed the Fine Tuning in Root Development and Ingredients Biosynthesis

Alternative splicing (AS) is an essential post-transcriptional process that enhances the coding and regulatory potential of the genome, thereby strongly influencing multiple plant physiology processes, such as metabolic biosynthesis. To explore how AS affects the root development and synthesis of tanshinones and phenolic acid pathways in Salvia miltiorrhiza roots, we investigated the dynamic landscape of AS events in S. miltiorrhiza roots during an annual life history. Temporal profiling represented a distinct temporal variation of AS during the entire development stages, showing the most abundant AS events at the early seedling stage (ES stage) and troughs in 45 days after germination (DAG) and 120 DAG. Gene ontology (GO) analysis indicated that physiological and molecular events, such as lateral root formation, gravity response, RNA splicing regulation, and mitogen-activated protein kinase (MAPK) cascade, were greatly affected by AS at the ES stage. AS events were identified in the tanshinones and phenolic acids pathways as well, especially for the genes for the branch points of the pathways as SmRAS and SmKSL1. Fifteen Ser/Arg-rich (SR) proteins and eight phosphokinases (PKs) were identified with high transcription levels at the ES stage, showing their regulatory roles for the high frequency of AS in this stage. Simultaneously, a co-expression network that includes 521 highly expressed AS genes, SRs, and PKs, provides deeper insight into the mechanism for the variable programming of AS.

Integrated Analysis of Basic Helix Loop Helix Transcription Factor Family and Targeted Terpenoids Reveals Candidate AarbHLH Genes Involved in Terpenoid Biosynthesis in Artemisia argyi

Artemisia argyi is a valuable traditional medicinal plant in Asia. The essential oil from its leaves is rich in terpenoids and has been used to enhance health and well-being. In China, the market scale of industries related to A. argyi has attained tens of billions of Chinese Yuan. The basic helix-loop-helix (bHLH) family is one of the largest transcription factors families in plants that plays crucial roles in diverse biological processes and is an essential regulatory component of terpenoid biosynthesis. However, the bHLH TFs and their regulatory roles in A. argyi remain unknown. Here, 53 AarbHLH genes were identified from the transcriptome of A. argyi and were classified into 15 subfamilies based on the classification of bHLH proteins in Arabidopsis thaliana. The MEME analysis showed that the conserved motif 1 and motif 2 constituted the most conserved bHLH domain and distributed in most AarbHLH proteins. Additionally, integrated analysis of the expression profiles of AarbHLH genes and the contents of targeted terpenoids in different tissues group and JA-treated group were performed. Eleven up-regulated AarbHLHs and one down-regulated AarbHLH were screened as candidate genes that may participate in the regulation of terpenoid biosynthesis (TPS-AarbHLHs). Correlation analysis between gene expression and terpenoid contents indicated that the gene expression of these 12 TPS-AarbHLHs was significantly correlated with the content changes of 1,8-cineole or β-caryophyllene. Protein-protein interaction networks further illustrated that these TPS-AarbHLHs might be involved in terpenoid biosynthesis in A. argyi. This finding provides a basis to further investigate the regulation mechanism of AarbHLH genes in terpenoid biosynthesis, and will be helpful to improve the quality of A. argyi.

Environmental and Genetic Factors Involved in Plant Protection-Associated Secondary Metabolite Biosynthesis Pathways

Plant specialized metabolites (PSMs) play essential roles in the adaptation to harsh environments and function in plant defense responses. PSMs act as key components of defense-related signaling pathways and trigger the extensive expression of defense-related genes. In addition, PSMs serve as antioxidants, participating in the scavenging of rapidly rising reactive oxygen species, and as chelators, participating in the chelation of toxins under stress conditions. PSMs include nitrogen-containing chemical compounds, terpenoids/isoprenoids, and phenolics. Each category of secondary metabolites has a specific biosynthetic pathway, including precursors, intermediates, and end products. The basic biosynthetic pathways of representative PSMs are summarized, providing potential target enzymes of stress-mediated regulation and responses. Multiple metabolic pathways share the same origin, and the common enzymes are frequently to be the targets of metabolic regulation. Most biosynthetic pathways are controlled by different environmental and genetic factors. Here, we summarized the effects of environmental factors, including abiotic and biotic stresses, on PSM biosynthesis in various plants. We also discuss the positive and negative transcription factors involved in various PSM biosynthetic pathways. The potential target genes of the stress-related transcription factors were also summarized. We further found that the downstream targets of these Transcription factors (TFs) are frequently enriched in the synthesis pathway of precursors, suggesting an effective role of precursors in enhancing of terminal products. The present review provides valuable insights regarding screening targets and regulators involved in PSM-mediated plant protection in non-model plants.

The Multifaceted Roles of MYC2 in Plants: Toward Transcriptional Reprogramming and Stress Tolerance by Jasmonate Signaling

Environmental stress is one of the major restrictions on plant development and foodstuff production. The adaptive response in plants largely occurs through an intricate signaling system, which is crucial for regulating the stress-responsive genes. Myelocytomatosis (MYC) transcription factors are the fundamental regulators of the jasmonate (JA) signaling branch that participates in plant development and multiple stresses. By binding to the cis-acting elements of a large number of stress-responsive genes, JA-responsive transcription factors activate the stress-resistant defense genes. The mechanism of stress responses concerns myriad regulatory processes at the physiological and molecular levels. Discovering stress-related regulatory factors is of great value in disclosing the response mechanisms of plants to biotic or abiotic stress, which could guide the genetic improvement of plant resistance. This review summarizes recent researches in various aspects of MYC2-mediated JA signaling and emphasizes MYC2 involvement in plant growth and stress response.

Transcription Factors in Alkaloid Engineering

Plants produce a large variety of low-molecular-weight and specialized secondary compounds. Among them, nitrogen-containing alkaloids are the most biologically active and are often used in the pharmaceutical industry. Although alkaloid chemistry has been intensively investigated, characterization of alkaloid biosynthesis, including biosynthetic enzyme genes and their regulation, especially the transcription factors involved, has been relatively delayed, since only a limited number of plant species produce these specific types of alkaloids in a tissue/cell-specific or developmental-specific manner. Recent advances in molecular biology technologies, such as RNA sequencing, co-expression analysis of transcripts and metabolites, and functional characterization of genes using recombinant technology and cutting-edge technology for metabolite identification, have enabled a more detailed characterization of alkaloid pathways. Thus, transcriptional regulation of alkaloid biosynthesis by transcription factors, such as basic helix–loop–helix (bHLH), APETALA2/ethylene-responsive factor (AP2/ERF), and WRKY, is well elucidated. In addition, jasmonate signaling, an important cue in alkaloid biosynthesis, and its cascade, interaction of transcription factors, and post-transcriptional regulation are also characterized and show cell/tissue-specific or developmental regulation. Furthermore, current sequencing technology provides more information on the genome structure of alkaloid-producing plants with large and complex genomes, for genome-wide characterization. Based on the latest information, we discuss the application of transcription factors in alkaloid engineering.

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.

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.

Multi-omics analysis of the bioactive constituents biosynthesis of glandular trichome in Perilla frutescens

BACKGROUND

Perilla frutescens (L.) Britt is a medicinal and edible plant widely cultivated in Asia. Terpenoids, flavonoids and phenolic acids are the primary source of medicinal ingredients. Glandular trichomes with multicellular structures are known as biochemical cell factories which synthesized specialized metabolites. However, there is currently limited information regarding the site and mechanism of biosynthesis of these constituents in P. frutescens. Herein, we studied morphological features of glandular trichomes, metabolic profiling and transcriptomes through different tissues.

RESULTS

Observation of light microscopy and scanning electron microscopy indicated the presence of three distinct glandular trichome types based on their morphological features: peltate, capitate, and digitiform glandular trichomes. The oil of peltate glandular trichomes, collected by custom-made micropipettes and analyzed by LC-MS and GC-MS, contained perillaketone, isoegomaketone, and egomaketone as the major constituents which are consistent with the components of leaves. Metabolomics and transcriptomics were applied to explore the bioactive constituent biosynthesis in the leaves, stem, and root of P. frutescens. Transcriptome sequencing profiles revealed differential regulation of genes related to terpenoids, flavonoids, and phenylpropanoid biosynthesis, respectively with most genes expressed highly in leaves. The genes affecting the development of trichomes were preliminarily predicted and discussed.

CONCLUSIONS

The current study established the morphological and chemical characteristics of glandular trichome types of P. frutescens implying the bioactive constituents were mainly synthesized in peltate glandular trichomes. The genes related to bioactive constituents biosynthesis were explored via transcriptomes, which provided the basis for unraveling the biosynthesis of bioactive constituents in this popular medicinal plant.

MYC2 Transcription Factors TwMYC2a and TwMYC2b Negatively Regulate Triptolide Biosynthesis in Tripterygium wilfordii Hairy Roots

Triptolide, an important bioactive diterpenoid extracted from the plant Tripterygium wilfordii, exhibits many pharmacological activities. MYC2 transcription factor (TF) plays an important role in the regulation of various secondary metabolites in plants. However, whether MYC2 TF could regulate the biosynthesis of triptolide in T. wilfordii is still unknown. In this study, two homologous MYC2 TF genes, TwMYC2a and TwMYC2b, were isolated from T. wilfordii hairy roots and functionally characterized. The analyses of the phylogenetic tree and subcellular localization showed that they were grouped into the IIIe clade of the bHLH superfamily with other functional MYC2 proteins and localized in the nucleus. Furthermore, yeast one-hybrid and GUS transactivation assays suggested that TwMYC2a and TwMYC2b inhibited the promoter activity of the miltiradiene synthase genes, TwTPS27a and TwTPS27b, by binding to the E-box (CACATG) and T/G-box (CACGTT) motifs in their promoters. Transgenic results revealed that RNA interference of TwMYC2a/b significantly enhanced the triptolide accumulation in hairy roots and liquid medium by upregulating the expression of several key biosynthetic genes, including TwMS (TwTPS27a/b), TwCPS (TwTPS7/9), TwDXR, and TwHMGR1. In summary, our findings show that TwMYC2a and TwMYC2b act as two negative regulators of triptolide biosynthesis in T. wilfordii hairy roots and also provide new insights on metabolic engineering of triptolide in the future.

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.

Genome-Wide Identification of the TIFY Family in Salvia miltiorrhiza Reveals That SmJAZ3 Interacts With SmWD40-170, a Relevant Protein That Modulates Secondary Metabolism and Development

Salvia miltiorrhiza Bunge (S. miltiorrhiza), a traditional Chinese medicinal herb, contains numerous bioactive components with broad range of pharmacological properties. By increasing the levels of endogenous jasmonate (JA) in plants or treating them with methyl jasmonate (MeJA), the level of tanshinones and salvianolic acids can be greatly enhanced. The jasmonate ZIM (JAZ) proteins belong to the TIFY family, and act as repressors, releasing targeted transcriptional factors in the JA signaling pathway. Herein, we identified and characterized 15 TIFY proteins present in S. miltiorrhiza. Quantitative reverse transcription PCR analysis indicated that the JAZ genes were all constitutively expressed in different tissues and were induced by MeJA treatments. SmJAZ3, which negatively regulates the tanshinones biosynthesis pathway in S. miltiorrhiza and the detailed molecular mechanism is poorly understood. SmJAZ3 acts as a bait protein to capture and identify a WD-repeat containing the protein SmWD40-170. Further molecular and genetic analysis revealed that SmWD40-170 is a positive regulator, promoting the accumulation of secondary metabolites in S. miltiorrhiza. Our study systematically analyzed the TIFY family and speculated a module of the JAZ-WD40 complex provides new insights into the mechanisms regulating the biosynthesis of secondary metabolites in S. miltiorrhiza.

An Optimal Combination of Chemically Pure Compounds from Salvia Miltiorrhiza for Inhibiting Cell Proliferation

OBJECTIVE

Salvia Miltiorrhiza (SM) is a traditional Chinese medicine used clinically to treat cardiovascular diseases including atherosclerosis and myocardial infarction. Its therapeutic effect has been confirmed by many clinical and pharmacological studies. However, the optimal formulation of active ingredients in SM for treating cardiovascular diseases remains unclear. In this study, we determined the ratio of the optimal compatibility of SM ingredients DSS, Sal-A, Sal-B, and PAL (SABP）with a uniform and orthogonal optimized experimental design. In addition, we determined the anti-oxidation effect of SABP using Adventitial Fibroblasts (AFs).

METHODS

By using a combination of uniform and orthogonal designs, we determined the optimal formulation of aqueous extract from SM. MTT assay was used to determine the inhibitory effects of these 4 components of SM on the AFs, which were isolated and cultured from aorta. The reactive oxygen species (ROS) production in AFs was compared before and after SABP treatment.

RESULTS

The optimal formulation of these 4 aqueous extracts from SM were 150︰7︰300︰500, and their concentrations were S(1.5×10-4 mol/L), A(7×10-6 mol/L), B(3×10-4 mol/L), and P(5×10-4 mol/L). There were some synergies between these 4 components. Moreover, SABP decreased ROS production in AFs.

CONCLUSION

These findings suggest that SABP inhibits the proliferation and oxidation stress in AFs. The present study provides a new evidence that the efficacy and function generated from optimal formulation of active ingredients in SM are better than lyophilized powder of SM.

The methyl jasmonate-responsive transcription factor SmMYB1 promotes phenolic acid biosynthesis in Salvia miltiorrhiza

Water-soluble phenolic acids are major bioactive compounds in the medicinal plant species Salvia miltiorrhiza. Phenolic acid biosynthesis is induced by methyl jasmonate (MeJA) in this important Chinese herb. Here, we investigated the mechanism underlying this induction by analyzing a transcriptome library of S. miltiorrhiza in response to MeJA. Global transcriptome analysis identified the MeJA-responsive R2R3-MYB transcription factor-encoding gene SmMYB1. Overexpressing SmMYB1 significantly promoted phenolic acid accumulation and upregulated the expression of genes encoding key enzymes in the phenolic acid biosynthesis pathway, including cytochrome P450-dependent monooxygenase (CYP98A14). Dual-luciferase (dual-LUC) assays and/or an electrophoretic mobility shift assays (EMSAs) indicated that SmMYB1 activated the expression of CYP98A14, as well as the expression of genes encoding anthocyanin biosynthesis pathway enzymes, including chalcone isomerase (CHI) and anthocyanidin synthase (ANS). In addition, SmMYB1 was shown to interact with SmMYC2 to additively promote CYP98A14 expression compared to the action of SmMYB1 alone. Taken together, these results demonstrate that SmMYB1 is an activator that improves the accumulation of phenolic acids and anthocyanins in S. miltiorrhiza. These findings lay the foundation for in-depth studies of the molecular mechanism underlying MeJA-mediated phenolic acid biosynthesis and for the metabolic engineering of bioactive ingredients in S. miltiorrhiza.

The methyl jasmonate-responsive transcription factor SmMYB1 promotes phenolic acid biosynthesis in Salvia miltiorrhiza

Water-soluble phenolic acids are major bioactive compounds in the medicinal plant species Salvia miltiorrhiza. Phenolic acid biosynthesis is induced by methyl jasmonate (MeJA) in this important Chinese herb. Here, we investigated the mechanism underlying this induction by analyzing a transcriptome library of S. miltiorrhiza in response to MeJA. Global transcriptome analysis identified the MeJA-responsive R2R3-MYB transcription factor-encoding gene SmMYB1. Overexpressing SmMYB1 significantly promoted phenolic acid accumulation and upregulated the expression of genes encoding key enzymes in the phenolic acid biosynthesis pathway, including cytochrome P450-dependent monooxygenase (CYP98A14). Dual-luciferase (dual-LUC) assays and/or an electrophoretic mobility shift assays (EMSAs) indicated that SmMYB1 activated the expression of CYP98A14, as well as the expression of genes encoding anthocyanin biosynthesis pathway enzymes, including chalcone isomerase (CHI) and anthocyanidin synthase (ANS). In addition, SmMYB1 was shown to interact with SmMYC2 to additively promote CYP98A14 expression compared to the action of SmMYB1 alone. Taken together, these results demonstrate that SmMYB1 is an activator that improves the accumulation of phenolic acids and anthocyanins in S. miltiorrhiza. These findings lay the foundation for in-depth studies of the molecular mechanism underlying MeJA-mediated phenolic acid biosynthesis and for the metabolic engineering of bioactive ingredients in S. miltiorrhiza.

JA-Responsive Transcription Factor SmMYB97 Promotes Phenolic Acid and Tanshinone Accumulation in Salvia miltiorrhiza

Phenolic acids and tanshinones are active principles in Salvia miltiorrhiza Bunge administered for cardiovascular and cerebrovascular diseases. Jasmonic acid (JA) promotes secondary metabolite accumulation, but the regulatory mechanism is unknown in S. miltiorrhiza. We identified and characterized the JA-responsive gene SmMYB97. Multiple sequence alignment and phylogenetic tree analyses showed that SmMYB97 was clustered with AtMYB11, AtMYB12, and ZmP1 in the subgroup S7 regulating flavonol biosynthesis. SmMYB97 was highly expressed in S. miltiorrhiza leaves and induced by methyl jasmonate (MeJA). SmMYB97 was localized in the nucleus and had strong transcriptional activation activity. SmMYB97 overexpression increased phenolic acid and tanshinone biosynthesis and upregulated the genes implicated in these processes. Yeast one-hybrid and transient transcriptional activity assays disclosed that SmMYB97 binds the PAL1, TAT1, CPS1, and KSL1 promoter regions. SmJAZ8 interacts with SmMYB97 and downregulates the genes that it controls. This study partially clarified the regulatory network of MeJA-mediated secondary metabolite biosynthesis in S. miltiorrhiza.

Integrative omic and transgenic analyses reveal the positive effect of ultraviolet-B irradiation on salvianolic acid biosynthesis through upregulation of SmNAC1

Salvianolic acids (SalAs), a group of secondary metabolites in Salvia miltiorrhiza, are widely used for treating cerebrovascular diseases. Their biosynthesis is modulated by a variety of abiotic factors, including ultraviolet-B (UV-B) irradiation; however, the underlying mechanisms remain largely unknown. Here, an integrated metabolomic, proteomic, and transcriptomic approach coupled with transgenic analyses was employed to dissect the mechanisms underlying UV-B irradiation-induced SalA biosynthesis. Results of metabolomics showed that 28 metabolites, including 12 SalAs, were elevated in leaves of UV-B-treated S. miltiorrhiza. Meanwhile, the contents of several phytohormones, including jasmonic acid and salicylic acid, which positively modulate the biosynthesis of SalAs, also increased in UV-B-treated S. miltiorrhiza. Consistently, 20 core biosynthetic enzymes and numerous transcription factors that are involved in SalA biosynthesis were elevated in treated samples as indicated by a comprehensive proteomic analysis. Correlation and gene expression analyses demonstrated that the NAC1 gene, encoding a NAC transcriptional factor, was positively involved in UV-B-induced SalA biosynthesis. Accordingly, overexpression and RNA interference of NAC1 increased and decreased SalA contents, respectively, through regulation of key biosynthetic enzymes. Furthermore, ChIP-qPCR and Dual-LUC assays showed that NAC1 could directly bind to the CATGTG and CATGTC motifs present in the promoters of the SalA biosynthesis-related genes PAL3 and TAT3, respectively, and activate their expression. Our results collectively demonstrate that NAC1 plays a crucial role in UV-B irradiation-induced SalA biosynthesis. Taken together, our findings provide mechanistic insights into the UV-B-induced SalA biosynthesis in S. miltiorrhiza, and shed light on a great potential for the development of SalA-abundant varieties through genetic engineering.

SmMYC2b Enhances Tanshinone Accumulation in Salvia miltiorrhiza by Activating Pathway Genes and Promoting Lateral Root Development

Salvia miltiorrhiza Bunge (Lamiaceae) is an economically important medicinal plant as well as an emerging model plant. Our previous studies indicate that SmMYC2b is a positive transcription factor that can affect the biosynthesis of phenolic acids and tanshinones in S. miltiorrhiza. Moreover, MYC2s are well known to induce the development of lateral roots. As tanshinones are mainly distributed in the periderm, the promotion of lateral root development probably leads to increased accumulation of tanshinones. In this paper, we firstly discovered that SmMYC2b played a dual regulatory role in effectively enhancing the tanshinone accumulation by activating tanshinone biosynthetic pathway and promoting lateral root development. The expression levels of the previously studied pathway genes SmCPS1, SmKSL1, SmCYP76AH1, SmCYP76AH3, and SmCYP76AK1 dramatically increased. In addition, SmMYC2b was proved to exhibit a similar function as other homologs in promoting lateral root development, which increased the tanshinone produced tissue and further enhanced the biosynthesis of tanshinones. RNA-seq assays revealed that SmMYC2b-regulated genes comprised 30.6% (1,901 of 6,210) of JA-responsive genes, confirming that SmMYC2b played a crucial role in transcriptional regulation of JA-regulated genes. Overall, we concluded that SmMYC2b could enhance tanshinone accumulation by activating the tanshinone biosynthetic pathway and promoting lateral root development. Our study provides an effective approach to enhance the production of desired tanshinones and enriches our knowledge of the related regulatory network.

MdMYC2 and MdERF3 Positively Co-Regulate α-Farnesene Biosynthesis in Apple

α-Farnesene, a sesquiterpene volatile compound plays an important role in plant defense and is known to be associated with insect attraction and with superficial scald of apple and pear fruits during cold storage. But the mechanism whereby transcription factors regulate apple α-farnesene biosynthesis has not been clarified. Here, we report that two transcription factors, MdMYC2 and MdERF3 regulated α-farnesene biosynthesis in apple fruit. Dual-luciferase assays and Y1H assays indicated that MdMYC2 and MdERF3 effectively trans-activated the MdAFS promoter. EMSAs showed that MdERF3 directly binds the DRE motif in the MdAFS promoter. Subsequently, overexpression of MdMYC2 and MdERF3 in apple calli markedly activated the transcript levels of MdHMGR2 and MdAFS. Furthermore, transient overexpression of MdMYC2 and MdERF3 in apple fruit significantly increased MdAFS expression and hence, α-farnesene production. These results indicate that MdMYC2 and MdERF3 are positive regulators of α-farnesene biosynthesis and have important value in genetic engineering of α-farnesene production.

bHLH transcription factor SmbHLH92 negatively regulates biosynthesis of phenolic acids and tanshinones in Salvia miltiorrhiza

Objective

Salvia miltiorrhiza is a valuable herbal medicine with tanshinone and phenolic acid as the main biological active ingredients. The biosynthetic regulation of these bioactive compounds is controlled by a set of transcription factors (TFs). The basic helix-loop-helix (bHLH) transcription factor plays an important role in various physiological and biochemical processes in plants. However, research on bHLH TFs regulating phenolic acid or tanshinone biosynthesis in S. miltiorrhiza is limited.

Methods

qRT-PCR was used for gene expression analysis. The subcellular localization of SmbHLH92 was detected by SmbHLH92-GFP transient transformation into tobacco leaves, and its fluorescence was observed using a confocal laser scanning microscope. The transcriptional activity of SmbHLH92 was confirmed in the AH109 yeast strain. RNA interference hairy roots of SmbHLH92-RNAi transgenic lines were obtained through Agrobacterium-mediated genetic transformation. Ultra performance liquid chromatography (UPLC) was used to detect the changes of phenolic acids and tanshinones.

Results

SmbHLH92 is a bHLH transcription factor that is highly expressed in the root and phloem of S. miltiorrhiza. The subcellular localization and transcriptional activity of SmbHLH92 indicated that SmbHLH92 was located in the nucleus and may be a transcription factor. RNA interference (RNAi) of SmbHLH92 in hairy roots of S. miltiorrhiza significantly increased the accumulation of phenolic acid and tanshinone. Quantitative RT-PCR (RT-qPCR) analysis showed the transcription level of genes encoding the key enzymes involved in the phenolic acid and tanshinone biosynthetic pathways was increased in the hairy roots of the SmbHLH92-RNAi transgenic line, comparing with the control line.

Conclusion

These data indicate that SmbHLH92 is a negative regulator involved in the regulation of phenolic acid and tanshinone biosynthesis in S. miltiorrhiza.

SmbHLH53 is relevant to jasmonate signaling and plays dual roles in regulating the genes for enzymes in the pathway for salvianolic acid B biosynthesis in Salvia miltiorrhiza

Basic helix-loop-helix (bHLH) transcription factors play essential roles in myriad regulatory processes, including secondary metabolism. In this study with Salvia miltiorrhiza, we isolated and characterized SmbHLH53, which encodes a bHLH family member. Expression of this gene was significantly induced by wounding and multiple hormones, including methyl jasmonic acid; transcript levels were highest in the leaves and roots. Phylogenetic analysis indicated that SmbHLH53 clusters withAtbHLH17 and AtbHLH13, two negative regulators of jasmonate (JA) responses, and is localized in the nucleus and cell membrane. Yeast two-hybrid and bimolecular fluorescent complementation assays indicated that SmbHLH53 forms a homodimer as well as a heterodimer with SmbHLH37. It also interacts with both SmJAZs1/3/8 and SmMYC2, the core members of the JA signal pathway. Unexpectedly, we noted that overexpression of SmbHLH53 did not significantly influence the concentrations of rosmarinic acid and salvianolic acid B in transgenic plants. Results from yeast one-hybrid assays showed that SmbHLH53 binds to the promoters of SmTAT1, SmPAL1, and Sm4CL9, the key genes for enzymes in the pathway for phenolic acid synthesis. Assays of transient transcriptional activity demonstrated that SmbHLH53 represses the promoter of SmTAT1 while activating the promoter of Sm4CL9. Thus, the present work revealed that SmbHLH53 may play dual roles in regulating the genes for enzymes in the pathway for Sal B biosynthesis.

Systematic Analysis of Kelch Repeat F-box (KFB) Protein Gene Family and Identification of Phenolic Acid Regulation Members in Salvia miltiorrhiza Bunge

S. miltiorrhiza is a well-known Chinese herb for the clinical treatment of cardiovascular and cerebrovascular diseases. Tanshinones and phenolic acids are the major secondary metabolites and significant pharmacological constituents of this plant. Kelch repeat F-box (KFB) proteins play important roles in plant secondary metabolism, but their regulation mechanism in S. miltiorrhiza has not been characterized. In this study, we systematically characterized the S. miltiorrhiza KFB gene family. In total, 31 SmKFB genes were isolated from S. miltiorrhiza. Phylogenetic analysis of those SmKFBs indicated that 31 SmKFBs can be divided into four groups. Thereinto, five SmKFBs (SmKFB1, 2, 3, 5, and 28) shared high homology with other plant KFBs which have been described to be regulators of secondary metabolism. The expression profile of SmKFBs under methyl jasmonate (MeJA) treatment deciphered that six SmKFBs (SmKFB1, 2, 5, 6, 11, and 15) were significantly downregulated, and two SmKFBs (SmKFB22 and 31) were significantly upregulated. Tissue-specific expression analysis found that four SmKFBs (SmKFB4, 11, 16, and 17) were expressed preferentially in aerial tissues, while two SmKFBs (SmKFB5, 25) were predominantly expressed in roots. Through a systematic analysis, we speculated that SmKFB1, 2, and 5 are potentially involved in phenolic acids biosynthesis.

Tanshinone and salvianolic acid biosynthesis are regulated by SmMYB98 in Salvia miltiorrhiza hairy roots

Salvia miltiorrhiza Bunge is an herb rich in bioactive tanshinone and salvianolic acid compounds. It is primarily used as an effective medicine for treating cardiovascular and cerebrovascular diseases. Liposoluble tanshinones and water-soluble phenolic acids are a series of terpenoids and phenolic compounds, respectively. However, the regulation mechanism for the simultaneous promotion of tanshinone and salvianolic acid biosynthesis remains unclear. This study identified a R2R3-MYB subgroup 20 transcription factor (TF), SmMYB98, which was predominantly expressed in S. miltiorrhiza lateral roots. The accumulation of major bioactive metabolites, tanshinones, and salvianolic acids, was improved in SmMYB98 overexpression (OE) hairy root lines, but reduced in SmMYB98 knockout (KO) lines. The qRT-PCR analysis revealed that the transcriptional expression levels of tanshinone and salvianolic acid biosynthesis genes were upregulated by SmMYB98-OE and downregulated by SmMYB98-KO. Dual-Luciferase (Dual-LUC) assays demonstrated that SmMYB98 significantly activated the transcription of SmGGPPS1, SmPAL1, and SmRAS1. These results suggest that SmMYB98-OE can promote tanshinone and salvianolic acid production. The present findings illustrate the exploitation of R2R3-MYB in terpenoid and phenolic biosynthesis, as well as provide a feasible strategy for improving tanshinone and salvianolic acid contents by MYB proteins in S. miltiorrhiza.

The Anticancer Properties of Tanshinones and the Pharmacological Effects of Their Active Ingredients

Cancer is a common malignant disease worldwide with an increasing mortality in recent years. Salvia miltiorrhiza, a well-known traditional Chinese medicine, has been used for the treatment of cardiovascular and cerebrovascular diseases for thousands of years. The liposoluble tanshinones in S. miltiorrhiza are important bioactive components and mainly include tanshinone IIA, dihydrodanshinone, tanshinone I, and cryptotanshinone. Previous studies showed that these four tanshinones exhibited distinct inhibitory effects on tumor cells through different molecular mechanisms in vitro and in vivo. The mechanisms mainly include the inhibition of tumor cell growth, metastasis, invasion, and angiogenesis, apoptosis induction, cell autophagy, and antitumor immunity, and so on. In this review, we describe the latest progress on the antitumor functions and mechanisms of these four tanshinones to provide a deeper understanding of the efficacy. In addition, the important role of tumor immunology is also reviewed.

SmbHLH3 acts as a transcription repressor for both phenolic acids and tanshinone biosynthesis in Salvia miltiorrhiza hairy roots

Phenolic acids and tanshinones are the two groups of pharmaceutically active metabolites in Salvia miltiorrhiza Bunge. Their contents are the key quality indicator to evaluate S. miltiorrhiza. bHLH transcription factors have important roles in regulation of plant specialised metabolism. In this study, an endogenous bHLH transcription factor, SmbHLH3, was identified and functionally analyzed. SmbHLH3 was presented in all the six tissues and mostly expressed in fibrous roots and flowers. It was localized to the nucleus. Overexpression of SmbHLH3 decreased both phenolic acids and tanshinones contents. Contents of caffeic acid and rosmarinic acid were both decreased to 50% of the control. And accumulation of salvianolic acid B was decreased as much as 62%. Content of cryptotanshinone, dihydrotanshinone I, tanshinone I and tanshinone IIA in SmbHLH3-overexpression lines were reduced 97%, 62%, 86% and 91%, respectively. In the transgenic lines, expression of C4H1, TAT and HPPR in phenolic acids pathways were reduced to about 43%, 66% and 77% of the control, respectively. For tanshinone biosynthetic pathways, transcripts of DXS3, DXR, HMGR1, KSL1, CPS1 and CYP76AH1 were reduced to 46%, 65%, 78%, 57%, 27% and 62% of the control, respectively. There was an E/G-box specific binding site in SmbHLH3, which may bind the E/G-box present in promoter region of these biosynthetic pathway genes. Y1H results indicated that SmbHLH3 could bind the promoter of TAT, HPPR, KSL1 and CYP76AH1. These findings indicated that SmbHLH3 downregulate both phenolic acids and tanshinone accumulation through directly suppressing the transcription of key enzyme genes.

Plant Specialized Metabolism Regulated by Jasmonate Signaling

As sessile and autotrophic organisms, plants have evolved sophisticated pathways to produce a rich array of specialized metabolites, many of which are biologically active and function as defense substances in protecting plants from herbivores and pathogens. Upon stimuli, these structurally diverse small molecules may be synthesized or constitutively accumulated. Jasmonate acids (JAs) are the major defense phytohormone involved in transducing external signals (such as wounding) to activate defense reactions, including, in particular, the reprogramming of metabolic pathways that initiate and enhance the production of defense compounds against insect herbivores and pathogens. In this review, we summarize the progress of recent research on the control of specialized metabolic pathways in plants by JA signaling, with an emphasis on the molecular regulation of terpene and alkaloid biosynthesis. We also discuss the interplay between JA signaling and various signaling pathways during plant defense responses. These studies provide valuable data for breeding insect-proof crops and pave the way to engineering the production of valuable metabolites in future.

PatJAZ6 Acts as a Repressor Regulating JA-Induced Biosynthesis of Patchouli Alcohol in Pogostemon Cablin

The JASMONATE ZIM DOMAIN (JAZ) proteins act as negative regulators in the jasmonic acid (JA) signaling pathways of plants, and these proteins have been reported to play key roles in plant secondary metabolism mediated by JA. In this study, we firstly isolated one JAZ from P. cablin, PatJAZ6, which was characterized and revealed based on multiple alignments and a phylogenic tree analysis. The result of subcellular localization indicated that the PatJAZ6 protein was located in the nucleus of plant protoplasts. The expression level of PatJAZ6 was significantly induced by the methyl jasmonate (MeJA). Furthermore, by means of yeast two-hybrid screening, we identified two transcription factors that interact with the PatJAZ6, the PatMYC2b1 and PatMYC2b2. Virus-induced gene silencing (VIGS) of PatJAZ6 caused a decrease in expression abundance, resulting in a significant increase in the accumulation of patchouli alcohol. Moreover, we overexpressed PatJAZ6 in P. cablin, which down-regulated the patchoulol synthase expression, and then suppressed the biosynthesis of patchouli alcohol. The results demonstrate that PatJAZ6 probably acts as a repressor in the regulation of patchouli alcohol biosynthesis, contributed to a model proposed for the potential JA signaling pathway in P. cablin.

Tanshinone production could be increased by the expression of SmWRKY2 in Salvia miltiorrhiza hairy roots

Tanshinones are the main bioactive diterpenes in Salvia miltiorrhiza Bunge, are widely used for treating cardiovascular and cerebrovascular diseases. However, the biosynthetic mechanisms of these compounds have not yet been fully explained. In this study, a transcription factor named SmWRKY2 was isolated and functionally characterized. Multiple sequence analysis indicated it was classified into subgroup I of the WRKY family. Expression pattern showed that SmWRKY2 was mainly expressed in the stem and leaf and was inducible by methyl jasmonate (MeJA) treatment. Subcellular localization showed that SmWRKY2 was localized in the nucleus. Overexpression of SmWRKY2 in S. miltiorrhiza hairy roots significantly increased the expression of SmDXS2 and SmCPS, resulting in increased accumulation of tanshinones and the highest total tanshinone content was detected in OE-SmWRKY2-1 line, which was 1.83 times of the control. Meanwhile, tanshinone production was slightly reduced in the antisense-SmWRKY2 line. Dual-Luciferase assay showed that SmWRKY2 can positively regulate SmDXS2 and SmCPS expression, However, Y1H and EMSA experiments indicate that SmWRKY2 only binds to the W-box of the SmCPS promoter. Our study shows that SmWRKY2 is a positive regulator of tanshinone biosynthesis by mainly activating SmCPS. This study thus sheds new light on the regulatory role of SmWRKY2 in tanshinone biosynthesis.

The AP2/ERF transcription factor SmERF128 positively regulates diterpenoid biosynthesis in Salvia miltiorrhiza

The novel AP2/ERF transcription factor SmERF128 positively regulates diterpenoid tanshinone biosynthesis by activating the expression of SmCPS1, SmKSL1, and SmCYP76AH1 in Salvia miltiorrhiza. Certain members of the APETALA2/ethylene-responsive factor (AP2/ERF) family regulate plant secondary metabolism. Although it is clearly documented that AP2/ERF transcription factors (TFs) are involved in sesquiterpenoid biosynthesis, the regulation of diterpenoid biosynthesis by AP2/ERF TFs remains elusive. Here, we report that the novel AP2/ERF TF SmERF128 positively regulates diterpenoid tanshinone biosynthesis in Salvia miltiorrhiza. Overexpression of SmERF128 increased the expression levels of copalyl diphosphate synthase 1 (SmCPS1), kaurene synthase-like 1 (SmKSL1) and cytochrome P450 monooxygenase 76AH1 (SmCYP76AH1), whereas their expression levels were decreased when SmERF128 was silenced. Accordingly, the content of tanshinone was reduced in SmERF128 RNA interference (RNAi) hairy roots and dramatically increased in SmERF128 overexpression hairy roots, as demonstrated through Ultra Performance Liquid Chromatography (UPLC) and Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) analysis. Furthermore, SmERF128 activated the expression of SmCPS1, SmKSL1, and SmCYP76AH1 by binding to the GCC box, and to the CRTDREHVCBF2 (CBF2) and RAV1AAT (RAA) motifs within their promoters during in vivo and in vitro assays. Our findings not only reveal the molecular basis of how the AP2/ERF transcription factor SmERF128 regulates diterpenoid biosynthesis, but also provide useful information for improving tanshinone production through genetic engineering.

The genome of the medicinal plant Andrographis paniculata provides insight into the biosynthesis of the bioactive diterpenoid neoandrographolide

Andrographis paniculata is a herbaceous dicot plant widely used for its anti-inflammatory and anti-viral properties across its distribution in China, India and other Southeast Asian countries. A. paniculata was used as a crucial therapeutic treatment during the influenza epidemic of 1919 in India, and is still used for the treatment of infectious disease in China. A. paniculata produces large quantities of the anti-inflammatory diterpenoid lactones andrographolide and neoandrographolide, and their analogs, which are touted to be the next generation of natural anti-inflammatory medicines for lung diseases, hepatitis, neurodegenerative disorders, autoimmune disorders and inflammatory skin diseases. Here, we report a chromosome-scale A. paniculata genome sequence of 269 Mb that was assembled by Illumina short reads, PacBio long reads and high-confidence (Hi-C) data. Gene annotation predicted 25 428 protein-coding genes. In order to decipher the genetic underpinning of diterpenoid biosynthesis, transcriptome data from seedlings elicited with methyl jasmonate were also obtained, which enabled the identification of genes encoding diterpenoid synthases, cytochrome P450 monooxygenases, 2-oxoglutarate-dependent dioxygenases and UDP-dependent glycosyltransferases potentially involved in diterpenoid lactone biosynthesis. We further carried out functional characterization of pairs of class-I and -II diterpene synthases, revealing the ability to produce diversified labdane-related diterpene scaffolds. In addition, a glycosyltransferase able to catalyze O-linked glucosylation of andrograpanin, yielding the major active product neoandrographolide, was also identified. Thus, our results demonstrate the utility of the combined genomic and transcriptomic data set generated here for the investigation of the production of the bioactive diterpenoid lactone constituents of the important medicinal herb A. paniculata.

Enhancement of tanshinone production in Salvia miltiorrhiza hairy root cultures by metabolic engineering

BACKGROUND

Tanshinones are diterpenoid compounds that are used to treat cardiovascular diseases. As current extraction methods for tanshinones are inefficient, there is a pressing need to improve the production of these bioactive compounds to meet increasing demand.

RESULTS

Overexpression of SmMDS (2-c-methyl-d-erythritol 2,4-cyclodiphosphate synthase, a tanshinone biosynthesis gene) in transgenic Salvia miltiorrhiza hairy roots significantly increased the tanshinone yield compared to the control, and total tanshinone content in SmMDS-overexpressing lines increased after elicitor treatment. Total tanshinones increased to 2.5, 2.3, and 3.2 mg/g DW (dry weight) following treatment with Ag⁺, YE (yeast extract), and MJ (methyl jasmonate), respectively, compared with the non-induced transgenic line (1.7 mg/g DW). Also, qRT-PCR analysis showed that the expression levels of two pathway genes was positively correlated with increased accumulation of tanshinone.

CONCLUSIONS

Our study provides an effective strategy for increasing the content of tanshinones and other natural compounds using a combination of genetic engineering and elicitor treatment.

SlMYC1 Regulates Type VI Glandular Trichome Formation and Terpene Biosynthesis in Tomato Glandular Cells

Tomato (Solanum lycopersicum) glandular trichomes function as biochemical factories that synthesize a diverse array of specialized metabolites. Terpenoids are the most diverse class of plant specialized metabolites, with volatile mono- and sesquiterpenes playing important roles in plant defense. Although the biosynthetic pathways of volatile terpenes in tomato glandular trichomes have been well described, little is known about their regulation. Here, we demonstrate that SlMYC1, a basic helix-loop-helix transcription factor, differentially regulates mono- and sesquiterpene biosynthesis in the type VI glandular trichomes of tomato leaves and stems. SlMYC1 functions as a positive regulator of monoterpene biosynthesis in both leaf and stem trichomes but as a negative regulator of sesquiterpene biosynthesis in stem trichomes. SlMYC1 is also essential for type VI glandular trichome development, as knocking down SlMYC1 led to the production of smaller type VI glandular trichomes at lower densities, and knocking out this gene led to their absence. Our findings reveal a role for SlMYC1 not only in type VI glandular trichome development but also in the regulation of terpene biosynthesis in tomato.