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

Biotechnological Exploration of Transformed Root Culture for Value-Added Products

Medicinal plants produce valuable secondary metabolites with anticancer, analgesic, anticholinergic or other activities, but low metabolite levels and limited available tissue restrict metabolite yields. Transformed root cultures, also called hairy roots, provide a feasible approach for producing valuable secondary metabolites. Various strategies have been used to enhance secondary metabolite production in hairy roots, including increasing substrate availability, regulating key biosynthetic genes, multigene engineering, combining genetic engineering and elicitation, using transcription factors (TFs), and introducing new genes. In this review, we focus on recent developments in hairy roots from medicinal plants, techniques to boost production of desired secondary metabolites, and the development of new technologies to study these metabolites. We also discuss recent trends, emerging applications, and future perspectives.

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.

Heterologous expression of wheat WRKY transcription factor genes transcriptionally activated in hybrid necrosis strains alters abiotic and biotic stress tolerance in transgenic Arabidopsis

Hybrid necrosis and hybrid chlorosis are sometimes observed in interspecific hybrids between the tetraploid wheat cultivar Langdon and diploid wild wheat Aegilops tauschii. Many WRKY transcription factor genes are dramatically upregulated in necrosis and chlorosis wheat hybrids. Here, we isolated cDNA clones for four wheat WRKY transcription factor genes, TaWRKY49, TaWRKY92, TaWRKY112, and TaWRKY142, that were commonly upregulated in the hybrid necrosis and hybrid chlorosis and belonged to the same clade of the WRKY gene family. Expression patterns of the four TaWRKY genes in response to several stress conditions were similar in wheat seeding leaves. The four TaWRKY-GFP fusion proteins were targeted to the nucleus in onion epidermal cells. The TaWRKY gene expression levels were increased by high salt, dehydration, darkness, and blast fungus treatment in common wheat. Expression of either of the TaWRKY genes increased salinity and osmotic stress tolerance accompanied with overexpression of STZ/Zat10, and induced overexpression of the salicylic acid-signal pathway marker gene AtPR1 in transgenic Arabidopsis. TaWRKY142 expression also induced the jasmonic acid-pathway marker gene AtPDF1.2 and enhanced resistance against the fungal pathogen Colletotrichum higginsianum in transgenic Arabidopsis. These results suggest that the four TaWRKY genes act as integrated hubs of multiple stress signaling pathways in wheat and play important roles in autoimmune response-inducing hybrid necrosis and hybrid chlorosis.

Advances in biosynthesis, regulation, and metabolic engineering of plant specialized terpenoids

Plant specialized terpenoids are natural products that have no obvious role in growth and development, but play many important functional roles to improve the plant's overall fitness. Besides, plant specialized terpenoids have immense value to humans due to their applications in fragrance, flavor, cosmetic, and biofuel industries. Understanding the fundamental aspects involved in the biosynthesis and regulation of these high-value molecules in plants not only paves the path to enhance plant traits, but also facilitates homologous or heterologous engineering for overproduction of target molecules of importance. Recent developments in functional genomics and high-throughput analytical techniques have led to unraveling of several novel aspects involved in the biosynthesis and regulation of plant specialized terpenoids. The knowledge thus derived has been successfully utilized to produce target specialized terpenoids of plant origin in homologous or heterologous host systems by metabolic engineering and synthetic biology approaches. Here, we provide an overview and highlights on advances related to the biosynthetic steps, regulation, and metabolic engineering of plant specialized terpenoids.

Transgenesis as a Tool for the Efficient Production of Selected Secondary Metabolites from in Vitro Plant Cultures

The plant kingdom abounds in countless species with potential medical uses. Many of them contain valuable secondary metabolites belonging to different classes and demonstrating anticancer, anti-inflammatory, antioxidant, antimicrobial or antidiabetic properties. Many of these metabolites, e.g., paclitaxel, vinblastine, betulinic acid, chlorogenic acid or ferrulic acid, have potential applications in medicine. Additionally, these compounds have many therapeutic and health-promoting properties. The growing demand for these plant secondary metabolites forces the use of new green biotechnology tools to create new, more productive in vitro transgenic plant cultures. These procedures have yielded many promising results, and transgenic cultures have been found to be safe, efficient and cost-effective sources of valuable secondary metabolites for medicine and industry. This review focuses on the use of various in vitro plant culture systems for the production of secondary metabolites.

Transcriptome sequencing of Salvia miltiorrhiza after infection by its endophytic fungi and identification of genes related to tanshinone biosynthesis

Context: Salvia miltiorrhiza Bunge (Labiatae) is a traditional Chinese herb. Endophytic fungi, which are biotic elicitors, can induce accumulation of secondary metabolites in their host plants.Objective: To analyze the interaction mechanism between S. miltiorrhiza and endophytic fungi.Materials and methods: Endophytic fungi U104 producing tanshinone IIA were isolated from the healthy disease-free tissue of root of S. miltiorrhiza by conventional methods. The endophytic fungus U104 of S. miltiorrhiza was co-cultured with the sterile seedlings of S. miltiorrhiza for 20 d (temp:day/night = 26 °C/18 °C, photoperiod:12/12 h, illuminance:2000 Lx). Transcriptome sequencing of S. miltiorrhiza seedlings after 20 d of co-cultivation was performed using the Illumina platform.Results: A total of 3713 differentially expressed genes (DEGs) were obtained. These different expression genes, such as STPII, LTP2, MYB transcription factors, CNGC, CDPK, Rboh, CaM, MAP2K1/MEK1, WRKY33, SGT1/SGT and Hsp90/htpG, showed that host S. miltiorrhiza had biological defence response in the initial stage of interaction. Under the induction of endophytic fungi, 14 key enzyme genes were up-regulated in the tanshinone biosynthesis pathway: DXS, DXS2, DXR, HMGR3, AACT, MK, PMK, GGPPS2, GPPS, KSL, IDI, IPII, FDPS and CPS.Discussion and conclusions: A total of 14 key genes were obtained from the tanshinone component synthesis and metabolic pathways, providing a reasonable explanation for the accumulation of tanshinone components, an accumulation induced by endophytic fungi, in the host plants. The large amounts of data generated in this study provide a strong and powerful platform for future functional and molecular studies of interactions between host plants and their endophytic fungi.

Transcriptomic analysis reveals potential genes involved in tanshinone biosynthesis in Salvia miltiorrhiza

Tanshinones are important bioactive components in Salvia miltiorrhiza and mainly accumulate in the periderms of mature roots. Tanshinone biosynthesis is a complicated process, and little is known about the third stage of the pathway. To investigate potential genes that are responsible for tanshinone biosynthesis, we conducted transcriptome profiling analysis of two S. miltiorrhiza cultivars. Differential expression analysis provided 2,149 differentially expressed genes (DEGs) for further analysis. GO and KEGG analysis showed that the DEGs were mainly associated with the biosynthesis of secondary metabolites. Weighted gene coexpression network analysis (WGCNA) was further performed to identify a “cyan” module associated with tanshinone biosynthesis. In this module, 25 cytochromes P450 (CYPs), three 2-oxoglutarate-dependent dioxygenases (2OGDs), one short-chain alcohol dehydrogenases (SDRs) and eight transcription factors were found to be likely involved in tanshinone biosynthesis. Among these CYPs, 14 CYPs have been reported previously, and 11 CYPs were identified in this study. Expression analysis showed that four newly identified CYPs were upregulated upon application of MeJA, suggesting their possible roles in tanshinone biosynthesis. Overall, this study not only identified candidate genes involved in tanshinone biosynthesis but also provided a basis for characterization of genes involved in important active ingredients of other traditional Chinese medicinal plants.

Transcription Factor OpWRKY3 Is Involved in the Development and Biosynthesis of Camptothecin and Its Precursors in Ophiorrhiza pumila Hairy Roots

The plant Ophiorrhiza pumila produces camptothecin (CPT), a kind of terpene indole alkaloid (TIAs) that has been widely used in treatment of cancer. Tryptophan-arginine-lysine-tyrosine (WRKY) transcription factors have been reported to play important roles in plant metabolism and development. In this study, a novel WRKY transcription factor named OpWRKY3 was isolated from O. pumila, with full-length open reading frame (ORF) of 1128 bp, encoding 375 amino acids. Phylogenetic tree analysis revealed that OpWRKY3 shared the highest homology with VvWRKY30, and it is a significant feature belonging to group III. OpWRKY3 was responsive to various treatments, including gibberellin (GA₃), methyl jasmonate (MJ), acetylsalicylic acid (ASA), salicylic acid (SA), and abscisic acid (ABA). Besides, OpWRKY3 is expressed predominantly in stems. Subcellular localization analysis showed that OpWRKY3 localized in the nucleus. The biomass of OpWRKY3-SRDX transgenic hairy roots (S line) was visibly suppressed, while there were slight changes between overexpression of the OpWRKY3 line (OE line) and the control. In addition, the concentration and total production of camptothecin precursors including loganin and secologanin were significantly changed in both OE and S lines while total production of CPT was significantly changed in most transgenic lines. Thus, the present work revealed that OpWRKY3 may act as a regulator in the growth and development of O. pumila, and in production of camptothecin and its precursors.

Salvia miltiorrhiza in Treating Cardiovascular Diseases: A Review on Its Pharmacological and Clinical Applications

Bioactive chemical constitutes from the root of Salvia miltiorrhiza classified in two major groups, viz., liposoluble tanshinones and water-soluble phenolics. Tanshinone IIA is a major lipid-soluble compound having promising health benefits. The in vivo and in vitro studies showed that the tanshinone IIA and salvianolate have a wide range of cardiovascular and other pharmacological effects, including antioxidative, anti-inflammatory, endothelial protective, myocardial protective, anticoagulation, vasodilation, and anti-atherosclerosis, as well as significantly help to reduce proliferation and migration of vascular smooth muscle cells. In addition, some of the clinical studies reported that the S. miltiorrhiza preparations in combination with Western medicine were more effective for treatment of various cardiovascular diseases including angina pectoris, myocardial infarction, hypertension, hyperlipidemia, and pulmonary heart diseases. In this review, we demonstrated the potential applications of S. miltiorrhiza, including pharmacological effects of salvianolate, tanshinone IIA, and its water-soluble derivative, like sodium tanshinone IIA sulfonate. Moreover, we also provided details about the clinical applications of S. miltiorrhiza preparations in controlling the cardiovascular diseases.