PnMYB4 negatively modulates saponin biosynthesis in Panax notoginseng through interplay with PnMYB1

Transcriptome-based analysis of key functional genes in the triterpenoid saponin synthesis pathway of Platycodon grandiflorum

BACKGROUND

Platycodon grandiflorum (P. grandiflorum) is a commonly used medicinal plant in China. Transcriptome sequencing studies of different tissues of P. grandiflorum have been widely conducted. However, studies on transcriptome sequencing and expression patterns of key genes in the saponin synthesis pathway of Tongcheng P. grandiflorum, a high-quality medicinal resource of different years, are relatively limited.

RESULTS

This study involved transcriptome sequencing and bioinformatics analysis of the roots from annual, biennial, and triennial P. grandiflorum in the Tongcheng area. After data filtering and assembly, we obtained 111.44 Gb of clean base data, including 742,880616 clean reads. We identified 5,156 differential expression unigenes between at least two sample groups, with differences noted among annual, biennial, and triennial P. grandiflorum plants. GO enrichment analysis annotated 3509, 1819, and 1393 DEGs in comparison TC1vsTC2, TC1vsTC3, and TC2vsTC3, respectively. Furthermore, KEGG enrichment analysis identified 16 genes encoding key enzymes in the terpene skeleton biosynthesis, sesquiterpene and triterpene biosynthesis pathways, including SE, AACT, FPPS, DXR, HMGR, HMGS, and DXS. The results of qRT-PCR experiments showed that most of the genes were most highly expressed in annual P. grandiflorum.

CONCLUSIONS

The present study provided transcriptomic data from the roots of Tongcheng P. grandiflorum of different years, which provides critical bioinformatics data on the growth and development of P. grandiflorum, laying a foundation for further research on saponins and identifying key enzymes involved in this process across different growth stages.

Comparative transcriptomic and metabolomic analyses reveal key regulatory gene for methyl jasmonate-induced steroidal saponins synthesis in Dioscorea composita

Dioscorea composita (D. composita) is a perennial herb with abundant steroidal saponins that have gained worldwide attention for their remarkable efficacy in cardiovascular diseases. However, few studies have been worked on the regulatory network of steroidal saponins biosynthesis under phytohormone induced. In this study, we combined the transcriptome and metabolome analysis to reveal the variation of diosgenin and steroidal saponins in transcriptional and metabolism levels under methyl-jasmonate (MeJA) treatment. Although the application of MeJA indeed significantly increased the accumulation of diosgenin of D. composita, different types of steroidal saponins exhibited different accumulation patterns. Consistently, the expression levels of UDP-glycosyltransferases and Cytochrome P450 monooxygenases genes that highly related to the accumulation of steroidal saponins were either up- or down-regulated. Correlation analyses of transcription factors (TFs)-steroidal saponins and structural genes-TFs were further to identified the TFs potentially involved in the regulation of steroidal saponins biosynthesis. Silencing of DcWRKY11 in Dioscorea composita decreases the accumulation of steroidal saponins by regulating the expression steroidal saponins synthesis genes, suggesting that DcWRKY11 is a positive regulator in the regulation of steroidal saponins biosynthesis. Our findings take a deeper understanding of the regulatory network of MeJA-mediated steroidal saponins biosynthesis in D. composita.

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

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

Soybean steroids improve crop abiotic stress tolerance and increase yield

Sterols have long been associated with diverse fields, such as cancer treatment, drug development, and plant growth; however, their underlying mechanisms and functions remain enigmatic. Here, we unveil a critical role played by a GmNF-YC9-mediated CCAAT-box transcription complex in modulating the steroid metabolism pathway within soybeans. Specifically, this complex directly activates squalene monooxygenase (GmSQE1), which is a rate-limiting enzyme in steroid synthesis. Our findings demonstrate that overexpression of either GmNF-YC9 or GmSQE1 significantly enhances soybean stress tolerance, while the inhibition of SQE weakens this tolerance. Field experiments conducted over two seasons further reveal increased yields per plant in both GmNF-YC9 and GmSQE1 overexpressing plants under drought stress conditions. This enhanced stress tolerance is attributed to the reduction of abiotic stress-induced cell oxidative damage. Transcriptome and metabolome analyses shed light on the upregulation of multiple sterol compounds, including fucosterol and soyasaponin II, in GmNF-YC9 and GmSQE1 overexpressing soybean plants under stress conditions. Intriguingly, the application of soybean steroids, including fucosterol and soyasaponin II, significantly improves drought tolerance in soybean, wheat, foxtail millet, and maize. These findings underscore the pivotal role of soybean steroids in countering oxidative stress in plants and offer a new research strategy for enhancing crop stress tolerance and quality from gene regulation to chemical intervention.

Panax notoginseng: panoramagram of phytochemical and pharmacological properties, biosynthesis, and regulation and production of ginsenosides

Panax notoginseng is a famous perennial herb widely used as material for medicine and health-care food. Due to its various therapeutic effects, research work on P. notoginseng has rapidly increased in recent years, urging a comprehensive review of research progress on this important medicinal plant. Here, we summarize the latest studies on the representative bioactive constituents of P. notoginseng and their multiple pharmacological effects, like cardiovascular protection, anti-tumor, and immunomodulatory activities. More importantly, we emphasize the biosynthesis and regulation of ginsenosides, which are the main bioactive ingredients of P. notoginseng. Key enzymes and transcription factors (TFs) involved in the biosynthesis of ginsenosides are reviewed, including diverse CYP450s, UGTs, bHLH, and ERF TFs. We also construct a transcriptional regulatory network based on multi-omics data and predicted candidate TFs mediating the biosynthesis of ginsenosides. Finally, the current three major biotechnological approaches for ginsenoside production are highlighted. This review covers advances in the past decades, providing insights into quality evaluation and perspectives for the rational utilization and development of P. notoginseng resources. Modern omics technologies facilitate the exploration of the molecular mechanisms of ginsenoside biosynthesis, which is crucial to the breeding of novel P. notoginseng varieties. The identification of functional enzymes for biosynthesizing ginsenosides will lead to the formulation of potential strategies for the efficient and large-scale production of specific ginsenosides.

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.

PnNAC2 promotes the biosynthesis of Panax notoginseng saponins and induces early flowering

KEY MESSAGE

PnNAC2 positively regulates saponin biosynthesis by binding the promoters of key biosynthetic genes, including PnSS, PnSE, and PnDS. PnNAC2 accelerates flowering through directly associating with the promoters of FT genes. NAC transcription factors play an important regulatory role in both terpenoid biosynthesis and flowering. Saponins with multiple pharmacological activities are recognized as the major active components of Panax notoginseng. The P. notoginseng flower is crucial for growth and used for medicinal and food purposes. However, the precise function of the P. notoginseng NAC transcription factor in the regulation of saponin biosynthesis and flowering remains largely unknown. Here, we conducted a comprehensive characterization of a specific NAC transcription factor, designated as PnNAC2, from P. notoginseng. PnNAC2 was identified as a nuclear-localized protein with transcription activator activity. The expression profile of PnNAC2 across various tissues mirrored the accumulation pattern of total saponins. Knockdown experiments of PnNAC2 in P. notoginseng calli revealed a significant reduction in saponin content and the expression level of pivotal saponin biosynthetic genes, including PnSS, PnSE, and PnDS. Subsequently, Y1H assays, dual-LUC assays, and electrophoretic mobility shift assays (EMSAs) demonstrated that PnNAC2 exhibits binding affinity to the promoters of PnSS, PnSE and PnDS, thereby activating their transcription. Additionally, an overexpression assay of PnNAC2 in Arabidopsis thaliana witnessed the acceleration of flowering and the induction of the FLOWERING LOCUS T (FT) gene expression. Furthermore, PnNAC2 demonstrated the ability to bind to the promoters of AtFT and PnFT genes, further activating their transcription. In summary, these results revealed that PnNAC2 acts as a multifunctional regulator, intricately involved in the modulation of triterpenoid saponin biosynthesis and flowering processes.