DNA Methylation of Farnesyl Pyrophosphate Synthase, Squalene Synthase, and Squalene Epoxidase Gene Promoters and Effect on the Saponin Content of Eleutherococcus Senticosus

bZIP transcription factor responds to changes in light quality and affects saponins synthesis in Eleutherococcus senticosus

Light quality considerably influences plant secondary metabolism, yet the precise mechanism underlying its impact on Eleutherococcus senticosus remains elusive. Comprehensive metabolomic and transcriptomic analyses revealed that varying light quality alters the biosynthesis of triterpene saponins by modulating the expression of genes involved in the process in E. senticosus. Through correlation analysis of gene expression and saponin biosynthesis, we identified four light-responsive transcription factors, namely EsbZIP1, EsbZIP2, EsbZIP4, and EsbZIP5. EsbZIP transcription factors function in the nucleus, with light quality-dependent promoter activity. Except for EsbZIP2, the other EsbZIP transcription factors exhibit transcriptional self-activation. Furthermore, EsbZIP can bind to the promoter areas of genes that encode important enzymes (EsFPS, EsSS, and EsSE) involved in triterpene saponin biosynthesis, thereby regulating their expression. Overexpression of EsbZIP resultes in significant down-regulation of most downstream target genes，which leads to a decrease in saponin content. Overall, varying light quality enhances the content of triterpene saponins by suppressing the expression of EsbZIP. This study thus elucidates the molecular mechanism by which E. senticosus adjusts triterpene saponin levels in response to changes in light quality.

Linking soil nutrients, microbial community composition, and enzyme activities to saponin content of Paris polyphylla after addition of biochar and organic fertiliser

The application of organic fertilisers and biochar has become widespread in agroforestry ecosystems to enhance the yield and quality of crops and medicinal plants. However, their specific impact on both the yield and quality of Paris polyphylla (P. polyphylla), along with the underlying mechanisms, remains unclear. In this study, we investigated the distinct effects of organic fertiliser (at concentrations of 5% and 10%) and biochar application (at levels of 2% and 4%) on P. polyphylla saponin content. This content is intricately regulated by available soil nutrients, enzyme activities, and microbial community compositions and activities. Our results clearly demonstrated a significant increase in the saponin content, including total saponin, polyphyllin I (PPI), polyphyllin II (PPII), polyphyllin VI (PPVI), and polyphyllin VII (PPVII), in P. polyphylla following the application of both biochar and organic fertiliser. Moreover, in comparison to the control group, the addition of biochar and organic fertiliser led to a considerable rise in the activity of glycosyltransferase enzyme (GTS) and cycloartenol synthase (CAS) in P. polyphylla. Additionally, it increased soil available potassium (AK) and soil organic matter (SOM) concentration, along with the activity of urease, acid phosphatase, and catalase, although biochar amendment resulted in a decrease in nitrate nitrogen (NO3--N) concentration. Crucially, our findings revealed a positive correlation between total saponin content and the activity of CAS in P. polyphylla, soil AK, SOM concentration, and the activities of urease, acid phosphatase, and catalase. Conversely, there was a negative correlation with NO3--N content. Furthermore, the application of organic fertiliser and biochar significantly influenced microbial community structures and specific microbial taxa. Notably, total saponin content exhibited a positive relationship with the relative abundances of Dehalococcoidia, Saccharomycetes, and Agaricomycetes taxa while showing a negative correlation with the abundance of Verrucomicrobiae. In conclusion, the observed increase in saponin content can be attributed to the modulation of specific microbial taxa in soils, as well as alterations in soil nutrients and enzyme activities resulting from the application of biochar and organic fertiliser. This study identifies a potential mechanism for enhancing saponin content in the artificial cultivation of P. polyphylla.

Identification of Eleutherococcus senticosus NAC transcription factors and their mechanisms in mediating DNA methylation of EsFPS, EsSS, and EsSE promoters to regulate saponin synthesis

BACKGROUND

The formation of pharmacologically active components in medicinal plants is significantly impacted by DNA methylation. However, the exact mechanisms through which DNA methylation regulates secondary metabolism remain incompletely understood. Research in model species has demonstrated that DNA methylation at the transcription factor binding site within functional gene promoters can impact the binding of transcription factors to target DNA, subsequently influencing gene expression. These findings suggest that the interaction between transcription factors and target DNA could be a significant mechanism through which DNA methylation regulates secondary metabolism in medicinal plants.

RESULTS

This research conducted a comprehensive analysis of the NAC family in E. senticosus, encompassing genome-wide characterization and functional analysis. A total of 117 EsNAC genes were identified and phylogenetically divided into 15 subfamilies. Tandem duplications and chromosome segment duplications were found to be the primary replication modes of these genes. Motif 2 was identified as the core conserved motif of the genes, and the cis-acting elements, gene structures, and expression patterns of each EsNAC gene were different. EsJUB1, EsNAC047, EsNAC098, and EsNAC005 were significantly associated with the DNA methylation ratio in E. senticosus. These four genes were located in the nucleus or cytoplasm and exhibited transcriptional self-activation activity. DNA methylation in EsFPS, EsSS, and EsSE promoters significantly reduced their activity. The methyl groups added to cytosine directly hindered the binding of the promoters to EsJUB1, EsNAC047, EsNAC098, and EsNAC005 and altered the expression of EsFPS, EsSS, and EsSE genes, eventually leading to changes in saponin synthesis in E. senticosus.

CONCLUSIONS

NAC transcription factors that are hindered from binding by methylated DNA are found in E. senticosus. The incapacity of these NACs to bind to the promoter of the methylated saponin synthase gene leads to subsequent alterations in gene expression and saponin synthesis. This research is the initial evidence showcasing the involvement of EsNAC in governing the impact of DNA methylation on saponin production in E. senticosus.

DNA methylation regulates the secondary metabolism of saponins to improve the adaptability of Eleutherococcus senticosus during drought stress

Plant growth and development can be significantly impacted by drought stress. Plants will adjust the synthesis and accumulation of secondary metabolites to improve survival in times of water constraint. Simultaneously, drought stress can lead to modifications in the DNA methylation status of plants, and these modifications can directly impact gene expression and product synthesis by changing the DNA methylation status of functional genes involved in secondary metabolite synthesis. However, further research is needed to fully understand the extent to which DNA methylation modifies the content of secondary metabolites to mediate plants' responses to drought stress, as well as the underlying mechanisms involved. Our study found that in Eleutherococcus senticosus (E. senticosus), moderate water deprivation significantly decreased DNA methylation levels throughout the genome and at the promoters of EsFPS, EsSS, and EsSE. Transcription factors like EsMYB-r1, previously inhibited by DNA methylation, can re-bind to the EsFPS promotor region following DNA demethylation. This process promotes gene expression and, ultimately, saponin synthesis and accumulation. The increased saponin levels in E. senticosus acted as antioxidants, enhancing the plant's adaptability to drought stress.

Progress and Prospects of Natural Glycoside Sweetener Biosynthesis: A Review

To achieve an adequate sense of sweetness with a healthy low-sugar diet, it is necessary to explore and produce sugar alternatives. Recently, glycoside sweeteners and their biosynthetic approaches have attracted the attention of researchers. In this review, we first outlined the synthetic pathways of glycoside sweeteners, including the key enzymes and rate-limiting steps. Next, we reviewed the progress in engineered microorganisms producing glycoside sweeteners, including de novo synthesis, whole-cell catalysis synthesis, and in vitro synthesis. The applications of metabolic engineering strategies, such as cofactor engineering and enzyme modification, in the optimization of glycoside sweetener biosynthesis were summarized. Finally, the prospects of combining enzyme engineering and machine learning strategies to enhance the production of glycoside sweeteners were discussed. This review provides a perspective on synthesizing glycoside sweeteners in microbial cells, theoretically guiding the bioproduction of glycoside sweeteners.

Plant Hormone and Fatty Acid Screening of Nicotiana tabacum and Lilium longiflorum Stigma Exudates

Pollen germination in vivo on wet stigmas is assisted by the receptive fluid-stigma exudate. Its exact composition is still unknown because only some components have been studied. For the first time, hormonal screening was carried out, and the fatty acid (FA) composition of lipid-rich (Nicotiana tabacum) and sugar-rich (Lilium longiflorum) exudates was studied. Screening of exudate for the presence of plant hormones using HPLC-MS revealed abscisic acid (ABA) in tobacco stigma exudate at the two stages of development, at pre-maturity and in mature stigmas awaiting pollination, increasing at the fertile stage. To assess physiological significance of ABA on stigma, we tested the effect of this hormone in vitro. ABA concentration found in the exudate strongly stimulated the germination of tobacco pollen, a lower concentration had a weaker effect, increasing the concentration did not increase the effect. GC-MS analysis showed that both types of exudate are characterized by a predominance of saturated FAs. The lipids of tobacco stigma exudate contain significantly more myristic, oleic, and linoleic acids, resulting in a higher unsaturation index relative to lily stigma exudate lipids. The latter, in turn, contain more 14-hexadecenoic and arachidic acids. Both exudates were found to contain significant amounts of squalene. The possible involvement of saturated FAs, ABA, and squalene in various exudate functions, as well as their potential relationship on the stigma, is discussed.

Genome-wide identification of MBD gene family members in Eleutherococcus senticosus with their expression motifs under drought stress and DNA demethylation

BACKGROUND

Methyl-binding domain (MBD) is a class of methyl-CpG-binding domain proteins that affects the regulation of gene expression through epigenetic modifications. MBD genes are not only inseparable from DNA methylation but have also been identified and validated in various plants. Although MBD is involved in a group of physiological processes and stress regulation in these plants, MBD genes in Eleutherococcus senticosus remain largely unknown.

RESULTS

Twenty EsMBD genes were identified in E. senticosus. Among the 24 chromosomes of E. senticosus, EsMBD genes were unevenly distributed on 12 chromosomes, and only one tandem repeat gene existed. Collinearity analysis showed that the fragment duplication was the main motif for EsMBD gene expansion. As the species of Araliaceae evolved, MBD genes also evolved and gradually exhibited different functional differentiation. Furthermore, cis-acting element analysis showed that there were numerous cis-acting elements in the EsMBD promoter region, among which light response elements and anaerobic induction elements were dominant. The expression motif analysis revealed that 60% of the EsMBDs were up-regulated in the 30% water content group.

CONCLUSIONS

By comparing the transcriptome data of different saponin contents of E. senticosus and integrating them with the outcomes of molecular docking analysis, we hypothesized that EsMBD2 and EsMBD5 jointly affect the secondary metabolic processes of E. senticosus saponins by binding to methylated CpG under conditions of drought stress. The results of this study laid the foundation for subsequent research on the E. senticosus and MBD genes.

Metabolome and transcriptome analysis of eleutheroside B biosynthesis pathway in Eleutherococcus senticosus

Eleutheroside B (syringin) is a medicinal active ingredient extracted from Eleutherococcus senticosus (Ruper. et Maxim.) Maxim with high clinical application value. However, its synthesis pathway remains unknown. Here, we analyzed the eleutheroside B biosynthesis pathway in E. senticosus. Consequently, metabolomic and transcriptomic analyses identified 461 differentially expressed genes (DEGs) and 425 metabolites. Further, we identified 7 DEGs and 67 metabolites involved in the eleutheroside B biosynthetic pathway in the eleutheroside B high and low plants. The correlation between the gene and metabolites was explored using the pearson correlation coefficient (PCC) analysis. Caffeoyl-CoA O-methyltransferase, caffeic acid-O-methyltransferase, β-amyrin synthase (β-AS) genes, NAC5, and HB5 transcription factors were identified as candidate genes and transcription factors related to the eleutheroside B synthesis. Eleutheroside B content was the highest at the young stage of the leaves both in the high and low eleutheroside B plants. Quantitative real-time polymerase chain reaction revealed that phenylalanine ammonia-lyase1, cinnamate 4-hydroxylase, β-AS, and leucoanthocyanidin reductase gene had higher expression levels at the young stage of the leaves in the low eleutheroside B plants but lower expression levels in the high eleutheroside B plants. In the present study, we complemented the eleutheroside B biosynthetic pathway by analyzing the expression levels of relevant genes and metabolite accumulation patterns.