Characterization of MYB35 regulated methyl jasmonate and wound responsive Geraniol 10-hydroxylase-1 gene from Bacopa monnieri

Engineering Bacopa monnieri for improved bacoside content and its neurological evaluation

Bacosides are triterpenoidal saponins with numerous pharmacological benefits. One of the significant drawbacks is the low availability of these bacosides. The bacoside pathway is not well elucidated, and there is no prior report of a metabolic engineering approach in this plant. In this study, we have over-expressed the active isoform of Bacopa monnieri squalene synthase (BmSQS1-OE) and silenced the B. monnieri G10H (BmG10H-1-KD), the competitive metabolic pathway, to divert the flux towards triterpene biosynthesis. Absolute quantification of bacosides in these BmSQS1(OE)-BmG10H1(KD) lines has identified improved content of bacoside A3, bacopaside II, and bacoside A. Moreover, the engineered plant extract was also found to have better efficacy on locomotor activity, neuromuscular coordination, and social interaction in a 6-hydroxydopamine (6-OHDA)-induced rat model of Parkinson's disease (PD). Immunohistochemistry of the brain tissues indicates that an extract of enhanced bacoside contents reduces 6-OHDA-induced dopaminergic depletion, implying a potential utility in neurological disorders. KEY POINTS: • The engineered Bacopa monnieri extract has improved amounts of various bacoside. • The engineered Bacopa extract has shown enhanced effectiveness in a 6-hydroxydopamine (6-OHDA)-induced rat model of Parkinson's disease (PD).

Cloning and functional verification of Geraniol-10-Hydroxylase gene in Lonicera japonica

Background

Geraniol 10-hydroxylase (G10H) is a cytochrome P450 monooxygenase involved in regulation, which is involved in the biosynthesis of monoterpene. However, G10H is not characterized at the enzymatic mechanism and regulatory function in Lonicera japonica.

Methods and Results

A gene related to the biosynthesis of monoterpenoid, geraniol 10-hydroxylase, has been cloned from the medicinal plant Lonicera japonica. The gene, LjG10H, encodes a peptide of 498 amino acids with a predicted molecular weight of 54.45 kDa. LjG10H shares a homology of 72.93-83.90% with G10H from other plants. Phylogenetic analysis suggests that the protein encoded by this gene belongs to the cytochrome P450 monooxygenase family. Tissue-specific expression analysis revealed that LjG10H is most highly expressed in flowers. Through heterologous expression in E. coli, the LjG10H protein was purified and its catalytic activity was studied. The results show that the enzyme can catalyze the hydroxylation of geraniol to 10-hydroxygeraniol. Additionally, analysis of Lonicera japonica seedlings with silenced LjG10H revealed a reduction in monoterpenoid content.

Conclusions

This study demonstrates that LjG10H plays an important role in the biosynthetic pathway of iridoids. This is the first article that ascribes G10H to be associated with the biosynthetic pathway of iridoid. This study provides a theoretical basis for the functional mechanism of LjG10H in regulating iridoid synthesis and provides a valuable resource for molecular breeding studies.

Transcriptomics and metabolomics analyses reveal pollen abortion mechanism in alfalfa early stage male sterile lines

Alfalfa (Medicago sativa L.), a prominent perennial forage in the legume family, is widely cultivated across Europe and America. Given its substantial economic value for livestock, breeding efforts have focused on developing high-yield and high-quality varieties since the discovery of CMS lines. However, progress is restricted by the limitations of existing CMS lines, necessitating the development of new lines and study of the molecular mechanisms underlying pollen abortion. This study investigates early-stage anther development in cytoplasmic male sterile (CMS) alfalfa lines (MSJN1A) in relation to the isotypic maintainer line (MSJN1B). Histological analyses revealed abnormal degradation of tapetal cells post-meiosis in the CMS line. Notably, during the early mononuclear stage, the central vacuoles in the microspores were absent, leading to evident pollen abortion. These findings suggest that pollen abortion in the CMS line is associated with the delayed disintegration of the tapetum and structural anomalies in microspore vacuoles. Non-targeted metabolome sequencing revealed 401 and 405 metabolites at late tetrad and early mononuclear stages of alfalfa, respectively. Among these, 39 metabolites were consistently upregulated, whereas 85 metabolites were downregulated. Differential analysis revealed 45 and 37 unique metabolites at each respective stage. These metabolites were primarily featured in pathways related to energy, phenylpropane, sucrose and starch, and fatty acid metabolism. Integrated analysis demonstrated that differentially expressed genes and differential metabolites were co-enriched in these pathways. Additionally, quantitative real-time PCR and physiological index analysis confirmed downregulation of key genes involved in anther development, illustrating that changes in upstream gene regulation could significantly impact downstream metabolite levels, ultimately influencing pollen fertility. Pollen abortion is related to abnormal phenylpropane metabolism, fatty acid metabolism and starch and sucrose pathway, which provides reference for further research on the causes of pollen abortion of alfalfa.

Methyl jasmonate inducible UGT79A18 is a novel glycosyltransferase involved in the bacoside biosynthetic pathway in Bacopa monnieri

Bacosides are dammarane-type triterpenoidal saponins in Bacopa monnieri and have various pharmacological applications. All the bacosides are diversified from two isomers, i.e., jujubogenin and pseudojujubogenin. The biosynthetic pathway of bacoside is not well elucidated. In the present study, we characterized a UDP-glycosyltransferase, UGT79A18, involved in the glycosylation of pseudojujubogenin. UGT79A18 shows higher expression in response to 5 h of wounding, and 3 h of MeJA treatment. The recombinant UGT79A18 shows in vitro activity against a wide range of flavonoids and triterpenes and has a substrate preference for protopanaxadiol, a dammarane-type triterpene. Secondary metabolite analysis of overexpression and knockdown lines of UGT79A18 in B. monnieri identify bacopasaponin D, bacopaside II, bacopaside N2 and pseudojujubogenin glucosyl rhamnoside as the major bacosides that were differentially accumulated. In the overexpression lines of UGT79A18, we found 1.7-fold enhanced bacopaside II, 8-fold enhanced bacopasaponin D, 3-fold enhanced pseudojujubogenin glucosyl rhamnoside, and 1.6-fold enhanced bacopaside N2 content in comparison with vector control plant, whereas in the knockdown lines of UGT79A18, we found 1.4-fold reduction in bacopaside II content, 3-fold reduction in the bacopasaponin D content, 2-fold reduction in the pseudojujubogenin glucosyl rhamnoside content, and 1.5-fold reduction in bacopaside N2 content in comparison with vector control. These results suggest that UGT79A18 is a significant UDP glycosyltransferase involved in glycosylating pseudojujubogenin and enhancing the pseudojujubogenin-derived bacosides.

Genome-wide identification and expression analysis of MYB gene family in Cajanus cajan and CcMYB107 improves plant drought tolerance

MYB transcription factor (TF) is one of the largest superfamilies that play a vital role in multiple plant biological processes. However, the MYB family has not been comprehensively identified and functionally verified in Cajanus cajan, which is the sixth most important legume crop. Here, 170 CcR2R3-MYBs were identified and divided into 43 functional subgroups. Segmental and tandem duplications and alternative splicing events were found and promoted the expansion of the CcR2R3-MYB gene family. Functional prediction results showed that CcR2R3-MYBs were mainly involved in secondary metabolism, cell fate and identity, developmental processes, and responses to abiotic stress. Cis-acting element analysis of promoters revealed that stress response elements were widespread in the above four functional branches, further suggesting CcR2R3-MYBs were extensively involved in abiotic stress response. The transcriptome data and qRT-PCR results indicated that most of the CcR2R3-MYB genes responded to various stresses, of which the expression of CcMYB107 was significantly induced by drought stress. Overexpression of CcMYB107 enhanced antioxidant enzyme activity and increased proline and lignin accumulation, thus improving the drought resistance of C. cajan. Furthermore, Overexpression of CcMYB107 up-regulated the expression of stress-related genes and lignin biosynthesis genes after drought stress. Our findings established a strong foundation for the investigation of biological function of CcR2R3-MYB TFs in C. cajan.

Development of a MAGIC population and high-resolution quantitative trait mapping for nicotine content in tobacco

Multiparent Advanced Generation Inter-Cross (MAGIC) population is an ideal genetic and breeding material for quantitative trait locus (QTL) mapping and molecular breeding. In this study, a MAGIC population derived from eight tobacco parents was developed. Eight parents and 560 homozygous lines were genotyped by a 430K single-nucleotide polymorphism (SNP) chip assay and phenotyped for nicotine content under different conditions. Four QTLs associated with nicotine content were detected by genome-wide association mapping (GWAS), and one major QTL, named qNIC7-1, was mapped repeatedly under different conditions. Furthermore, by combining forward mapping, bioinformatics analysis and gene editing, we identified an ethylene response factor (ERF) transcription factor as a candidate gene underlying the major QTL qNIC7-1 for nicotine content in tobacco. A presence/absence variation (PAV) at qNIC7-1 confers changes in nicotine content. Overall, the large size of this MAGIC population, diverse genetic composition, balanced parental contributions and high levels of recombination all contribute to its value as a genetic and breeding resource. The application of the tobacco MAGIC population for QTL mapping and detecting rare allelic variation was demonstrated using nicotine content as a proof of principle.

MYB transcription factors and their role in Medicinal plants

Transcription factors are multi-domain proteins that regulate gene expression in eukaryotic organisms. They are one of the largest families of proteins, which are structurally and functionally diverse. While there are transcription factors that are plant-specific, such as AP2/ERF, B3, NAC, SBP and WRKY, some transcription factors are present in both plants as well as other eukaryotic organisms. MYB transcription factors are widely distributed among all eukaryotes. In plants, the MYB transcription factors are involved in the regulation of numerous functions such as gene regulation in different metabolic pathways especially secondary metabolic pathways, regulation of different signalling pathways of plant hormones, regulation of genes involved in various developmental and morphological processes etc. Out of the thousands of MYB TFs that have been studied in plants, the majority of them have been studied in the model plants like Arabidopsis thaliana, Oryza sativa etc. The study of MYBs in other plants, especially medicinal plants, has been comparatively limited. But the increasing demand for medicinal plants for the production of biopharmaceuticals and important bioactive compounds has also increased the need to explore more number of these multifaceted transcription factors which play a significant role in the regulation of secondary metabolic pathways. These studies will ultimately contribute to medicinal plants' research and increased production of secondary metabolites, either through transgenic plants or through synthetic biology approaches. This review compiles studies on MYB transcription factors that are involved in the regulation of diverse functions in medicinal plants.

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.

Biotechnological production of bacosides from cell and organ cultures of Bacopa monnieri

Bacopa monnieri (L.) Wettst. (BM), also known as 'Brahmi' or 'Water Hyssop', has been utilized as a brain tonic, memory enhancer, sensory organ revitalizer, cardiotonic, anti-anxiety, antidepressant and anticonvulsant agent in the Indian system of medicine Ayurveda for centuries. BM is beneficial in the treatment of Parkinson's disease, Alzheimer's disease, epileptic seizures and schizophrenia in recent pharmacological research. Dammarane-type triterpenoid saponins containing jujubogenin and pseudojujubogenin as aglycones, also known as bacosides, are the principal chemical ingredients identified and described from BM. Bacosides have been shown to have anti-ageing, anticancer, anticonvulsant, antidepressant, anti-emetic, anti-inflammatory and antibacterial properties in a variety of pre-clinical and clinical studies. The pharmaceutical industry's raw material comes from wild sources; nevertheless, the concentration of bacosides varies in different regions of the plants, as well as seasonal and genotypic variation. Cell and tissue cultures are appealing alternatives for the long-term manufacture of bioactive chemicals, and attempts to produce bacosides using in vitro cultures have been made. This review discusses the biotechnological approaches used to produce bacosides, as well as the limitations and future potential. KEY POINTS: • Bacosides extracted from Bacopa monnieri are important pharmaceutical compounds. • The current review provides insight into biotechnological interventions for the production of bacosides using in vitro cultures. • Highlights the prospects improvement of bacoside production through metabolic engineering.

Role of female-predominant MYB39-bHLH13 complex in sexually dimorphic accumulation of taxol in Taxus media

Taxus trees are major natural sources for the extraction of taxol, an anti-cancer agent used worldwide. Taxus media is a dioecious woody tree with high taxol yield. However, the sexually dimorphic accumulation of taxoids in T. media is largely unknown. Our study revealed high accumulation of taxoids in female T. media trees using a UPLC-MS/MS method. Thereafter, many differential metabolites and genes between female and male T. media trees were identified using metabolomic and transcriptomic analyses, respectively. Most of the taxol-related genes were predominantly expressed in female trees. A female-specific R2R3-MYB transcription factor gene, TmMYB39, was identified. Furthermore, bimolecular fluorescence complementation and yeast two-hybrid assays suggested the potential interaction between TmMYB39 and TmbHLH13. Several taxol biosynthesis-related promoter sequences were isolated and used for the screening of MYB recognition elements. The electrophoretic mobility shift assay indicated that TmMYB39 could bind to the promoters of the GGPPS, T10OH, T13OH, and TBT genes. Interaction between TmMYB39 and TmbHLH13 transactivated the expression of the GGPPS and T10OH genes. TmMYB39 might function in the transcriptional regulation of taxol biosynthesis through an MYB-bHLH module. Our results give a potential explanation for the sexually dimorphic biosynthesis of taxol in T. media.