Transcriptome analysis of Hevea brasiliensis in response to exogenous methyl jasmonate provides novel insights into regulation of jasmonate-elicited rubber biosynthesis

Integrated multi-omic analysis reveals the cytokinin and sucrose metabolism-mediated regulation of flavone glycoside biosynthesis by MeJA exposure in Ficus pandurata Hance

Ficus pandurata Hance (FPH) holds a rich history as a traditional Chinese botanical remedy, utilized both as a culinary condiment and a medicinal intervention for diverse ailments. This study focuses on enhancing FPH's therapeutic potential by subjecting it to exogenous methyl jasmonate (MeJA) treatment, a strategy aimed at elevating the levels of active constituents to align with clinical and commercial requirements. Employing metabolomics, the impact of MeJA treatment on the lipid and flavonoid profiles of FPH leaves was investigated, revealing a marked increase in flavone glycosides, a subset of flavonoids. Investigation into the regulatory mechanism governing flavone glycoside biosynthesis uncovered elevated expression of structural genes associated with flavonoid production in response to MeJA exposure. Global endogenous hormone analysis pinpointed the selective activation of JA and cytokinin biosynthesis following MeJA treatment. Through a comprehensive integration of transcriptomic and metabolomic data, the cooperative stimulation of glucosyltransferase activity, alongside the JA and cytokinin signaling pathways, orchestrated by MeJA were explored. Furthermore, genes linked to sucrose metabolism exhibited heightened expression, concomitant with a noteworthy surge in antioxidant activity subsequent to MeJA treatment. These findings validate the augmentation of FPH leaf antioxidant capacity through MeJA intervention, while also offering profound insights into the regulatory role of MeJA in flavone glycoside biosynthesis, mediated by the interplay between cytokinin and sucrose metabolism pathways.

An Investigation of the JAZ Family and the CwMYC2-like Protein to Reveal Their Regulation Roles in the MeJA-Induced Biosynthesis of β-Elemene in Curcuma wenyujin

β-Elemene (C15H24), a sesquiterpenoid compound isolated from the volatile oil of Curcuma wenyujin, has been proven to be effective for multiple cancers and is widely used in clinical treatment. Unfortunately, the β-elemene content in C. wenyujin is very low, which cannot meet market demands. Our previous research showed that methyl jasmonate (MeJA) induced the accumulation of β-elemene in C. wenyujin. However, the regulatory mechanism is unclear. In this study, 20 jasmonate ZIM-domain (JAZ) proteins in C. wenyujin were identified, which are the core regulatory factors of the JA signaling pathway. Then, the conservative domains, motifs composition, and evolutionary relationships of CwJAZs were analyzed comprehensively and systematically. The interaction analysis indicated that CwJAZs can form homodimers or heterodimers. Fifteen out of twenty CwJAZs were significantly induced via MeJA treatment. As the master switch of the JA signaling pathway, the CwMYC2-like protein has also been identified and demonstrated to interact with CwJAZ2/3/4/5/7/15/17/20. Further research found that the overexpression of the CwMYC2-like gene increased the accumulation of β-elemene in C. wenyujin leaves. Simultaneously, the expressions of HMGR, HMGS, DXS, DXR, MCT, HDS, HDR, and FPPS related to β-elemene biosynthesis were also up-regulated by the CwMYC2-like protein. These results indicate that CwJAZs and the CwMYC2-like protein respond to the JA signal to regulate the biosynthesis of β-elemene in C. wenyujin.

MeJA-mediated enhancement of salt-tolerance of Populus wutunensis by 5-aminolevulinic acid

BACKGROUND

5-Aminolevulinic acid (ALA) is a natural and environmentally benign multifunctional plant growth regulator involved in the regulation of plant tolerance to various environmental stresses. This research aimed to explore the molecular mechanisms of salt tolerance in Populus wutunensis induced by exogenous ALA using physiological and transcriptomic analyses.

RESULTS

Physiological results showed that 50 mg·L^- 1 ALA-treatment significantly reduced the malondialdehyde (MDA) content and the relative electrical conductivity (REC) and enhanced antioxidant activities of enzymes such as SOD, POD and CAT in salt-stressed P. wutunensis seedlings. Transcriptome analysis identified ALA-induced differentially expressed genes (DEGs) associating with increased salt-tolerance in P. wutunensis. GO and KEGG enrichment analyses showed that ALA activated the jasmonic acid signaling and significantly enhanced the protein processing in endoplasmic reticulum and the flavonoid biosynthesis pathways. Results of the hormone-quantification by LC-MS/MS-based assays showed that ALA could increase the accumulation of methyl jasmonate (MeJA) in salt-stressed P. wutunensis. Induced contents of soluble proteins and flavonoids by exogenous ALA in salt-treated seedlings were also correlated with the MeJA content.

CONCLUSION

5-aminolevulinic acid improved the protein-folding efficiency in the endoplasmic reticulum and the flavonoid-accumulation through the MeJA-activated jasmonic acid signaling, thereby increased salt-tolerance in P. wutunensis.

Transcriptome analysis of Taraxacum kok-saghyz reveals the role of exogenous methyl jasmonate in regulating rubber biosynthesis and drought tolerance

Taraxacum kok-saghyz has been identified as one of the most promising alternative rubber crops, with laticifer cells that produce high-quality rubber. To uncover the underlying molecular mechanisms regulating natural rubber biosynthesis under MeJA induction, a reference transcriptome was constructed from nine samples of T. kok-saghyz. MeJA treatment was applied for 0 h (control), 6 h, and 24 h. A total of 7452 differentially expressed genes (DEGs) were identified in response to MeJA stress, relative to the control. Functional enrichment showed that these DEGs were primarily related to hormone signaling, defensive responses, and secondary metabolism. Combined analysis of the DEGs induced by MeJA and high-expression genes in laticifer cells further identified seven DEGs related to natural rubber biosynthesis that were upregulated in latex tissue, suggesting that these candidate genes could prove valuable in studying the mechanism of MeJA-mediated natural rubber biosynthesis. In addition, 415 MeJA-responsive DEGs were from several transcription factor families associated with drought resistance. This study helps to elucidate the mechanism of natural rubber biosynthesis in T. kok-saghyz in response to MeJA stress and identifies key candidate MeJA-induced DEGs in laticifer tissue, as well as a candidate drought-response target gene, whose knowledge will promote the breeding of T. kok-saghyz in the aspect of rubber yields and quality, and drought tolerance.

Functional Characterization of TkSRPP Promoter in Response to Hormones and Wounding Stress in Transgenic Tobacco

Taraxacum kok-saghyz is a model species for studying natural rubber biosynthesis because its root can produce high-quality rubber. Small rubber particle protein (SRPP), a stress-related gene to multiple stress responses, involves in natural rubber biosynthesis. To investigate the transcriptional regulation of the TkSRPP promoter, the full-length promoter PR0 (2188 bp) and its four deletion derivatives, PR1 (1592 bp), PR2 (1274 bp), PR3 (934 bp), and PR4 (450 bp), were fused to β-glucuronidase (GUS) reporter gene and transformed into tobacco. The GUS tissue staining showed that the five promoters distinctly regulated GUS expression utilizing transient transformation of tobacco. The GUS activity driven by a PR0 promoter was detected in transgenic tobacco leaves, stem and roots, suggesting that the TkSRPP promoter was not tissue-specific. Deletion analyses in transgenic tobacco have demonstrated that the PR3 from -934 bp to -450 bp core region responded strongly to the hormones, methyl jasmonate (MeJA), abscisic acid (ABA), and salicylic acid (SA), and also to injury induction. The TkSRPP gene was highly expressed under hormones and wound-induced conditions. This study reveals the regulation pattern of the SRPP promoter, and provides valuable information for studying natural rubber biosynthesis under hormones and wounding stress.

Jasmonates in plant growth and development and elicitation of secondary metabolites: An updated overview

Secondary metabolites are incontestably key specialized molecules with proven health-promoting effects on human beings. Naturally synthesized secondary metabolites are considered an important source of pharmaceuticals, food additives, cosmetics, flavors, etc., Therefore, enhancing the biosynthesis of these relevant metabolites by maintaining natural authenticity is getting more attention. The application of exogenous jasmonates (JAs) is well recognized for its ability to trigger plant growth and development. JAs have a large spectrum of action that covers seed germination, hypocotyl growth regulation, root elongation, petal expansion, and apical hook growth. This hormone is considered as one of the key regulators of the plant's growth and development when the plant is under biotic or abiotic stress. The JAs regulate signal transduction through cross-talking with other genes in plants and thereby deploy an appropriate metabolism in the normal or stressed conditions. It has also been found to be an effective chemical elicitor for the synthesis of naturally occurring secondary metabolites. This review discusses the significance of JAs in the growth and development of plants and the successful outcomes of jasmonate-driven elicitation of secondary metabolites including flavonoids, anthraquinones, anthocyanin, xanthonoid, and more from various plant species. However, as the enhancement of these metabolites is essentially measured via in vitro cell culture or foliar spray, the large-scale production is significantly limited. Recent advancements in the plant cell culture technology lay the possibilities for the large-scale manufacturing of plant-derived secondary metabolites. With the insights about the genetic background of the metabolite biosynthetic pathway, synthetic biology also appears to be a potential avenue for accelerating their production. This review, therefore, also discussed the potential manoeuvres that can be deployed to synthesis plant secondary metabolites at the large-scale using plant cell, tissue, and organ cultures.

Transcriptome analysis reveals regulation mechanism of methyl jasmonate-induced terpenes biosynthesis in Curcuma wenyujin

Curcuma wenyujin is the source plant of three traditional Chinese medicines, which have been widely used in clinical treatment over 1000 years. The content of terpenes, the major medicinal active ingredients, is relatively low in this plant. Studies have shown that MeJA can promote terpenes biosynthesis in plants. However, the mechanism underlying the effect of MeJA in C. wenyujin remains unclear. In this work, the transcriptome of C. wenyujin leaves with MeJA treatment was analyzed to elucidate the regulation mechanism of MeJA-mediated terpene biosynthesis. Based on the RNA-seq data, 7,246 unigenes were differentially expressed with MeJA treatment. Expression pattern clustering of DEGs revealed that unigenes, related to JA biosynthesis and signal transduction, responded to exogenous MeJA stimulation on the early stage and maintained throughout the process. Subsequently, unigenes related to terpene biosynthesis pathway showed a significant up-regulation with 6 h treatment. The analysis results suggested that MeJA induced the expression of JA biosynthesis genes (such as LOXs, AOSs, AOCs, OPRs, and MFPs) and JA signal transduction core genes (JAZs and MYCs) to activate JA signaling pathway. Meanwhile, downstream JA-responsive genes presented up-regulated expression levels such as AACT, HMGSs, HMGRs, DXSs, DXRs, MCTs, HDSs, and HDRs, thus promoting terpenes biosynthesis. The transcriptional expressions of these genes were validated by qRT-PCR. In addition, six CwTPS genes in response to MeJA were identified. With MeJA treatment, the expression levels of CwTPSs were increased as well as those of the transcription factors MYB, NAC, bZIP, WRKY, AP2/ERF, and HLH. These TFs might potentially regulate terpenes biosynthesis. These results provide insights for regulation mechanism of terpenes biosynthesis.

Transcriptomic and Metabolomic Analyses Reveals That Exogenous Methyl Jasmonate Regulates Galanthamine Biosynthesis in Lycoris longituba Seedlings

The Amaryllidaceae alkaloid galanthamine (Gal) in Lycoris longituba is a secondary metabolite that has been used to treat Alzheimer's disease. Plant secondary metabolism is affected by methyl jasmonate (MeJA) exposure, although the regulatory mechanisms of MeJA on L. longituba seedlings remains largely unknown. In the present study, 75, 150, and 300 μM MeJA were used as treatments on L. longituba seedlings for 7, 14, 21, and 28 days, while 0 μM MeJA was used as the control (MJ-0). The effect of exogenous MeJA on Gal synthesis in L. longituba was then investigated using transcriptomic sequencing and metabolite profiling via GC-MS and LC-MS analysis. Galanthamine (Gal), lycorine (Lyc), and lycoramine (Lycm) abundances were 2. 71-, 2. 01-, and 2.85-fold higher in 75 μM MeJA (MJ-75) treatment plants compared to MJ-0 treatment plants after 7 days of cultivation. Transcriptomic analysis further showed that MJ-75 treatment significantly induced the expression of norbelladine synthase (NBS) and norbelladine 4'-O-methyltransferase (OMT), which are involved in the Gal biosynthesis pathway. In addition, increased expression was observed in MJ-75 treatment plants for genes in the JA synthesis and JA signaling pathways including those of allene oxide cyclase (AOC), 12-oxo-phytodienoic acid reductase (OPR), jasmonic acid amino acid synthase (JAR), and transcription factor MYC. The L. longituba tyrosine decarboxylase (LlTYDC) enzyme was identified and proposed to be involved in the Gal biosynthetic pathway. Metabolomics results demonstrated that the accumulation of Amaryllidaceae alkaloids, and especially alkaloids in the Gal biosynthesis pathway, could be induced by MJ-75 treatment. Interestingly, metabolites in the JA synthesis pathway were also affected by MeJA treatment. Overall, this multi-omics study suggests that both the JA synthesis/JA signaling and Gal biosynthesis pathways were affected by exogenous MeJA treatment. This comprehensive study of gene expression and metabolite contents can help us better understand the molecular mechanisms underlying MeJA-mediated Gal biosynthesis in L. longituba.

Heterologous activation of the Hevea PEP16 promoter in the rubber-producing laticiferous tissues of Taraxacum kok-saghyz

Hevea brasiliensis, the most abundant rubber crop, is used widely for the commercial production of natural rubber. To reduce the risk of a shortage in the supply of natural rubber that may arise from a single major rubber crop, rubber dandelion (Taraxacum kok-saghyz) has been developed as an alternative rubber-producing crop by using a transgenic approach. However, it is necessary to identify a suitable promoter for the transfer of rubber biosynthesis-related genes to the species. In this study, the promoter region of H. brasiliensis PEP16, which was isolated as a potentially important component in rubber biosynthesis, was sequenced and a pPEP16::GUS fusion construct was introduced into T. kok-saghyz. Histological and fluorometric studies using transgenic T. kok-saghyz plants indicated that the HbPEP16 promoter was highly activated in a laticiferous tissue-specific manner under normal growth conditions and that promoter activation was tightly regulated by various hormones and external signals. These findings suggested that the HbPEP16 promoter may be a useful molecular tool for the manipulation of gene expression in the laticiferous tissues of T. kok-saghyz.

Regulatory Potential of bHLH-Type Transcription Factors on the Road to Rubber Biosynthesis in Hevea brasiliensis

Natural rubber is the main component of latex obtained from laticifer cells of Hevea brasiliensis. For improving rubber yield, it is essential to understand the genetic molecular mechanisms responsible for laticifer differentiation and rubber biosynthesis. Jasmonate enhances both secondary laticifer differentiation and rubber biosynthesis. Here, we carried out time-course RNA-seq analysis in suspension-cultured cells treated with methyljasmonic acid (MeJA) to characterize the gene expression profile. Gene Ontology (GO) analysis showed that the term "cell differentiation" was enriched in upregulated genes at 24 hours after treatment, but inversely, the term was enriched in downregulated genes at 5 days, indicating that MeJA could induce cell differentiation at an early stage of the response. Jasmonate signaling is activated by MYC2, a basic helix-loop-helix (bHLH)-type transcription factor (TF). The aim of this work was to find any links between transcriptomic changes after MeJA application and regulation by TFs. Using an in vitro binding assay, we traced candidate genes throughout the whole genome that were targeted by four bHLH TFs: Hb_MYC2-1, Hb_MYC2-2, Hb_bHLH1, and Hb_bHLH2. The latter two are highly expressed in laticifer cells. Their physical binding sites were found in the promoter regions of a variety of other TF genes, which are differentially expressed upon MeJA exposure, and rubber biogenesis-related genes including SRPP1 and REF3. These studies suggest the possibilities that Hb_MYC2-1 and Hb_MYC2-2 regulate cell differentiation and that Hb_bHLH1 and Hb_bHLH2 promote rubber biosynthesis. We expect that our findings will help to increase natural rubber yield through genetic control in the future.

Identification and evaluation of suitable reference genes for gene expression analysis in rubber tree leaf

Gene expression profiles are increasingly applied to investigate molecular mechanism for which, normalization with suitable reference genes is critical. Previously we have reported several suitable reference genes for laticifer samples from rubber tree, however, little is known in leaf. The main objective of this current study was to identify some stable expression reference genes at various developmental stages of leaf, as well as during abiotic (high and low temperature extremes) and biotic stresses (pathogen stress). Gene expression profilings identified the ubiquitin-proteasome system as excellent potential as reference genes for rubber tree leaf. Among a total of 30 tested genes investigated, 24 new candidate (including 11 genes involved in the ubiquitin-proteasome system), 4 previously identified and 2 specific genes, were further evaluated using quantitative real-time PCR. Our results indicated that the new candidate genes had better expression stability comparing with others. For instance, an ubiquitin conjugating enzyme (RG0099) and three ubiquitin-protein ligases (RG0928, RG2190 and RG0118) expressed stably in all samples, and were confirmed to be suitable reference genes for rubber tree leaf under four different conditions. Finally, we suggest that using more than one reference gene may be appropriate in gene expression studies when employing different software to normalize gene expression data. Our findings have significant implications for the reliability of data obtained from genomics studies in rubber tree and perhaps in other species.

Comparative transcriptomic analysis reveal the regulation mechanism underlying MeJA-induced accumulation of alkaloids in Dendrobium officinale

Dendrobium officinale is a traditional medicinal herb with a variety of bioactive components. Alkaloid is one of the major active ingredients of Dendrobium plants, and its immune regulatory effects have been well-studied. Although a number of genes involved in the biosynthetic pathway of alkaloids have been elucidated, the regulation mechanism underlying the methyl-jasmonate (MeJA)-induced accumulation of alkaloids in D. officinale is largely unknown. In our study, a total of 4,857 DEGs, including 2,943 up- and 1,932 down-regulated genes, were identified between the control and MeJA-treated groups. Kyoto Encyclopedia of Genes and Genomes annotation showed that a number of DEGs were associated with the putative alkaloid biosynthetic pathway in D. officinale. The main group of Dendrobium alkaloids are sesquiterpene alkaloids, which are the downstream products of mevalonate (MVA) and methylerythritol 4-phosphate (MEP) pathway. Several MVA and MEP pathway genes were significantly up-regulated by the MeJA treatment, suggesting an active precursor supply for the alkaloid biosynthesis under MeJA treatment. A number of MeJA-induced P450 family genes, aminotransferase genes and methyltransferase genes were identified, providing several important candidates to further elucidate the sesquiterpene alkaloid biosynthetic pathway of D. officinale. Furthermore, a large number of MeJA-induced transcript factor encoding genes were identified, suggesting a complex genetic network affecting the sesquiterpene alkaloid metabolism in D. officinale. Our data aids to reveal the regulation mechanism underlying the MeJA-induced accumulation of sesquiterpene alkaloids in D. officinale.

Comparative transcriptomic analysis reveal the regulation mechanism underlying MeJA-induced accumulation of alkaloids in Dendrobium officinale

Dendrobium officinale is a traditional medicinal herb with a variety of bioactive components. Alkaloid is one of the major active ingredients of Dendrobium plants, and its immune regulatory effects have been well-studied. Although a number of genes involved in the biosynthetic pathway of alkaloids have been elucidated, the regulation mechanism underlying the methyl-jasmonate (MeJA)-induced accumulation of alkaloids in D. officinale is largely unknown. In our study, a total of 4,857 DEGs, including 2,943 up- and 1,932 down-regulated genes, were identified between the control and MeJA-treated groups. Kyoto Encyclopedia of Genes and Genomes annotation showed that a number of DEGs were associated with the putative alkaloid biosynthetic pathway in D. officinale. The main group of Dendrobium alkaloids are sesquiterpene alkaloids, which are the downstream products of mevalonate (MVA) and methylerythritol 4-phosphate (MEP) pathway. Several MVA and MEP pathway genes were significantly up-regulated by the MeJA treatment, suggesting an active precursor supply for the alkaloid biosynthesis under MeJA treatment. A number of MeJA-induced P450 family genes, aminotransferase genes and methyltransferase genes were identified, providing several important candidates to further elucidate the sesquiterpene alkaloid biosynthetic pathway of D. officinale. Furthermore, a large number of MeJA-induced transcript factor encoding genes were identified, suggesting a complex genetic network affecting the sesquiterpene alkaloid metabolism in D. officinale. Our data aids to reveal the regulation mechanism underlying the MeJA-induced accumulation of sesquiterpene alkaloids in D. officinale.