Unraveling the functional characterization of a jasmonate-induced flavonoid biosynthetic CYP45082G24 gene in Carthamus tinctorius

The cytochrome P450 superfamily of monooxygenases plays a major role in the evolution and diversification of plant natural products. The function of cytochrome P450s in physiological adaptability, secondary metabolism, and xenobiotic detoxification has been studied extensively in numerous plant species. However, their underlying regulatory mechanism in safflower still remained unclear. In this study, we aimed to elucidate the functional role of a putative CtCYP82G24-encoding gene in safflower, which suggests crucial insights into the regulation of methyl jasmonate-induced flavonoid accumulation in transgenic plants. The results showed that methyl jasmonate (MeJA) was associated with a progressive upregulation of CtCYP82G24 expression in safflower among other treatment conditions including light, dark, and polyethylene glycol (PEG). In addition, transgenic plants overexpressing CtCYP82G24 demonstrated increased expression level of other key flavonoid biosynthetic genes, such as AtDFR, AtANS, and AtFLS, and higher content of flavonoid and anthocyanin accumulation when compared with wild-type and mutant plants. Under exogenous MeJA treatment, the CtCYP82G24 transgenic overexpressed lines showed a significant spike in flavonoid and anthocyanin content compared with wild-type and mutant plants. Moreover, the virus-induced gene silencing (VIGS) assay of CtCYP82G24 in safflower leaves exhibited decreased flavonoid and anthocyanin accumulation and reduced expression of key flavonoid biosynthetic genes, suggesting a possible coordination between transcriptional regulation of CtCYP82G24 and flavonoid accumulation. Together, our findings confirmed the likely role of CtCYP82G24 during MeJA-induced flavonoid accumulation in safflower.

Combined metabolomics and transcriptomics analysis reveals the mechanism underlying blue light-mediated promotion of flavones and flavonols accumulation in Ligusticum chuanxiong Hort. microgreens

Ligusticum chuanxiong Hort. (Chuanxiong) is an important Chinese medicinal herb, whose rhizomes are widely used as raw materials for treating various diseases caused by blood stasis. The fresh tender stems and leaves of Chuanxiong are also consumed and have the potential as microgreens. Here, we investigated the effect of light spectra on yield and total flavonoid content of Chuanxiong microgreens by treatment with LED-based white light (WL), red light (RL), blue light (BL), and continuous darkness (DD). The results showed that WL and BL reduced biomass accumulation but significantly increased total flavonoid content compared to RL or DD treatments. Widely targeted metabolomics analysis confirmed that BL promoted the accumulation of flavones and flavonols in Chuanxiong microgreens. Further integration of transcriptomics and metabolomics analysis revealed the mechanism by which BL induces the up-regulation of transcription factors such as HY5 and MYBs, promotes the expression of key genes targeted for flavonoid biosynthesis, and ultimately leads to the accumulation of flavones and flavonols. This study suggests that blue light is a proper light spectra to improve the quality of Chuanxiong microgreens, and the research results lay a foundation for guiding the de-etiolation of Chuanxiong microgreens to obtain both yield and quality in production practice.

Carbon and nitrogen metabolism under nitrogen variation affects flavonoid accumulation in the leaves of Coreopsis tinctoria

Flavonoids are phytochemicals present in medicinal plants and contribute to human health. Coreopsis tinctoria, a species rich in flavonoids, has long been used in traditional medicine and as a food resource. N (nitrogen) fertilization can reduce flavonoid accumulation in C. tinctoria. However, there is limited knowledge regarding N regulatory mechanisms. The aim of this study was to determine the effect of N availability on flavonoid biosynthesis in C. tinctoria and to investigate the relationship between C (carbon) and N metabolism coupled with flavonoid synthesis under controlled conditions. C. tinctoria seedlings were grown hydroponically under five different N levels (0, 0.625, 1.250, 2.500 and 5.000 mM). The related indexes of C, N and flavonoid metabolism of C. tinctoria under N variation were measured and analysed. N availability (low and moderate N levels) regulates enzyme activities related to C and N metabolism, promotes the accumulation of carbohydrates, reduces N metabolite levels, and enhances the internal C/N balance. The flavonoid content in roots and stalks remained relatively stable, while that in leaves peaked at low or intermediate N levels. Flavonoids are closely related to phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), 4-coumarate: coenzyme A ligase (4CL), and chalcone-thioase (CHS) activity, significantly positively correlated with carbohydrates and negatively correlated with N metabolites. Thus, C and N metabolism can not only control the distribution of C in amino acid and carbohydrate biosynthesis pathways but also change the distribution in flavonoid biosynthesis pathways, which also provides meaningful information for maintaining high yields while ensuring the nutritional value of crop plants.

Transcriptome profiling reveals candidate flavonoid-related genes during formation of dragon's blood from Dracaena cochinchinensis (Lour.) S.C.Chen under conditions of wounding stress

ETHNOPHARMACOLOGICAL RELEVANCE

Dragon's Blood (Resina Draconis) is a red resin that has been used in traditional medicine to promote blood circulation, regenerate muscles, reduce swelling and pain, stop bleeding, etc., and its main chemical constituents are flavonoids. Dracaena cochinchinensis (Lour.) S.C.Chen is the only plant defined by the Pharmacopoeia of the People's Republic of China as a source of dragon's blood.

AIM OF THE STUDY

We aimed to reveal genes involved in the biosynthesis and accumulation of flavonoids of D. cochinchinensis which is under wounding stress by performing a de novo transcriptome analysis.

MATERIALS AND METHODS

D. cochinchinensis samples were collected for transcriptome sequencing and bioinformatics analysis at 0 days (0 d), 3 days (3 d), 6 days (6 d), and 10 days (10 d) after induction wounding stress, and tissues were microscopically observed after wounding stress.

RESULTS

A total of 63,244 unigenes were obtained through bioinformatics analysis, and genes associated with the biosynthesis of flavonoids were identified. Through the analysis of DEGs after wounding stress in D. cochinchinensis, based on gene expression consistent with flavonoid accumulation levels, 20 genes in connection with the flavonoid synthesis pathway and 56 genes that may be responsible for flavonoid modification and transport, and also revealed TFs (MYB, bHLH) that may be responsible for flavonoid biosynthesis. Analysis of DEGs between the four periods revealed that after wounding stress, the greatest number of significant DEGs were enriched during the first 3 days, while fewer DEGs were enriched after day 3, which corresponding to only about 1/10 (353/3883) the number of DEGs during the first 3 days. In addition, putative unigenes involved in lignin biosynthesis, such as CSE, HCT, CCR, F5H, and CAD, were significantly down-regulation after D. cochinchinensis wounding stress, but the putative unigenes responsible for flavonoid biosynthesis, such as CHS, CHI, DFR, F3'5'H, F3H, ANR, FLS, and ANS were significantly up-regulation.

CONCLUSION

We performed de novo transcriptome analysis of D.cochinchinensis under wounding stress, candidate genes and TFs involved in the biosynthesis and accumulation of flavonoids were identified, which is the first report on the transcript variants in flavonoid form accumulation in D. cochinchinensis under wounding stress. According to the results of DEGs analysis, wounding stress attenuated lignin biosynthesis meanwhile promoted flavonoid biosynthesis. In addition, we also compared the transcriptomics of the two different original plants (D.cochinchinensis and D.cambodiana) that form dragon's blood in order to provide further understanding of the formation of dragon's blood.

Transcriptomic analysis reveals the parallel transcriptional regulation of UV-B-induced artemisinin and flavonoid accumulation in Artemisia annua L

UV-B radiation is a pivotal photomorphogenic signal and positively regulates plant growth and metabolite biosynthesis. In order to elucidate the transcriptional regulation mechanism underlying UV-B-induced artemisinin and flavonoid biosynthesis in Artemisia annua, the transcriptional responses of A. annua L. leaves to UV-B radiation were analyzed using the Illumina transcriptome sequencing. A total of 10705 differentially expressed genes (DEGs) including 533 transcription factors (TFs), were identified. Based on the expression trends of the differentially expressed TFs as well as artemisinin and flavonoid biosynthesis genes, we speculated that TFs belonging to 6 clusters were most likely to be involved in the regulation of artemisinin and/or flavonoid biosynthesis. The regulatory relationship between TFs and artemisinin/flavonoid biosynthetic genes was further studied. Dual-LUC assays results showed that AaMYB6 is a positive regulator of AaLDOX which belongs to flavonoid biosynthesis pathway. In addition, we identified an R2R3 MYB TF, AaMYB4 which potentially mediated both artemisinin and flavonoid biosynthesis pathways by activating the expression of AaADS and AaDBR2 in artemisinin biosynthesis pathway and AaUFGT in flavonoid biosynthesis pathway. Overall, our findings would provide an insight into the elucidation of the parallel transcriptional regulation of artemisinin and flavonoid biosynthesis in A. annua L. under UV-B radiation.

Molecular characterization of flavanone 3-hydroxylase gene and flavonoid accumulation in two chemotyped safflower lines in response to methyl jasmonate stimulation

BACKGROUND

Among secondary metabolites, flavonoids are particularly crucial for plant growth, development, and reproduction, as well as beneficial for maintenance of human health. As a flowering plant, safflower has synthesized a striking variety of flavonoids with various pharmacologic properties. However, far less research has been carried out on the genes involved in the biosynthetic pathways that generate these amazing flavonoids, especially characterized quinochalcones. In this study, we first cloned and investigated the participation of a presumed flavanone 3-hydroxylase gene (F3H) from safflower (CtF3H) in a flavonoid biosynthetic pathway.

RESULTS

Bioinformation analysis showed that CtF3H shared high conserved residues and confidence with F3H from other plants. Subcellular localization uncovered the nuclear and cytosol localization of CtF3H in onion epidermal cells. The functional expressions of CtF3H in Escherichia coli BL21(DE3)pLysS cells in the pMAL-C5x vector led to the production of dihydrokaempferol when naringenin was the substrate. Furthermore, the transcriptome expression of CtF3H showed a diametrically opposed expression pattern in a quinochalcone-type safflower line (with orange-yellow flowers) and a flavonol-type safflower line (with white flowers) under external stimulation by methyl jasmonate (MeJA), which has been identified as an elicitor of flavonoid metabolites. Further metabolite analysis showed the increasing tendency of quinochalcones and flavonols, such as hydroxysafflor yellow A, kaempferol-3-O-β-D-glucoside, kaempferol-3-O-β-rutinoside, rutin, carthamin, and luteolin, in the quinochalcone-type safflower line. Also, the accumulation of kaempferol-3-O-β-rutinoside and kaempferol-3-O-β-D-glucoside in flavonols-typed safflower line showed enhanced accumulation pattern after MeJA treatment. However, other flavonols, such as kaempferol, dihydrokaempferol and quercetin-3-O-β-D-glucoside, in flavonols-typed safflower line presented down accumulation respond to MeJA stimulus.

CONCLUSIONS

Our results showed that the high expression of CtF3H in quinochalcone-type safflower line was associated with the accumulation of both quinochalcones and flavonols, whereas its low expression did not affect the increased accumulation of glycosylated derivatives (kaempferol-3-O-β-rutinoside and rutin) in flavonols-typed safflower line but affect the upstream precursors (D-phenylalanine, dihydrokaempferol, kaempferol), which partly revealed the function of CtF3H in different phenotypes and chemotypes of safflower lines.