Accumulation of phenylpropanoids and correlated gene expression in hairy roots of tartary buckwheat under light and dark conditions

Metabolome analysis reveals flavonoid changes during the leaf color transition in Populus × euramericana 'Zhonghuahongye'

Introduction

To investigate the mechanism of leaf color change at different stages in Populus × euramericana 'Zhonghuahongye' ('Zhonghong' poplar).

Methods

Leaf color phenotypes were determined and a metabolomic analysis was performed on leaves at three stages (R1, R2 and R3).

Results

The a*, C* and chromatic light values of the leaves decreased by 108.91%, 52.08% and 113.34%, while the brightness L values and chromatic b* values gradually increased by 36.01% and 13.94%, respectively. In the differential metabolite assay, 81 differentially expressed metabolites were detected in the R1 vs. R3 comparison, 45 were detected in the R1 vs. R2 comparison, and 75 were detected in the R2 vs. R3 comparison. Ten metabolites showed significant differences in all comparisons, which were mostly flavonoid metabolites. The metabolites that were upregulated in the three periods were cyanidin 3,5-O-diglucoside, delphinidin, and gallocatechin, with flavonoid metabolites accounting for the largest proportion and malvidin 3- O-galactoside as the primary downregulated metabolite. The color shift of red leaves from a bright purplish red to a brownish green was associated with the downregulation of malvidin 3-O-glucoside, cyanidin, naringenin, and dihydromyricetin.

Discussion

Here, we analyzed the expression of flavonoid metabolites in the leaves of 'Zhonghong' poplar at three stages and identified key metabolites closely related to leaf color change, providing an important genetic basis for the genetic improvement of this cultivar.

Impact of Light and Dark Treatment on Phenylpropanoid Pathway Genes, Primary and Secondary Metabolites in Agastache rugosa Transgenic Hairy Root Cultures by Overexpressing Arabidopsis Transcription Factor AtMYB12

Agastache rugosa, otherwise called Korean mint, has a wide range of medicinal benefits. In addition, it is a rich source of several medicinally valuable compounds such as acacetin, tilianin, and some phenolic compounds. The present study aimed to investigate how the Tartary buckwheat transcription factor AtMYB12 increased the primary and secondary metabolites in Korean mint hairy roots cultured under light and dark conditions. A total of 50 metabolites were detected by using high-performance liquid chromatography (HPLC) and gas chromatography-time-of-flight mass spectrometry (GC-TOFMS). The result showed that the AtMYB12 transcription factor upregulated the phenylpropanoid biosynthesis pathway genes, which leads to the highest accumulation of primary and secondary metabolites in the AtMYB12-overexpressing hairy root lines (transgenic) than that of the GUS-overexpressing hairy root line (control) when grown under the light and dark conditions. However, when the transgenic hairy root lines were grown under dark conditions, the phenolic and flavone content was not significantly different from that of the control hairy root lines. Similarly, the heat map and hierarchical clustering analysis (HCA) result showed that most of the metabolites were significantly abundant in the transgenic hairy root cultures grown under light conditions. Principal component analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) showed that the identified metabolites were separated far based on the primary and secondary metabolite contents present in the control and transgenic hairy root lines grown under light and dark conditions. Metabolic pathway analysis of the detected metabolites showed 54 pathways were identified, among these 30 were found to be affected. From these results, the AtMYB12 transcription factor activity might be light-responsive in the transgenic hairy root cultures, triggering the activation of the primary and secondary metabolic pathways in Korean mint.

Hairy Root Cultures as a Source of Polyphenolic Antioxidants: Flavonoids, Stilbenoids and Hydrolyzable Tannins

Due to their chemical properties and biological activity, antioxidants of plant origin have gained interest as valuable components of the human diet, potential food preservatives and additives, ingredients of cosmetics and factors implicated in tolerance mechanisms against environmental stress. Plant polyphenols are the most prominent and extensively studied, albeit not only group of, secondary plant (specialized) metabolites manifesting antioxidative activity. Because of their potential economic importance, the productive and renewable sources of the compounds are desirable. Over thirty years of research on hairy root cultures, as both producers of secondary plant metabolites and experimental systems to investigate plant biosynthetic pathways, brought about several spectacular achievements. The present review focuses on the Rhizobium rhizogenes-transformed roots that either may be efficient sources of plant-derived antioxidants or were used to elucidate some regulatory mechanisms responsible for the enhanced accumulation of antioxidants in plant tissues.

Biotechnological Methods for Buckwheat Breeding

The Fagopyrum genus includes two cultivated species, namely common buckwheat (F. esculentum Moench) and Tartary buckwheat (F. tataricum Gaertn.), and more than 25 wild buckwheat species. The goal of breeders is to improve the properties of cultivated buckwheat with methods of classical breeding, with the support of biotechnological methods or a combination of both. In this paper, we reviewed the possibility to use transcriptomics, genomics, interspecific hybridization, tissue cultures and plant regeneration, molecular markers, genetic transformation, and genome editing to aid in both the breeding of buckwheat and in the identification and production of metabolites important for preserving human health. The key problems in buckwheat breeding are the unknown mode of inheritance of most traits, associated with crop yield and the synthesis of medicinal compounds, low seed yield, shedding of seeds, differential flowering and seed set on branches, and unknown action of genes responsible for the synthesis of buckwheat metabolites of pharmaceutical and medicinal interest.

Effect of Light and Dark on the Phenolic Compound Accumulation in Tartary Buckwheat Hairy Roots Overexpressing ZmLC

Fagopyrum tataricum ‘Hokkai T10′ is a buckwheat cultivar capable of producing large amounts of phenolic compounds, including flavonoids (anthocyanins), phenolic acids, and catechin, which have antioxidant, anticancer, and anti-inflammatory properties. In the present study, we revealed that the maize transcription factor Lc increased the accumulation of phenolic compounds, including sinapic acid, 4-hydroxybenzonate, t-cinnamic acid, and rutin, in Hokkai T10 hairy roots cultured under long-photoperiod (16 h light and 8 h dark) conditions. The transcription factor upregulated phenylpropanoid and flavonoid biosynthesis pathway genes, yielding total phenolic contents reaching 27.0 ± 3.30 mg g⁻¹ dry weight, 163% greater than the total flavonoid content produced by a GUS-overexpressing line (control). In contrast, when cultured under continuous darkness, the phenolic accumulation was not significantly different between the ZmLC-overexpressing hairy roots and the control. These findings suggest that the transcription factor (ZmLC) activity may be light-responsive in the ZmLC-overexpressing hairy roots of F. tataricum, triggering activation of the phenylpropanoid and flavonoid biosynthesis pathways. Further studies are required on the optimization of light intensity in ZmLC-overexpressing hairy roots of F. tataricum to enhance the production of phenolic compounds.

Genome-Wide Investigation of Major Enzyme-Encoding Genes in the Flavonoid Metabolic Pathway in Tartary Buckwheat (Fagopyrum tataricum)

Key enzymes play a vital role in plant growth and development. However, the evolutionary relationships between genes encoding key enzymes in the metabolic pathway of Tartary buckwheat flavonoids are poorly understood. Based on the published Tartary buckwheat genome sequence and related Tartary buckwheat transcriptome data, 48 key enzyme-encoding genes involved in flavonoid metabolism were screened from the Tartary buckwheat genome in this study; the chromosome localization, gene structure and promoter elements of these enzyme-encoding gene were also investigated. Gene structure analysis revealed relatively conserved 5' exon sequences among the 48 genes, indicating that the structural diversity of key enzyme-encoding genes is low in Tartary buckwheat. Through promoter analysis, these key enzyme-encoding genes were found to contain a large number of light-response elements and hormone-response elements. In addition, some genes could bind MYB transcription factors, participating in the regulation of flavonoid biosynthesis. The transcription level of the 48 key enzyme-encoding gene varied greatly among tissues. In this study, we identified 48 key enzyme-encoding genes involved in flavonoid metabolic pathways, and elucidated the structure, evolution and tissue-specific expression patterns of these genes. These results lay a foundation for further understanding the functional characteristics and evolutionary relationships of key enzyme-encoding genes involved in the flavonoid metabolic pathway in Tartary buckwheat.

Effect of microwave radiation on antioxidant capacities of Tartary buckwheat sprouts

This study aimed to investigate the effects of different microwave radiation power and treatment time on the antioxidant enzyme activities and radical scavenging potency in Tartary buckwheat sprouts. The results indicated that the optimal microwave irradiation conditions for superoxide dismutase, catalase, peroxidise and ascorbate peroxidise antioxidant enzymes was the power 300 W for 75 s, and their activities were all higher than those of the control and the ungerminated seeds. In addition, under the above microwave conditions, the total reducing power and the ability to scavenge DPPH, ABTS, O₂- and •OH were also optimal. These results indicated that suitable microwave treatment could effectively improve the antioxidant enzyme activity in Tartary buckwheat sprouts and enhance the antioxidant capacity of sprouts.

TrMYB4 transcription factor regulates the rutin biosynthesis in hairy roots of F. cymosum

Fagopyrum cymosum has been considered as a traditional medicinal plant that belongs to Fagopyrum, which has exhibited great pharmaceutical potential due to its abundant flavonoid accumulation. The hairy roots induced by Agrobacterium rhizogenes has been utilized to produce valuable specialized metabolites or reveals plant metabolic processes, whereas the underlying regulatory networks of flavonoid biosynthesis in hairy roots of F. cymosum remained unexplored. Here, the regulatory transcription factor TrMYB4 cloned from Trifolium repens with purple striped leaves was considered to investigate the mechanism of flavonoids biosynthesis in hairy roots of F. cymosum. Results showed that the expression of key genes involved in rutin biosynthesis pathway from TrMYB4 hairy roots were significantly up-regulated compared with non-transgenic hairy roots, while the content of total flavonoids and rutin in TrMYB4 hairy roots also increased consistently. It revealed the TrMYB4 transcription factor could regulate the rutin biosynthesis in F. cymosum. Meanwhile, our research provided a theoretical reference for the industrial production of rutin using F. cymosum hairy roots.

Study of the Variation of Phenolic Acid and Flavonoid Content from Fresh Artemisiae argyi Folium to Moxa Wool

Artemisiae argyi Folium (AAF) is a popular herbal medicine that is always employed in moxa sticks and by oral dosage in clinical use. Less attention has been paid to nonvolatile compounds as active compounds, such as phenolic acids and flavonoids. In this study, we focused on the variation rule of phenolic acids and flavonoids in the various transformations of Artemisiae argyi Folium. Using the established ultra-performance liquid chromatography (UPLC) method with an excellent methodology under “spider-web” mode, six phenolic acids and three flavonoids were simultaneously quantified in fresh and drying Artemisiae argyi Folium as well as in moxa wool and residue. Some interesting phenomena about the variation rule of phenolic acids and flavonoids were uncovered. First, a sharp increase was observed in the detected compounds’ content as the moisture gradually decreased, when fresh Artemisiae argyi Folium was exposed to sunlight and ambient or high temperature. Nevertheless, the increased phenolic acids were subjected to high temperature, leading to obvious degradation under oven-drying (60 °C and 80 °C). Second, a wide content distribution was revealed for the detected compounds in Artemisiae argyi Folium from different habitats, especially rutin, caffeic acid, chlorogenic acid, jaceosidin, eupatilin, and cryptochlorogenic acid. Third, accompanied by the elevated ratio of Artemisiae argyi Folium/moxa wool, the detected compounds conspicuously decreased in moxa wool and the correspondingly removed powder as residue. Importantly, a greater variation was found in moxa wool. Our findings contribute to the optimization of the drying process, the quality evaluation of the various transformations of Artemisiae argyi Folium, and the distinctive characterization of moxa wool produced at different ratios of Artemisiae argyi Folium/moxa wool.

Influence of Culture Medium Composition and Light Conditions on the Accumulation of Bioactive Compounds in Shoot Cultures of Scutellaria lateriflora L. (American Skullcap) Grown In Vitro

Methanolic extracts from in vitro grown Scutellaria lateriflora shoots cultured on five Murashige and Skoog (MS) medium variants supplemented with different combinations of 6-benzylaminopurine (BAP) and α-naphthaleneacetic acid (NAA) under different light conditions (monochromatic light, white light and no light) were analysed by HPLC for three groups of metabolites: flavonoids (26 compounds), phenolic acids and their precursors (19+2) and phenylethanoid glycosides (2). The analyses revealed the presence of baicalein, baicalin, wogonin, wogonoside, 3,4-dihydroxyphenylacetic acid and verbascoside. There was clear evidence of the influence of plant growth regulators and light conditions on the accumulation of the analysed groups of secondary metabolites. The amounts of the compounds changed within a wide range—for the total flavonoid content, 30.2-fold (max. 1204.3 mg·100 g⁻¹ dry weight (DW)); for 3,4-dihydroxyphenylacetic acid, 5.5-fold (max. 33.56 mg·100 g⁻¹ DW); and for verbascoside, 1.5-fold (169.15 max. mg·100 g⁻¹ DW). The best medium for the production of most of the compounds was the Murashige and Skoog variant with 1 mg l⁻¹ BAP and 1 mg l⁻¹ NAA. For verbascoside, the best ‘productive’ medium was the MS variant supplemented with 0.5 mg l⁻¹ BAP and 2 mg l⁻¹ NAA. The accumulation of the metabolites was stimulated to the greatest extent by blue light, under which the extracts were found to contain the highest total amount of flavonoids and the highest amounts of flavonoid glucuronides, baicalin and wogonoside, as well as of verbascoside. Their amounts were, respectively, 1.54-, 1.49-, 2.05- and 1.86-fold higher than under the control white light.

Production of glucosinolates, phenolic compounds and associated gene expression profiles of hairy root cultures in turnip (Brassica rapa ssp. rapa)

Turnip (Brassica rapa ssp. rapa) is an important vegetable crop producing glucosinolates (GSLs) and phenolic compounds. The GSLs, phenolic compound contents and transcript levels in hairy root cultures, as well as their antioxidant, antimicrobial and anticancer activity were studied in turnip. Transgenic hairy root lines were confirmed by polymerase chain reaction (PCR) and reverse transcription-PCR. GSLs levels (glucoallysin, glucobrassicanapin, gluconasturtiin, glucobrassicin, 4-methoxyglucobrassicin, neoglucobrassicin and 4-hydroxyglucobrassicin) and their gene expression levels (BrMYB28, BrMYB29, BrMYB34, BrMYB51, BrMYB122, CYP79 and CYP83) significantly increased in hairy roots compared with that in non-transformed roots. Furthermore, hairy roots efficiently produced several important individual phenolic compounds (flavonols, hydroxybenzoic and hydroxycinnamic acids). Colorimetric analysis revealed that the highest levels of total phenol, flavonoid contents, and their gene expression levels (PAL, CHI and FLS) in hairy roots than non-transformed roots. Our study provides beneficial information on the molecular and physiological active processes that are associated with the phytochemical content and biosynthetic gene expression in turnip. Moreover, antioxidant activity, as measured by DPPH scavenging activity, reducing potential, phosphomolybdenum and ferrous ion chelating ability assays was significantly higher in hairy roots. Hairy root extracts exhibited higher antimicrobial activity against bacterial and fungal species. The extract of hairy roots showed inhibition of human breast and colon cancer cell lines.

Exogenous isoprene modulates gene expression in unstressed Arabidopsis thaliana plants

Isoprene is a well-studied volatile hemiterpene that protects plants from abiotic stress through mechanisms that are not fully understood. The antioxidant and membrane stabilizing potential of isoprene are the two most commonly invoked mechanisms. However, isoprene also affects phenylpropanoid metabolism, suggesting an additional role as a signalling molecule. In this study, microarray-based gene expression profiling reveals transcriptional reprogramming of Arabidopsis thaliana plants fumigated for 24 h with a physiologically relevant concentration of isoprene. Functional enrichment analysis of fumigated plants revealed enhanced heat- and light-stress-responsive processes in response to isoprene. Isoprene induced a network enriched in ERF and WRKY transcription factors, which may play a role in stress tolerance. The isoprene-induced up-regulation of phenylpropanoid biosynthetic genes was specifically confirmed using quantitative reverse transcription polymerase chain reaction. These results support a role for isoprene as a signalling molecule, in addition to its possible roles as an antioxidant and membrane thermoprotectant.