Identification and functional characterization of RsGST1, an anthocyanin-related glutathione S-transferase gene in radish

Integration of Metabolomic and Transcriptomic Analyses Reveals the Molecular Mechanisms of Flower Color Formation in Prunus mume

Flower color is an important trait that affects the economic value of Prunus mume, a famous ornamental plant in the Rosaceae family. P. mume with purple-red flowers is uniquely charming and highly favored in landscape applications. However, little is known about its flower coloring mechanism, which stands as a critical obstacle on the path to innovative breeding for P. mume flower color. In this study, transcriptomic and targeted metabolomic analyses of purple-red P. mume and white P. mume were performed to elucidate the mechanism of flower color formation. In addition, the expression patterns of key genes were analyzed using an RT-qPCR experiment. The results showed that the differential metabolites were significantly enriched in the flavonoid synthesis pathway. A total of 14 anthocyanins emerged as the pivotal metabolites responsible for the differences in flower color between the two P. mume cultivars, comprising seven cyanidin derivatives, five pelargonium derivatives, and two paeoniflorin derivatives. Moreover, the results clarified that the metabolic pathway determining flower color in purple-red P. mume encompasses two distinct branches: cyanidin and pelargonidin, excluding the delphinidin branch. Additionally, through the integrated analysis of transcriptomic and metabolomic data, we identified 18 key genes responsible for anthocyanin regulation, thereby constructing the gene regulatory network for P. mume anthocyanin synthesis. Among them, ten genes (PmCHI, PmGT2, PmGT5, PmGST3, PmMYB17, PmMYB22, PmMYB23, PmbHLH4, PmbHLH10, and PmbHLH20) related to anthocyanin synthesis were significantly positively correlated with anthocyanin contents, indicating that they may be the key contributors to anthocyanin accumulation. Our investigation contributes a novel perspective to understanding the mechanisms responsible for flower color formation in P. mume. The findings of this study introduce novel strategies for molecular design breeding aimed at manipulating flower color in P. mume.

NtERF4 promotes the biosynthesis of chlorogenic acid and flavonoids by targeting PAL genes in Nicotiana tabacum

Chlorogenic acid (CGA) and flavonoids are important secondary metabolites, which modulate plant growth and development, and contribute to plant resistance to various environmental stresses. ERF4 has been shown to be a repressor of anthocyanin accumulation in grape, but its full roles in regulating the biosynthesis of other phenylpropanoid compounds still needs to be further studied. In the present study, two NtERF4 genes were identified from N. tabacum genome. The expression level of NtERF4a was higher than that of NtERF4b in all the tobacco tissues examined. Over-expression of NtERF4a significantly promoted the accumulation of CGA and flavonoids in tobacco leaves, while silencing of NtERF4a significantly repressed the biosynthesis of CGA and flavonoids. RNA-seq analysis of NtERF4a-OE and WT plants revealed 8 phenylpropanoids-related differentially expressed genes (DEGs), including 4 NtPAL genes that encode key enzymes in the phenylpropanoid pathway. Activation of NtERF4a-GR fusion protein in tobacco significantly induced the transcription of NtPAL1 and NtPAL2 in the presence of protein synthesis inhibitor. Chromatin immunoprecipitation and Dual-Luc assays further indicated that NtERF4a could bind to the GCC box presented in the promoters of NtPAL1 and NtPAL2, thereby activating their transcription. Moreover, ectopic expression of NtERF4a induced the transcription of NtGSK1, NtMYC2, and NtJAZ3 genes, and enhanced the resistance of tobacco seedlings to salt and drought stresses, indicating multiple roles of NtERF4a in plants. Our findings revealed new roles of NtERF4a in modulating the accumulation of phenylpropanoid compounds in tobacco, and provided a putative target for improving phenylpropanoids synthesis and stress resistance in plants.

Molecular Regulatory Network of Anthocyanin Accumulation in Black Radish Skin as Revealed by Transcriptome and Metabonome Analysis

To understand the coloring mechanism in black radish, the integrated metabolome and transcriptome analyses of root skin from a black recombinant inbred line (RIL 1901) and a white RIL (RIL 1911) were carried out. A total of 172 flavonoids were detected, and the analysis results revealed that there were 12 flavonoid metabolites in radish root skin, including flavonols, flavones, and anthocyanins. The relative concentrations of most flavonoids in RIL 1901 were higher than those in RIL 1911. Meanwhile, the radish root skin also contained 16 types of anthocyanins, 12 of which were cyanidin and its derivatives, and the concentration of cyanidin 3-o-glucoside was very high at different development stages of black radish. Therefore, the accumulation of cyanidin and its derivatives resulted in the black root skin of radish. In addition, a module positively related to anthocyanin accumulation and candidate genes that regulate anthocyanin synthesis was identified by the weighted gene co-expression network analysis (WGCNA). Among them, structural genes (RsCHS, RsCHI, RsDFR, and RsUGT75C1) and transcription factors (TFs) (RsTT8, RsWRKY44L, RsMYB114, and RsMYB308L) may be crucial for the anthocyanin synthesis in the root skin of black radish. The anthocyanin biosynthesis pathway in the root skin of black radish was constructed based on the expression of genes related to flavonoid and anthocyanin biosynthesis pathways (Ko00941 and Ko00942) and the relative expressions of metabolites. In conclusion, this study not only casts new light on the synthesis and accumulation of anthocyanins in the root skin of black radish but also provides a molecular basis for accelerating the cultivation of new black radish varieties.

The catalytic role of glutathione transferases in heterologous anthocyanin biosynthesis

Anthocyanins are ubiquitous plant pigments used in a variety of technological applications. Yet, after over a century of research, the penultimate biosynthetic step to anthocyanidins attributed to the action of leucoanthocyanidin dioxygenase has never been efficiently reconstituted outside plants, preventing the construction of heterologous cell factories. Through biochemical and structural analysis, here we show that anthocyanin-related glutathione transferases, currently implicated only in anthocyanin transport, catalyse an essential dehydration of the leucoanthocyanidin dioxygenase product, flavan-3,3,4-triol, to generate cyanidin. Building on this knowledge, introduction of anthocyanin-related glutathione transferases into a heterologous biosynthetic pathway in baker's yeast results in >35-fold increased anthocyanin production. In addition to unravelling the long-elusive anthocyanin biosynthesis, our findings pave the way for the colourants' heterologous microbial production and could impact the breeding of industrial and ornamental plants.

Genome-wide identification and characterization of Glutathione S-Transferases (GSTs) and their expression profile under abiotic stresses in tobacco (Nicotiana tabacum L.)

BACKGROUND

Glutathione S-transferases (GSTs) are large and multifunctional proteases that play an important role in detoxification, protection against biotic and abiotic stresses, and secondary metabolite transportation which is essential for plant growth and development. However, there is limited research on the identification and function of NtGSTs.

RESULTS

This study uses K326 and other six tobacco varieties (Hongda, HG, GDH11, Va116, VG, and GDH88) as materials to conduct comprehensive genome-wide identification and functional characterization of the GST gene in tobacco. A total of 59 NtGSTs were identified and classified into seven subfamilies via the whole-genome sequence analysis, with the Tau type serving as the major subfamily. The NtGSTs in the same branch of the evolutionary tree had similar exon/intron structure and motif constitution. There were more than 42 collinear blocks between tobacco and pepper, tomato, and potato, indicating high homology conservation between them. Twelve segmental duplicated gene pairs and one tandem duplication may have had a substantial impact on the evolution and expansion of the tobacco GST gene family. The RT-qPCR results showed that the expression patterns of NtGSTs varied significantly among tissues, varieties, and multiple abiotic stresses, suggesting that NtGST genes may widely respond to various abiotic stresses and hormones in tobacco, including NtGSTF4, NtGSTL1, NtGSTZ1, and NtGSTU40.

CONCLUSIONS

This study provides a comprehensive analysis of the NtGST gene family, including structures and functions. Many NtGSTs play a critical regulatory role in tobacco growth and development, and responses to abiotic stresses. These findings offer novel and valuable insights for understanding the biological function of NtGSTs and the reference materials for cultivating highly resistant varieties and enhancing the yield and quality of crops.

An investigation on glutathione derived from spinach and red cabbage leaves and their effects of adding to meat patties

Plants that produce leaves have been cultivated by humans for thousands of years because of the benefits they provide in terms of food and other necessities. Because of their high nutritional value and key phyto-components like glutathione, Leaf producing vegetables (LPVs) are being studied for their potential uses and health benefits. As a result, the focus of this study was using efficient methods for isolating and identifying glutathione from spinach and red cabbage. Glutathione was extracted using three extraction solvents: water (100%), ethanol (100%), and a combination of ethanol and water (30% and 70%, respectively) by volume (v/v), while separation was accomplished using ultrafiltration equipment. In our investigation, the best extraction solvent was a mixture of ethanol and water at a ratio of 30:70% (v/v), which extracted 951 µg/g glutathione. The antioxidant activity of plant leaf extract was measured using DPPH, with butylated hydroxytoluene serving as a comparative standard. Identification and characterization of glutathione from plant leaf extracts were revealed by thin-layer chromatography (TLC), ultraviolet-visible (UV-Vis) spectrophotometry studies, Fourier transform infrared (FTIR) spectroscopy, and high-performance liquid chromatography (HPLC). In addition, the physical and chemical properties (pH, water holding capacity, extracted liquid volume, peroxide value, free fatty acids, and thiobarbituric acid) of meat patties prepared with three different concentrations of determined glutathione were tested for susceptibility to preservation during 10 days of refrigeration at 4 ± 1 °C. The findings of the current study provide vast prospects for subsequent research to researchers and scientists that the glutathione obtained from leaf extract has no toxicity that might be applied to developed functional foods and other food formulations. Because foods containing plant-derived glutathione improve health, biological function, and food spoilage. It may be utilized as high-quality antioxidants that are safe and non-toxic. Furthermore, glutathione preserves food quality and prevents oxidation.

The long noncoding RNA LINC15957 regulates anthocyanin accumulation in radish

Radish (Raphanus sativus L.) is an important root vegetable crop belonging to the Brassicaceae family. Anthocyanin rich radish varieties are popular among consumers because of their bright color and high nutritional value. However, the underlying molecular mechanism responsible for skin and flesh induce anthocyanin biosynthesis in transient overexpression, gene silencing and transcriptome sequencing were used to verify its function in radish anthocyanin accumulation, radish remains unclear. Here, we identified a long noncoding RNA LINC15957, overexpression of LINC15957 was significantly increased anthocyanin accumulation in radish leaves, and the expression levels of structural genes related to anthocyanin biosynthesis were also significantly increased. Anthocyanin accumulation and expression levels of anthocyanin biosynthesis genes were significantly reduced in silenced LINC15957 flesh when compared with control. By the transcriptome sequencing of the overexpressed LINC15957 plants and the control, 5,772 differentially expressed genes were identified. A total of 3,849 differentially expressed transcription factors were identified, of which MYB, bHLH, WD40, bZIP, ERF, WRKY and MATE were detected and differentially expressed in the overexpressed LINC15957 plants. KEGG enrichment analysis revealed the genes were significant enriched in tyrosine, L-Phenylalanine, tryptophan, phenylpropanol, and flavonoid biosynthesis. RT-qPCR analysis showed that 8 differentially expressed genes (DEGs) were differentially expressed in LINC15957-overexpressed plants. These results suggested that LINC15957 involved in regulate anthocyanin accumulation and provide abundant data to investigate the genes regulate anthocyanin biosynthesis in radish.

Combined widely targeted metabolomics and transcriptomics analysis reveals differentially accumulated metabolites and the underlying molecular bases in fleshy taproots of distinct radish genotypes

Radish is an important taproot crop with medicinal and edible uses that is cultivated worldwide. However, the differences in metabolites and the underlying molecular bases among different radish types remain largely unknown. In the present study, a combined analysis of liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) and RNA-Seq data was conducted to uncover important differentially accumulated metabolites (DAMs) among radish accessions with green, white and red taproot flesh colours. A total of 657 metabolites were identified and 138 DAMs were commonly present in red vs. green and red vs. white accessions. Red accessions were rich in phenolic compounds, while green and white accessions had more amino acids. Additionally, 41 metabolites and 98 genes encoding 37 enzymes were enriched in the shikimate and phenolic biosynthesis pathways. CHS is the rate-limiting enzyme determining flavonoid differences among accessions. A total of 119 candidate genes might contribute to red accession-specific accumulated metabolites. Specifically, one gene cluster consisting of 16 genes, including one RsMYB1, RsMYBL2, RsTT8, RsDFR, RsANS, Rs4CL3, RsSCPL10, Rs3AT1 and RsSAP2 gene, two RsTT19 and RsWRKY44 genes and three RsUGT genes, might be involved in anthocyanin accumulation in red radish fleshy taproots. More importantly, an InDel marker was developed based on an RsMYB1 promoter mutation, and the accuracy reached 95.9% when it was used to select red-fleshed radishes. This study provides comprehensive insights into the metabolite differences and underlying molecular mechanisms in fleshy taproots among different radish genotypes and will be beneficial for the genetic improvement of radish nutritional quality.

Functional Characterization of MtrGSTF7, a Glutathione S-Transferase Essential for Anthocyanin Accumulation in Medicago truncatula

Flavonoids are essential compounds widespread in plants and exert many functions such as defence, definition of organ colour and protection against stresses. In Medicago truncatula, flavonoid biosynthesis and accumulation is finely regulated in terms of tissue specificity and induction by external factors, such as cold and other stresses. Among flavonoids, anthocyanin precursors are synthesised in the cytoplasm, transported to the tonoplast, then imported into the vacuole for further modifications and storage. In the present work, we functionally characterised MtrGSTF7, a phi-class glutathione S-transferase involved in anthocyanin transport to the tonoplast. The mtrgstf7 mutant completely lost the ability to accumulate anthocyanins in leaves both under control and anthocyanin inductive conditions. On the contrary, this mutant showed an increase in the levels of soluble proanthocyanidins (Pas) in their seeds with respect to the wild type. By complementation and expression data analysis, we showed that, differently from A. thaliana and similarly to V. vinifera, transport of anthocyanin and proanthocyanidins is likely carried out by different GSTs belonging to the phi-class. Such functional diversification likely results from the plant need to finely tune the accumulation of diverse classes of flavonoids according to the target organs and developmental stages.

Biochemistry and Molecular Basis of Intracellular Flavonoid Transport in Plants

Flavonoids are a biochemically diverse group of specialized metabolites in plants that are derived from phenylalanine. While the biosynthesis of the flavonoid aglycone is highly conserved across species and well characterized, numerous species-specific decoration steps and their relevance remained largely unexplored. The flavonoid biosynthesis takes place at the cytosolic side of the endoplasmatic reticulum (ER), but accumulation of various flavonoids was observed in the central vacuole. A universal explanation for the subcellular transport of flavonoids has eluded researchers for decades. Current knowledge suggests that a glutathione S-transferase-like protein (ligandin) protects anthocyanins and potentially proanthocyanidin precursors during the transport to the central vacuole. ABCC transporters and to a lower extend MATE transporters sequester anthocyanins into the vacuole. Glycosides of specific proanthocyanidin precursors are sequestered through MATE transporters. A P-ATPase in the tonoplast and potentially other proteins generate the proton gradient that is required for the MATE-mediated antiport. Vesicle-mediated transport of flavonoids from the ER to the vacuole is considered as an alternative or additional route.