Molecular and biochemical characterization of the UDP-glucose: Anthocyanin 5-O-glucosyltransferase from Vitis amurensis

Systematic analysis of the UDP-glucosyltransferase family: discovery of a member involved in rutin biosynthesis in Solanum melongena

Eggplant (Solanum melongena) is an economically important crop and rich in various nutrients, among which rutin that has positive effects on human health is found in eggplant. Glycosylation mediated by UDP-glycosyltransferases (UGTs) is a key step in rutin biosynthesis. However, the UGT gene has not been reported in eggplant to date. Herein, 195 putative UGT genes were identified in eggplant by genome-wide analysis, and they were divided into 17 subgroups (Group A-P and Group R) according to the phylogenetic evolutionary tree. The members of Groups A, B, D, E and L were related to flavonol biosynthesis, and rutin was the typical flavonol. The expression profile showed that the transcriptional levels of SmUGT genes in Clusters 7-10 were closely related to those of rutin biosynthetic pathway genes. Notably, SmUGT89B2 was classified into Cluster 7 and Group B; its expression was consistent with rutin accumulation in different tissues and different leaf stages of eggplant. SmUGT89B2 was located in the nucleus and cell membrane. Virus-induced gene silencing (VIGS) and transient overexpression assays showed that SmUGT89B2 can promote rutin accumulation in eggplant. These findings provide new insights into the UGT genes in eggplant, indicating that SmUGT89B2 is likely to encode the final enzyme in rutin biosynthesis.

Ph5GT silencing alters flower color and flavonoids metabolome profile in petunia

Anthocyanins are important pigments in plants and glycosylation plays an important role in the stability of anthocyanins. Anthocyanin 5-O-glucosyltransferase (5GT) can glycosylate anthocyanin at the 5-O-position. Till now, the enzymatic activity characteristics of 5GT had been studied in vitro in a variety of plants. However, the subcellular localization of 5GT protein still remained unclear, and little genetic evidence on the roles of 5GT in plants has been reported. The full-length Ph5GT gene from petunia (Petunia hybrida) was isolated in this study. Green fluorescent fusion protein assays revealed that Ph5GT protein was localized to the cytoplasm. Ph5GT was found to be highly expressed in flowers, with highest levels of expression occurring during the coloring stage of flower development. Furthermore, Ph5GT silencing led to the change in flower color from purple to light purple and a significant reduction in total anthocyanin content. The metabolome analysis revealed that the content of malvidins and petunidins modified by glycosylation at the 5-O-position was significantly reduced, while the content of their precursor without glycosylation was significantly increased, implying that Ph5GT could glycosylate malvidin and petunidin derivatives and that the substrate types of Ph5GT were expanded in comparison to previous studies.

PhUGT78A22, a novel glycosyltransferase in Paeonia 'He Xie', can catalyze the transfer of glucose to glucosylated anthocyanins during petal blotch formation

BACKGROUND

Flower color patterns play an important role in the evolution and subsequent diversification of flowers by attracting animal pollinators. This interaction can drive the diversity observed in angiosperms today in many plant families such as Liliaceae, Paeoniaceae, and Orchidaceae, and increased their ornamental values. However, the molecular mechanism underlying the differential distribution of anthocyanins within petals remains unclear in Paeonia.

RESULTS

In this study, we used an intersectional hybrid between the section Moutan and Paeonia, hereafter named Paeonia 'He Xie', which has purple flowers with dark purple blotches. After Ultra-high performance liquid chromatography-diode array detector (UPLC-DAD) analysis of blotched and non-blotched parts of petals, we found the anthocyanin content in the blotched part was always higher than that in the non-blotched part. Four kinds of anthocyanins, namely cyanidin-3-O-glucoside (Cy3G), cyanidin-3,5-O-glucoside (Cy3G5G), peonidin-3-O-glucoside (Pn3G), and peonidin-3,5-O-glucoside (Pn3G5G) were detected in the blotched parts, while only Cy3G5G and Pn3G5G were detected in the non-blotched parts. This suggests that glucosyltransferases may play a vital role in the four kinds of glucosylated anthocyanins in the blotched parts. Moreover, 2433 differentially expressed genes (DEGs) were obtained from transcriptome analysis of blotched and non-blotched parts, and a key UDP-glycosyltransferase named PhUGT78A22 was identified, which could use Cy3G and Pn3G as substrates to produce Cy3G5G and Pn3G5G, respectively, in vitro. Furthermore, silencing of PhUGT78A22 reduced the content of anthocyanidin 3,5-O-diglucoside in P. 'He Xie'.

CONCLUSIONS

A UDP-glycosyltransferase, PhUGT78A22, was identified in P. 'He Xie', and the molecular mechanism underlying differential distribution of anthocyanins within petals was elucidated. This study provides new insights on the biosynthesis of different kinds of anthocyanins within colorful petals, and helps to explain petal blotch formation, which will facilitate the cultivar breeding with respect to increasing ornamental value. Additionally, it provides a reference for understanding the molecular mechanisms responsible for precise regulation of anthocyanin biosynthesis and distribution patterns.

Genome-wide analysis of UGT gene family identified key gene for the biosynthesis of bioactive flavonol glycosides in Epimedium pubescens Maxim

Epimedium pubescens Maxim. is a well-known traditional Chinese medicinal herb with flavonol glycosides as the major pharmaceutically active compounds. UDP-glycosyltransferases (UGTs) are a group of enzymes responsible for the glycosylation of flavonoid glycosides. In this study, a genome-wide analysis was performed to identify UGT family genes in E. pubescens. As a result, a total of 339 putative UGT genes were identified, which represents the largest UGT gene family known thus far, implying a significant expansion of the UGT gene family in E. pubescens. All EpUGTs were unevenly distributed across six chromosomes, and they were classified into 17 major groups. The expression profiles showed that UGT genes were differentially expressed in roots, leaves, flowers, shoots and fruits. In particular, several EpUGTs were highly induced by high light intensity, which was consistent with the accumulation level of bioactive flavonoids in E. pubescens. Six UGT79 genes that were preferentially expressed in roots or leaves were successfully expressed in E. coli, and only the recombinant EpGT60 protein was found to be active toward 8-prenylkaempferol and icaritin to produce the key bioactive compounds baohuoside II and baohuoside I. The optimal temperature, pH, k_m and V_max were determined for the recombinant EpGT60 protein. In addition, expression of recombinant EpGT60 in E. coli cell culture led to successful production of baohuoside II when fed 8-prenylkaempferol. Our study provides a foundation for further functional characterization of UGT genes in E. pubescens and provides key candidate genes for bioengineering bioactive flavonoids in E. pubescens.

Berry Anthocyanin, Acid, and Volatile Trait Analyses in a Grapevine-Interspecific F2 Population Using an Integrated GBS and rhAmpSeq Genetic Map

Increased map density and transferability of markers are essential for the genetic analysis of fruit quality and stress tolerance in interspecific grapevine populations. We used 1449 GBS and 2000 rhAmpSeq markers to develop a dense map for an interspecific F₂ population (VRS-F₂) that was derived by selfing a single F₁ from a Vitis riparia x ‘Seyval blanc’ cross. The resultant map contained 2519 markers spanning 1131.3 cM and was highly collinear with the Vitis vinifera ‘PN40024’ genome. Quantitative trait loci (QTL) for berry skin color and flower type were used to validate the map. Four rhAmpSeq transferable markers were identified that can be used in pairs (one pistillate and one hermaphroditic) to predict pistillate and hermaphrodite flower type with ≥99.7% accuracy. Total and individual anthocyanin diglucoside QTL mapped to chromosome 9 near a 5-O-GLUCOSYLTRANSFERASE candidate gene. Malic acid QTL were observed on chromosome 1 and 6 with two MALATE DEHYRDROGENASE CYTOPLASMIC 1 and ALUMINUM-ACTIVATED MALATE TRANSPORTER 2-LIKE (ALMT) candidate genes, respectively. Modeling malic acid identified a potential QTL on chromosome 8 with peak position in proximity of another ALMT. A first-ever reported QTL for the grassy smelling volatile (E)-2-hexenal was found on chromosome 2 with a PHOSPHOLIPID HYDROPEROXIDE GLUTATHIONE PEROXIDASE candidate gene near peak markers.

Differential Protein Expression in Berry Skin from Red Grapes with Varying Hybrid Character

Protein expression from the berry skin of four red grape biotypes with varying hybrid character was compared at a proteome-wide level to identify the metabolic pathways underlying divergent patterns of secondary metabolites. A bottom-up shotgun proteomics approach with label-free quantification and MaxQuant-assisted computational analysis was applied. Red grapes were from (i) purebred Vitis vinifera (Aglianico cv.); (ii) V. vinifera (local Sciascinoso cv.) grafted onto an American rootstock; (iii) interspecific hybrid (V. vinifera × V. labrusca, Isabel), and (iv) uncharacterized grape genotype with hybrid lineage, producing relatively abundant anthocyanidin 3,5-O-diglucosides. Proteomics supported the differences between hybrids and purebred V. vinifera grapes, consistently with distinct phenotypic metabolite assets. Methanol O-anthraniloyltransferase, which catalyses the synthesis of methyl anthranilate, primarily responsible for the “foxy” odour, was exclusive of the Isabel hybrid grape. Most of the proteins with different expression profiles converged into coordinated biosynthetic networks of primary metabolism, while many possible enzymes of secondary metabolism pathways, including 5-glucosyltransferases expected for hybrid grapes, remained unassigned due to incomplete protein annotation for the Vitis genus. Minor differences of protein expression distinguished V. vinifera scion grafted onto American rootstocks from purebred V. vinifera skin grapes, supporting a slight influence of the rootstock on the grape metabolism.

Quality Characteristics and Anthocyanin Profiles of Different Vitis amurensis Grape Cultivars and Hybrids from Chinese Germplasm

To evaluate the important Vitis amurensis germplasm, the quality characteristics and anthocyanin profiles of the ripe berries of 20 V. amurensis grapes and 11 interspecific hybrids in two consecutive years were analysed. Compared with the V. vinifera grapes, V. amurensis grapes had small berries with low total soluble solids and high titratable acids, and were richer in phenolic compounds except for flanan-3-ols in their skins but had lower phenolic contents in their seeds and showed lower antioxidant activities. An outstanding feature of the V. amurensis grapes was their abundant anthocyanin contents, which was 8.18-fold higher than the three wine grapes of V. vinifera. The anthocyanin composition of V. amurensis was characterized by an extremely high proportion of diglucoside anthocyanins (91.71%) and low acylated anthocyanins (0.04%). Interestingly, a new type of speculated 3,5,7-O-triglucoside anthocyanins was first identified and only detected in V. amurensis grapes and hybrids. Based on the total phenolic and anthocyanin characteristics, V. amurensis grapes were set apart from V. vinifera cultivars and the interspecific hybrids, for the same qualities, fell between them, as assessed by principal component analysis.

Characterization of 5-O-glucosyltransferase involved in anthocyanin biosynthesis in Cyclamen purpurascens

Wild cyclamen (Cyclamen purpurascens) is considered as a precious breeding material for the development of new cultivars. Malvidin 3,5-diglucoside is the main anthocyanin in the petals of C. purpurascens, whereas the F1 progeny of the C. persicum × C. purpurascens cultivars cross contains 3,5-diglucoside-type anthocyanins as the main pigment. The anthocyanin 5-O-glucosyltransferase (A5GT) enzyme is responsible for the glycosylation of the A ring of anthocyanin at the 5-O-position, which implies that the expression of A5GT is dominant in the petals of C. purpurascens × C. persicum cultivars. Here, we isolated the complete open reading frame of the A5GT gene from C. purpurascens (Cpur5GT). Results of qRT-PCR revealed that Cpur5GT shows tissue-specific expression, with strong expression in fully opened petals and weak expression in young petals. In vitro enzyme assay showed that when uridine diphosphate glucose was used as the sugar donor, recombinant Cpur5GT could catalyze the glycosylation of 3-glucoside-type anthocyanidins at the 5-O-position, but when uridine diphosphate galactose was served as glycosyl donor, the reaction could not be performed. These results demonstrate that Cpur5GT exhibits valid anthocyanin glucosylation activity and could be used to analyze the mechanism of A5GT-mediated flower coloration in cyclamen in future studies.

Flavonoid 3'-hydroxylase of Camellia nitidissima Chi. promotes the synthesis of polyphenols better than flavonoids

Camellia nitidissima Chi. is an ornamental plant of the genus Camellia L. Its flowers contain a lot of flavonoids and polyphenols. Flavonoid 3'-hydroxylase (F3'H) plays an important role in the synthesis of flavonoids, polyphenols and anthocyanins. We used PCR amplification, quantitative PCR, High-performance liquid chromatography, subcellular localization, and agrobacterium-mediated leaf disk method to study the the function of CnF3'H. The full length of CnF3'H was 1859 bp (GenBank code: HQ290518.1), with an open reading frame of 1577 bp, and encoded 518 amino acid. A phylogenetic tree analysis showed that CnF3'H was closely related to Camellia sinensis L. and C. sinensis cultivar Zhonghuang. CnF3'H was expressed in flowers, leaves, fruits, sepals, petals and stamens of C. nitidissima, and during the flowering process the expression level in flower decreased initially and then increased. CnF3'H expression was significantly positive correlated with polyphenol contents in C. nitidissima. A CnF3'H-EGFP expression vector was constructed to do the subcellular localization, we found that CnF3'H was obviously localized in the nuclear envelope and cytomembrane. In transgenic tobacco flowers, the total polyphenol content and various polyphenol constituents were significantly increased with high CnF3'H expression level, while total flavonoid contents and some flavonol constituents were increased slightly. These findings suggest that CnF3'H promotes the synthesis of polyphenols better than flavonoids.

Transcriptome analysis of genes involved in anthocyanins biosynthesis and transport in berries of black and white spine grapes (Vitis davidii)

Background

The color of berry skin is an important economic trait for grape and is essentially determined by the components and content of anthocyanins. The fruit color of Chinese wild grapes is generally black, and the profile of anthocyanins in Chinese wild grapes is significantly different from that of Vitis vinifera. However, V. davidii is the only species that possesses white berry varieties among Chinese wild grape species. Thus, we performed a transcriptomic analysis to compare the difference of transcriptional level in black and white V. davidii, in order to find some key genes that are related to anthocyanins accumulation in V. davidii.

Results

The results of anthocyanins detection revealed that 3,5-O-diglucoside anthocyanins is the predominant anthocyanins in V. davidii. It showed obvious differences from V. vinifera in the profile of the composition of anthocyanins. The transcriptome sequencing by Illumina mRNA-Seq technology generated an average of 57 million 100-base pair clean reads from each sample. Differential gene expression analysis revealed thousands of differential expression genes (DEGs) in the pairwise comparison of different fruit developmental stages between and within black and white V. davidii. After the analysis of functional category enrichment and differential expression patterns of DEGs, 46 genes were selected as the candidate genes. Some genes have been reported as being related to anthocyanins accumulation, and some genes were newly found in our study as probably being related to anthocyanins accumulation. We inferred that 3AT (VIT_03s0017g00870) played an important role in anthocyanin acylation, GST4 (VIT_04s0079g00690) and AM2 (VIT_16s0050g00910) played important roles in anthocyanins transport in V. davidii. The expression of some selected DEGs was further confirmed by quantitative real-time PCR (qRT-PCR).

Conclusions

The present study investigated the transcriptomic profiles of berry skin from black and white spine grapes at three fruit developmental stages by Illumina mRNA-Seq technology. It revealed the variety specificity of anthocyanins accumulation in V. davidi at the transcriptional level. The data reported here will provide a valuable resource for understanding anthocyanins accumulation in grapes, especially in V. davidii.

Electronic supplementary material

The online version of this article (doi:10.1186/s41065-016-0021-1) contains supplementary material, which is available to authorized users.

Recent developments in the enzymatic O-glycosylation of flavonoids

The glycosylation of bioactive compounds, such as flavonoids, is of particular relevance, as it modulates many of their pharmacokinetic parameters. This article reviews the literature between 2010 and the end of 2015 that deals with the enzymatic O-glycosylation of this class of compounds. Enzymes of glycosyltransferase family 1 remain the biocatalysts of choice for glycodiversification of flavonoids, in spite of relatively low yields. Transfers of 14 different sugars, in addition to glucose, were reported. Several Escherichia coli strains were metabolically engineered to enable a (more efficient) synthesis of the required donor during in vivo glycosylations. For the transfer of glucose, enzymes of glycoside hydrolase families 13 and 70 were successfully assayed with several flavonoids. The number of acceptor substrates and of regiospecificities characterized so far is smaller than for glycosyltransferases. However, their glycosyl donors are much cheaper and yields are considerably higher. A few success stories of enzyme engineering were reported. These improved the catalytic efficiency as well as donor, acceptor, or product ranges. Currently, the development of appropriate high-throughput screening systems appears to be the major bottleneck for this powerful technology.

Glycosylation Is a Major Regulator of Phenylpropanoid Availability and Biological Activity in Plants

The phenylpropanoid pathway in plants is responsible for the biosynthesis of a huge amount of secondary metabolites derived from phenylalanine and tyrosine. Both flavonoids and lignins are synthesized at the end of this very diverse metabolic pathway, as well as many intermediate molecules whose precise biological functions remain largely unknown. The diversity of these molecules can be further increased under the action of UDP-glycosyltransferases (UGTs) leading to the production of glycosylated hydroxycinnamates and related aldehydes, alcohols and esters. Glycosylation can change phenylpropanoid solubility, stability and toxic potential, as well as influencing compartmentalization and biological activity. (De)-glycosylation therefore represents an extremely important regulation point in phenylpropanoid homeostasis. In this article we review recent knowledge on the enzymes involved in regulating phenylpropanoid glycosylation status and availability in different subcellular compartments. We also examine the potential link between monolignol glycosylation and lignification by exploring co-expression of lignin biosynthesis genes and phenolic (de)glycosylation genes. Of the different biological roles linked with their particular chemical properties, phenylpropanoids are often correlated with the plant's stress management strategies that are also regulated by glycosylation. UGTs can for instance influence the resistance of plants during infection by microorganisms and be involved in the mechanisms related to environmental changes. The impact of flavonoid glycosylation on the color of flowers, leaves, seeds and fruits will also be discussed. Altogether this paper underlies the fact that glycosylation and deglycosylation are powerful mechanisms allowing plants to regulate phenylpropanoid localisation, availability and biological activity.