Biosynthesis and genetic regulation of proanthocyanidins in plants

Elucidating the metabolic roles of isoflavone synthase-mediated protein-protein interactions in yeast

Transient plant enzyme complexes formed via protein-protein interactions (PPIs) play crucial regulatory roles in secondary metabolism. Complexes assembled on cytochrome P450s (CYPs) are challenging to characterize metabolically due to difficulties in decoupling the PPIs' metabolic impacts from the CYPs' catalytic activities. Here, we developed a yeast-based synthetic biology approach to elucidate the metabolic roles of PPIs between a soybean-derived CYP, isoflavone synthase (GmIFS2), and other enzymes in isoflavonoid metabolism. By reconstructing multiple complex variants with an inactive GmIFS2 in yeast, we found that GmIFS2-mediated PPIs can regulate metabolic flux between two competing pathways producing deoxyisoflavonoids and isoflavonoids. Specifically, GmIFS2 can recruit chalcone synthase (GmCHS7) and chalcone reductase (GmCHR5) to enhance deoxyisoflavonoid production or GmCHS7 and chalcone isomerase (GmCHI1B1) to enhance isoflavonoid production. Additionally, we identified and characterized two novel isoflavone O-methyltransferases interacting with GmIFS2. This study highlights the potential of yeast synthetic biology for characterizing CYP-mediated complexes.

The molecular basis of flavonoid biosynthesis response to water, light, and temperature in grape berries

Flavonoids, including proanthocyanidins (PAs), anthocyanins and flavonols are essential secondary metabolites that contribute to the nutritional value and sensory quality of grape berry and red wine. Advances in molecular biology technology have led to substantial progress in understanding the regulation of flavonoid biosynthesis. The influence of terroir on grape berries and wine has garnered increasing attention, yet its comprehensive regulatory network remains underexplored. In terms of application, environmental factors such as water, light, and temperature are more easily regulated in grapevines compared to soil conditions. Therefore, we summarize their effects on flavonoid content and composition, constructing a network that links environmental factors, hormones, and metabolites to provide a deeper understanding of the underlying mechanisms. This review enriches the knowledge of the regulatory network mechanisms governing flavonoid responses to environmental factors in grapes.

Bioactive Phenylpropanoid Glycosides, Dimers, and Heterodimers from the Bark of Cinnamomum cassia (L.) J.Presl

Six new phenylpropanoid glycosides (1-6), two new phenylethanol glycosides (7 and 8), one new phenylmethanol glycoside (9), three new phenylpropanoid dimers (10-12), two new phenylpropanoid-flavan-3-ol heterodimers (13 and 14), and six known relevant compounds (15-20) were isolated and identified from the well-liked edible and medicinal substance (the bark of Cinnamomum cassia (L.) J.Presl). The structures of these isolates were determined by using spectroscopic analyses, chemical methods, and quantum chemical calculations. Notably, compounds 4-9 were rare apiuronyl-containing glycosides, and compounds 13 and 14 were heterodimers of phenylpropanoids and flavan-3-ols linked through C-9″-C-8 bonds. The antioxidant and α-glucosidase inhibitory activities of all isolates were evaluated. Compounds 10 and 12 exhibited DPPH radical scavenging capacities with IC50 values of 20.1 and 13.0 μM, respectively (vitamin C IC50 value of 14.3 μM). In the ORAC experiment, all these compounds exhibited different levels of capacity for scavenging free radicals, and compound 10 displayed extraordinary free radical scavenging capacity with the ORAC value of 6.42 ± 0.01 μM TE/μM (EGCG ORAC value of 1.54 ± 0.02 μM TE/μM). Compound 12 also showed significant α-glucosidase inhibitory activity with an IC50 of 56.3 μM (acarbose IC50 of 519.4 μM).

Identification and analysis of novel recessive alleles for Tan1 and Tan2 in sorghum

Background

The identification and analysis of allelic variation are important bases for crop diversity research, trait domestication and molecular marker development. Grain tannin content is a very important quality trait in sorghum. Higher tannin levels in sorghum grains are usually required when breeding varieties resistant to bird damage or those used for brewing liquor. Non-tannin-producing or low-tannin-producing sorghum accessions are commonly used for food and forage. Tan1 and Tan2, two important cloned genes, regulate tannin biosynthesis in sorghum, and mutations in one or two genes will result in low or no tannin content in sorghum grains. Even if sorghum accessions contain dominant Tan1 and Tan2, the tannin contents are distributed from low to high, and there must be other new alleles of the known regulatory genes or new unknown genes contributing to tannin production.

Methods

The two parents 8R306 and 8R191 did not have any known recessive alleles for Tan1 and Tan2, and it was speculated that they probably both had dominant Tan1 and Tan2 genotypes. However, the phenotypes of two parents were different; 8R306 had tannins and 8R191 had non-tannins in the grains, so these two parents were constructed as a RIL population. Bulked segregant analysis (BSA) was used to determine other new alleles of Tan1 and Tan2 or new Tannin locus. Tan1 and Tan2 full-length sequences and tannin contents were detected in wild sorghum resources, landraces and cultivars.

Results

We identified two novel recessive tan1-d and tan1-e alleles and four recessive Tan2 alleles, named as tan2-d, tan2-e, tan2-f, and tan2-g. These recessive alleles led to loss of function of Tan1 and Tan2, and low or no tannin content in sorghum grains. The loss-of-function alleles of tan1-e and tan2-e were only found in Chinese landraces, and other alleles were found in landraces and cultivars grown all around the world. tan1-a and tan1-b were detected in foreign landraces, Chinese cultivars and foreign cultivars, but not in Chinese landraces.

Conclusion

These results implied that Tan1 and Tan2 recessive alleles had different geographically distribution in the worldwide, but not all recessive alleles had been used in breeding. The discovery of these new alleles provided new germplasm resources for breeding sorghum cultivars for food and feed, and for developing molecular markers for low-tannin or non-tannin cultivar-assisted breeding in sorghum.

Combined metabolome and transcriptome analyses reveal that growing under Red shade affects secondary metabolite content in Huangjinya green tea

Shading treatments impact the tea (Camellia sinensis L.) quality. The sunlight sensitive varieties can be grown under shading nets for better growth and secondary metabolite content. Here, we studied the responses of a sunlight sensitive green tea variety "Huangjinya" by growing under colored shading nets (red, yellow, blue, and black (75% and 95%) shading rates) to find out the most suitable color of the shading net. Red shading was the most promising treatment as it positively affected the weight and length of 100 one-bud-three leaves and reduced the degree and rate of new shoots burn compared to control (natural sunlight). We then explored the comparative metabolomic changes in response to red shading by using UPLC-ESI-MS/MS system. The amino acids and derivatives, flavonoids, and alkaloids were downaccumulated whereas lipids, organic acids, and lignans were upaccumulated in Red shade grown tea samples. The red shading nets caused a decreased catechin, epicatechin, dopamine, and L-tyramine contents but increased caffeine content. We then employed transcriptome sequencing to find key changes in expressions of related genes and pathways. Notably, key genes associated with the phenylpropanoid and flavonoid biosynthesis pathways exhibited complex regulation. These expression changes suggested a potential trend of polymerization or condensation of simple molecules like catechin or pelargonidin into larger molecules like glucoside or proanthocyanidins. Here, Red shading net triggered higher expression of genes enriched in lipid biosynthesis and jasmonic acid biosynthesis, suggesting an interplay of fatty acids and JA in improving tea performance. These findings contribute to the metabolic responses of Huangjinya tea to red shading nets which might have implications for flavor and health benefits. Our data provide a foundation for further exploration and optimization of cultivation practices for this unique tea variety.

Novel allelic variations in Tannin1 and Tannin2 contribute to tannin absence in sorghum

Sorghum is an important food crop commonly used for brewing, feed, and bioenergy. Certain genotypes of sorghum contain high concentrations of condensed tannins in seeds, which are beneficial, such as protecting grains from herbivore bird pests, but also impair grain quality and digestibility. Previously, we identified Tannin1 and Tannin2, each with three recessive causal alleles, regulate tannin absence in sorghum. In this study, via characterizing 421 sorghum accessions, we further identified three novel recessive alleles from these two genes. The tan1-d allele contains a 12-bp deletion at position 659 nt and the tan1-e allele contains a 10-bp deletion at position 771 nt in Tannin1. The tan2-d allele contains a C-to-T transition, which results in a premature stop codon before the bHLH domain in Tannin2, and was predominantly selected in China. We further developed KASP assays targeting these identified recessive alleles to efficiently genotype large populations. These studies provide new insights in sorghum domestication and convenient tools for breeding programs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01463-y.

A chromosome-level genome assembly for Onobrychis viciifolia reveals gene copy number gain underlying enhanced proanthocyanidin biosynthesis

Sainfoin (Onobrychis viciifolia), which belongs to subfamily Papilionoideae of Leguminosae, is a vital perennial forage known as "holy hay" due to its high contents of crude proteins and proanthocyanidins (PAs, also called condensed tannins) that have various pharmacological properties in animal feed, such as alleviating rumen tympanic disease in ruminants. In this study, we select an autotetraploid common sainfoin (2n = 4x = 28) and report its high-quality chromosome-level genome assembly with 28 pseudochromosomes and four haplotypes (~1950.14 Mb, contig N50 = 10.91 Mb). The copy numbers of genes involved in PA biosynthesis in sainfoin are significantly greater than those in four selected Fabales species, namely, autotetraploid Medicago sativa and three other diploid species, Lotus japonicus, Medicago truncatula, and Glycine max. Furthermore, gene expansion is confirmed to be the key contributor to the increased expression of these genes and subsequent PA enhancement in sainfoin. Transcriptomic analyses reveal that the expression of genes involved in the PA biosynthesis pathway is significantly increased in the lines with high PA content compared to the lines with medium and low PA content. The sainfoin genome assembly will improve our understanding of leguminous genome evolution and biosynthesis of secondary metabolites in sainfoin.

Phenolic Profile and Bioactivity Changes of Lotus Seedpod and Litchi Pericarp Procyanidins: Effect of Probiotic Bacteria Biotransformation

Theoretically, lactic acid bacteria (LABs) could degrade polyphenols into small molecular compounds. In this study, the biotransformation of lotus seedpod and litchi pericarp procyanidins by Lactobacillus plantarum 90 (Lp90), Streptococcus thermophilus 81 (ST81), Lactobacillus rhamnosus HN001 (HN001), and Pediococcus pentosus 06 (PP06) were analysed. The growth curve results indicated that procyanidins did not significantly inhibit the proliferation of LABs. Ultra-high-performance liquid chromatography high-resolution mass spectrometry (UPLC-HRMS) revealed that procyanidin B2 and procyanidin B3 in lotus seedpod decreased by 62.85% and 25.45%, respectively, with ST81 metabolised, while kaempferol and syringetin 3-O-glucoside content increased. Although bioconversion did not increase the inhibitory function of procyanidins against glycosylation end-products in vitro, the 2,2'-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) free radical scavenging capacity and ferric reducing antioxidant power of litchi pericarp procyanidins increased by 157.34% and 6.8%, respectively, after ST81 biotransformation. These findings may inspire further studies of biological metabolism of other polyphenols and their effects on biological activity.

The regulatory role of MdNAC14-Like in anthocyanin synthesis and proanthocyanidin accumulation in red-fleshed apples

Flavonoids, such as anthocyanins and proanthocyanidins (PAs), play essential roles in plant growth, development, and stress response. Red-fleshed apples represent a valuable germplasm resource with high flavonoid content. Understanding and enriching the regulatory network controlling flavonoid synthesis in red-fleshed apples holds significant importance for cultivating high-quality fruits. In this study, we successfully isolated an NAC transcription factor, MdNAC14-Like, which exhibited a significant negative correlation with the content of anthocyanin. Transient injection of apple fruit and stable expression of callus confirmed that MdNAC14-Like acts as an inhibitor of anthocyanin synthesis. Through yeast monohybrid, electrophoretic mobility shift, and luciferase reporter assays, we demonstrated the ability of MdNAC14-Like to bind to the promoters of MdMYB9, MdMYB10, and MdUFGT, thus inhibiting their transcriptional activity and subsequently suppressing anthocyanin synthesis. Furthermore, our investigation revealed that MdNAC14-Like interacts with MdMYB12, enhancing the transcriptional activation of MdMYB12 on the downstream structural gene MdLAR, thereby promoting PA synthesis. This comprehensive functional characterization of MdNAC14-Like provides valuable insights into the intricate regulatory network governing anthocyanin and PA synthesis in apple.

Functional characterization of 2-oxoglutarate-dependent dioxygenase gene family in chickpea

Chickpea is an important leguminous crop plant with two cultivated types, desi and kabuli. It is nutritionally enriched in flavonoid content in addition to minerals and vitamins imparting huge health benefits to human beings. Our study elucidates the functionality of 2-oxoglutarate dependent dioxygenase (2-ODD) gene family members i.e., flavanone-3-hydroxylase (F3H), flavonol synthase (FLS) and anthocyanidin synthase (ANS) in chickpea using heterologous bacterial system and in-planta studies in Arabidopsis. This provides information about the biosynthesis of two very significant sub-classes of flavonoids- flavonols and anthocyanins. Here, we show that all the three homologs of F3H in chickpea can utilize not just naringenin but also eriodictyol as their substrate. Moreover, we show that FLS in chickpea exhibits bifunctionality having both FLS and F3H activity. Also, our study indicates the richness of desi chickpea over kabuli type through gene expression and metabolite content analyses. Overall, our study establishes the functionality of 2-ODD gene family involved in the early and late steps of flavonoid biosynthesis pathway in chickpea. It paves way for better genetic manipulation of the pathway for direct or indirect synthesis of three major subclasses of flavonoids (flavonol, anthocyanin and proanthocyanin) to develop nutritious, environmentally stable and healthy chickpea (Cicer arietinum) crop.

The challenge of breeding for reduced off-flavor in faba bean ingredients

The growing interest in plant protein sources, such as pulses, is driven by the necessity for sustainable food production and climate change mitigation strategies. Faba bean (Vicia faba L.) is a promising protein crop for temperate climates, owing to its remarkable yield potential (up to 8 tonnes ha-1 in favourable growing conditions) and high protein content (~29% dry matter basis). Nevertheless, the adoption of faba bean protein in plant-based products that aim to resemble animal-derived counterparts is hindered by its distinctive taste and aroma, regarded as "off-flavors". In this review, we propose to introduce off-flavor as a trait in breeding programs by identifying molecules involved in sensory perception and defining key breeding targets. We discuss the role of lipid oxidation in producing volatile and non-volatile compounds responsible for the beany aroma and bitter taste, respectively. We further investigate the contribution of saponin, tannin, and other polyphenols to bitterness and astringency. To develop faba bean varieties with diminished off-flavors, we suggest targeting genes to reduce lipid oxidation, such as lipoxygenases (lox) and fatty acid desaturases (fad), and genes involved in phenylpropanoid and saponin biosynthesis, such as zero-tannin (zt), chalcone isomerase (chi), chalcone synthase (chs), β-amyrin (bas1). Additionally, we address potential challenges, including the need for high-throughput phenotyping and possible limitations that could arise during the genetic improvement process. The breeding approach can facilitate the use of faba bean protein in plant-based food such as meat and dairy analogues more extensively, fostering a transition toward more sustainable and climate-resilient diets.

Proanthocyanidins composition in new varieties descended from Monastrell

BACKGROUND

The wine sector is constantly evolving, in order to adapt to consumer tastes. The organoleptic characteristics in wines are the main factors to obtain quality wines. Proanthocyanidins (PAs) are responsible in an important way for positive aspects in quality wines, such as body and color stability in red wines, but they are also responsible for sensory characteristics that can be negative for their quality when found in excessive concentrations. One strategy to improve grapevines and wines is to obtain new varieties, so our research institute has been selecting some of them from direct crosses between Monastrell and other considered premium varieties such as Cabernet Sauvignon and Syrah.

RESULTS

A quantitative analysis in grapes, seeds and wines was carried out during three consecutive seasons (2018, 2019 and 2020) in order to characterize PAs composition and concentration in the following new varieties: MC80 (Monastrell × Cabernet Sauvignon), MC98, MC4, MC18 and MS10 (Monastrell × Syrah). Other aspect to study was the extraction capacity of the different new varieties of PAs during maceration process into must/wine.

CONCLUSION

In general, the results showed higher concentrations in PAs in most crosses for the three seasons studied compared to Monastrell variety. It was remarkable that a higher concentration of epigallocatechin was found in most of the wines elaborated with the crosses, being a positive aspect from an organoleptic point of view, since this compound provides softness to the wines. © 2023 Society of Chemical Industry.

The synergistic ramification of insoluble dietary fiber and associated non-extractable polyphenols on gut microbial population escorting alleviation of lifestyle diseases

Most of the pertinent research which aims at exploring the therapeutic effects of polyphenols usually misapprehends a large fraction of non-extractable polyphenols due to their poor aqueous-organic solvent extractability. These polymeric polyphenols (i.e., proanthocyanins, hydrolysable tannins and phenolic acids) possess a unique property to adhere to the food matrix polysaccharides and protein sowing to their structural complexity with high glycosylation, degree of polymerization, and plenty of hydroxyl groups. Surprisingly resistance to intestinal absorption does not hinder its bioactivity but accelerates its functionality manifolds due to the colonic microbial catabolism in the gastrointestinal tract, thereby protecting the body from local and systemic inflammatory diseases. This review highlights not only the chemistry, digestion, colonic metabolism of non-extractable polyphenols (NEPP) but also summarises the synergistic effect of matrix-bound NEPP exerting local as well as systemic health benefits.

A model study on the site-specificity of (-)-epicatechin-induced reactions in β-lactoglobulin by high-resolution mass spectrometry in combination with bioinformatics

Polyphenol-protein reactions in model solutions of β-lactoglobulin (β-LG) incubated with (-)-epicatechin at 37 °C and 60 °C were monitored by microLC-timsTOF Pro-MS/MS combined with bioinformatics strategies. The addition of (-)-epicatechin to the model solutions resulted in changes in tryptic peptide profiles. Covalent bond formation between (-)-epicatechin o-quinones and β-LG was identified for the residues S27, S30, K60, C66, K69, and C160, with C160 being the predominant binding site. Furthermore, the incubation of β-LG with (-)-epicatechin significantly promoted oxidation, especially for the residues M7 and M24. The reaction of monomeric (-)-epicatechino-quinone at C160 was also identified in the milk chocolate sample. The adaptation of this study by extending the scope of the reaction products offers significant potential for comprehensive food profiling strategies.

Cocoa polyphenols and milk proteins: covalent and non-covalent interactions, chocolate process and effects on potential polyphenol bioaccesibility

In this study, we discussed covalent and non-covalent reactions between cocoa polyphenols and proteins (milk and cocoa) and the possible effects of these reactions on their bioaccessibility, considering environmental and processing conditions. Better insight into these interactions is crucial for understanding the biological effects of polyphenols, developing nutritional strategies, and improving food processing and storage. Protein-polyphenol reactions affect the properties of the final product and can lead to the formation of various precursors at various stages in the manufacturing process, such as fermentation, roasting, alkalization, and conching. Due to the complex composition of the chocolate and the various technological processes, comprehensive food profiling strategies should be applied to analyze protein-polyphenol covalent reactions covering a wide range of potential reaction products. This will help to identify potential effects on the bioaccessibility of bioactive compounds such as low-molecular-weight peptides and polyphenols. To achieve this, databases of potential reaction products and their binding sites can be generated, and the effects of various process conditions on related parameters can be investigated. This would then allow to a deeper insight into mechanisms behind protein-polyphenol interactions in chocolate, and develop strategies to optimize chocolate production for improved nutritional and sensory properties.

Oligomeric Proanthocyanidins: An Updated Review of Their Natural Sources, Synthesis, and Potentials

Oligomeric Proanthocyanidins (OPCs), as a class of compounds widely found in plants, are particularly abundant in grapes and blueberries. It is a polymer comprising many different monomers, such as catechins and epicatechins. The monomers are usually linked to each other by two types of links, A-linkages (C-O-C) and B-linkages (C-C), to form the polymers. Numerous studies have shown that compared to high polymeric procyanidins, OPCs exhibit antioxidant properties due to the presence of multiple hydroxyl groups. This review describes the molecular structure and natural source of OPCs, their general synthesis pathway in plants, their antioxidant capacity, and potential applications, especially the anti-inflammatory, anti-aging, cardiovascular disease prevention, and antineoplastic functions. Currently, OPCs have attracted much attention, being non-toxic and natural antioxidants of plant origin that scavenge free radicals from the human body. This review would provide some references for further research on the biological functions of OPCs and their application in various fields.

The complexities of proanthocyanidin biosynthesis and its regulation in plants

Proanthocyanidins (PAs) are natural flavan-3-ol polymers that contribute protection to plants under biotic and abiotic stress, benefits to human health, and bitterness and astringency to food products. They are also potential targets for carbon sequestration for climate mitigation. In recent years, from model species to commercial crops, research has moved closer to elucidating the flux control and channeling, subunit biosynthesis and polymerization, transport mechanisms, and regulatory networks involved in plant PA metabolism. This review extends the conventional understanding with recent findings that provide new insights to address lingering questions and focus strategies for manipulating PA traits in plants.

Transcriptome analysis of gall oak (Quercus infectoria): De novo assembly, functional annotation and metabolic pathways analysis

Gall oak (Quercus infectoria) is a native tree of Iran, whose gall extract is used to treat many diseases. The presence of abundant secondary metabolites with various bioactivities in this plant has made it medically important. Despite its medicinal value, due to the lack of genomic information, the biosynthetic pathways of these compounds in this species are still unknown. The current research was aimed at observing, characterizing, and investigating the biosynthetic pathways of these compounds in Q.infectoria. De novo transcriptome assembly was conducted using the RNA sequencing technique. A total of 89,335 unigenes were generated, of which 6928 unigenes showed differential expression in leaves compared to root tissue. Gene ontology examination of DEGs revealed GO-term enrichment was related to cellular processes and enzyme activity. KEGG enrichment analysis for DEGs showed that most unigenes were related to metabolic pathways and biosynthesis of secondary metabolites. Moreover, 39 families of transcription factors were identified, of which the C2H2, bZIP, bHLH, and ERF TFs had the highest frequency. In the absence of a reference genome, the overall study of transcriptome will provide a reference for future functional and comparative studies. Moreover, the data obtained from sequencing and de novo assembly can be a valuable scientific resource for Q.infectoria.

The Influence of Antioxidant Plant Extracts on the Oxidation of O/W Emulsions

The demand for natural cosmetics has steadily increased in recent years. However, challenges occur especially in quality preservation regarding oxidative spoilage of natural cosmetic products, as the use of synthetic preservatives and antioxidants is limited. Therefore, it is important to find nature-based ingredients to ensure shelf life in natural cosmetic formulations. As a result, potential is seen in the use of plant-based antioxidant extracts. The aim of this work was to determine the suitability of the method combination by measuring the antioxidant activity, oxygen concentration, and volatile oxidation products via gas chromatography (hexanal) for the characterization of the influence of some plant extracts on the oxidative stability of natural cosmetic emulsions. Plant extracts of Riesling (Vitis vinifera) pomace, apple (Malus domestica) pomace, coffee (Coffea arabica) grounds, cocoa (Theobroma cacao) husk, and coffee (Coffea arabica) powder extract were incorporated in stable O/W emulsion formulations, while an emulsion without extract functioned as blank. Afterwards, the emulsions were subjected to 3-month accelerated storage tests with and without light exposure. Their oxygen uptake was investigated, and headspace gas chromatography measurements were performed to detect the fatty acid oxidation products formed during oxidative processes in the samples. The results showed that all emulsion samples under light exposure had a higher oxygen uptake and an increase in the characteristic fatty acid oxidation products compared with those stored under light exclusion. However, differences in oxygen uptake under light exposure were observed depending on the plant extract. Therefore, for O/W emulsions, the daily oxygen consumption rate correlated exponentially with the antioxidant activity, and the hexanal concentration correlated linearly with the daily oxygen consumption rate.

Agronomic, Physicochemical, Aromatic and Sensory Characterization of Four Sweet Cherry Accessions of the Campania Region

Sweet cherries (Prunus avium L.) are greatly appreciated fruits worldwide due to their taste, color, nutritional value, and beneficial health effects. The characterization of autochthonous germplasm allows to identify genotypes that possess superior characteristics compared to standard cultivars. In this work, four accessions of sweet cherry from the Campania region (Limoncella, Mulegnana Riccia, Mulegnana Nera and Montenero) were investigated for their morpho-physiological, qualitative, aromatic, and sensorial traits in comparison with two standard cultivars (Ferrovia and Lapins). A high variability in the pomological traits resulted among the samples. Montenero showed comparable fruit weight and titratable acidity to Ferrovia and Lapins, respectively. The highest total soluble solid content was detected in Mulegnana Riccia. A considerable variability in the skin and pulp color of the cherries was observed, varying from yellow-red in Limoncella to a dark red color in Montenero. Mulegnana Nera showed the highest content of polyphenols, flavonoids, anthocyanins, and ascorbic acid compared to the standard cultivars. Volatile organic compounds profile analysis identified 34 volatile compounds, 12 of which were observed at different concentrations in all the sweet cherry genotypes while the others were genotype-dependent. Conservation and cultivation of autochthonous accessions with suitable nutritional and morpho-physiologic characteristics promotes our agrobiodiversity knowledge and allows to better plan future breeding programs.

Aglianico Grape Seed Semi-Polar Extract Exerts Anticancer Effects by Modulating MDM2 Expression and Metabolic Pathways

Grapevine (Vitis vinifera L.) seeds are rich in polyphenols including proanthocyanidins, molecules with a variety of biological effects including anticancer action. We have previously reported that the grape seed semi-polar extract of Aglianico cultivar (AGS) was able to induce apoptosis and decrease cancer properties in different mesothelioma cell lines. Concomitantly, this extract resulted in enriched oligomeric proanthocyanidins which might be involved in determining the anticancer activity. Through transcriptomic and metabolomic analyses, we investigated in detail the anticancer pathway induced by AGS. Transcriptomics analysis and functional annotation allowed the identification of the relevant causative genes involved in the apoptotic induction following AGS treatment. Subsequent biological validation strengthened the hypothesis that MDM2 could be the molecular target of AGS and that it could act in both a p53-dependent and independent manner. Finally, AGS significantly inhibited tumor progression in a xenograft mouse model of mesothelioma, confirming also in vivo that MDM2 could act as molecular player responsible for the AGS antitumor effect. Our findings indicated that AGS, exerting a pro-apoptotic effect by hindering MDM2 pathway, could represent a novel source of anticancer molecules.

Phenolic Fraction from Peanut (Arachis hypogaea L.) By-product: Innovative Extraction Techniques and New Encapsulation Trends for Its Valorization

Peanut skin is a by-product rich in bioactive compounds with high nutritional and pharmaceutical values. The phenolic fraction, rich in proanthocyanidins/procyanidins, is a relevant class of bioactive compounds, which has been increasingly applied as functional ingredients for food and pharmaceutical applications and is mostly recovered from peanut skins through low-pressure extraction methods. Therefore, the use of green high-pressure extractions is an interesting alternative to value this peanut by-product. This review addresses the benefits of the phenolic fraction recovered from peanut skin, with a focus on proanthocyanin/procyanidin compounds, and discusses the improvement of their activity, bioavailability, and protection, by methods such as encapsulation. Different applications for the proanthocyanidins, in the food and pharmaceutical industries, are also explored. Additionally, high-pressure green extraction methods, combined with micro/nanoencapsulation, using wall material derived from peanut industrial processing, may represent a promising biorefinery strategy to improve the bioavailability of proanthocyanidins recovered from underutilized peanut skins.

Oligomeric Proanthocyanidins Confer Cold Tolerance in Rice through Maintaining Energy Homeostasis

Oligomeric proanthocyanidins (OPCs) are abundant polyphenols found in foods and botanicals that benefit human health, but our understanding of the functions of OPCs in rice plants is limited, particularly under cold stress. Two rice genotypes, named Zhongzao39 (ZZ39) and its recombinant inbred line RIL82, were subjected to cold stress. More damage was caused to RIL82 by cold stress than to ZZ39 plants. Transcriptome analysis suggested that OPCs were involved in regulating cold tolerance in the two genotypes. A greater increase in OPCs content was detected in ZZ39 than in RIL82 plants under cold stress compared to their respective controls. Exogenous OPCs alleviated cold damage of rice plants by increasing antioxidant capacity. ATPase activity was higher and poly (ADP-ribose) polymerase (PARP) activity was lower under cold stress in ZZ39 than in RIL82 plants. Importantly, improvements in cold tolerance were observed in plants treated with the OPCs and 3-aminobenzamide (PARP inhibitor, 3ab) combination compared to the seedling plants treated with H₂O, OPCs, or 3ab alone. Therefore, OPCs increased ATPase activity and inhibited PARP activity to provide sufficient energy for rice seedling plants to develop antioxidant capacity against cold stress.

A recessive mutation in muscadine grapes causes berry color-loss without influencing anthocyanin pathway

Anthocyanins, a major class of flavonoids, are important pigments of grape berries. Despite the recent discovery of the genetic cause underlying the loss of color, the metabolomic and molecular responses are unknown. Anthocyanin quantification among diverse berry color muscadines suggests that all genotypes could produce adequate anthocyanin quantities, irrespective of berry color. Transcriptome profiling of contrasting color muscadine genotypes proposes a potential deficiency that occurs within the anthocyanin transport and/or degradation mechanisms and might cause unpigmented berries. Genome-wide association studies highlighted a region on chromosome-4, comprising several genes encoding glutathione S-transferases involved in anthocyanin transport. Sequence comparison among genotypes reveals the presence of two GST4b alleles that differ by substituting the conserved amino acid residue Pro₁₇₁-to-Leu. Molecular dynamics simulations demonstrate that GST4b2–Leu₁₇₁ encodes an inactive protein due to modifications within the H-binding site. Population genotyping suggests the recessive inheritance of the unpigmented trait with a GST4b2/2 homozygous. A model defining colorless muscadines’ response to the mutation stimulus, avoiding the impact of trapped anthocyanins within the cytoplasm is established.

Transcriptome profiling and mutational analysis suggest a potential deficiency in anthocyanin transport by glutathione S-transferases and/or degradation mechanisms that might cause unpigmented berries.

Function deficiency of GhOMT1 causes anthocyanidins over-accumulation and diversifies fibre colours in cotton (Gossypium hirsutum)

Naturally coloured cotton (NCC) fibres need little or no dyeing process in textile industry to low-carbon emission and are environment-friendly. Proanthocyanidins (PAs) and their derivatives were considered as the main components causing fibre coloration and made NCCs very popular and healthy, but the monotonous fibre colours greatly limit the wide application of NCCs. Here a G. hirsutum empurpled mutant (HS2) caused by T-DNA insertion is found to enhance the anthocyanidins biosynthesis and accumulate anthocyanidins in the whole plant. HPLC and LC/MS-ESI analysis confirmed the anthocyanidins methylation and peonidin, petunidin and malvidin formation are blocked. The deficiency of GhOMT1 in HS2 was associated with the activation of the anthocyanidin biosynthesis and the altered components of anthocyanidins. The transcripts of key genes in anthocyanidin biosynthesis pathway are significantly up-regulated in HS2, while transcripts of the genes for transport and decoration were at similar levels as in WT. To investigate the potential mechanism of GhOMT1 deficiency in cotton fibre coloration, HS2 mutant was crossed with NCCs. Surprisingly, offsprings of HS2 and NCCs enhanced PAs biosynthesis and increased PAs levels in their fibres from the accumulated anthocyanidins through up-regulated GhANR and GhLAR. As expected, multiple novel lines with improved fibre colours including orange red and navy blue were produced in their generations. Based on this work, a new strategy for breeding diversified NCCs was brought out by promoting PA biosynthesis. This work will help shed light on mechanisms of PA biosynthesis and bring out potential molecular breeding strategy to increase PA levels in NCCs.

Transcriptome analysis and characterization of genes associated to leaf tannin content in foxtail millet [Setaria italica (L.) P. Beauv.]

Background

Chinese chestnut is an economically important tree species whose yield and quality are seriously affected by red spider attack. Tannins is one of the most important class secondary metabolites in plants, and is closely associated with plant defense mechanisms against insect and herbivory. In our previous studies, it was revealed that several low-tannin foxtail millet varieties growing under the Chinese chestnut trees could attract red spiders to feed on their leaves and protect the chestnut trees from the infestation of red spiders, meanwhile, the growth and yield of foxtail millet plants themselves were not greatly affected.

Results

To identify genes related to leaf tannin content and selection of foxtail millet germplasm resources with low tannin content for interplanting with Chinese chestnut and preventing the red spider attack, the leaves of 4 varieties with different levels of tannin content were harvested for comparative transcriptome analysis. In total, 335 differentially expressed genes (DEGs) were identified. For acquisition of gene functions and biological pathways they involved in, gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment analyses were performed, and several DEGs were found to possibly participate in the tannins biosynthesis pathway and transport processes of precursors. In addition, according to the PlantTFDB database, some transcription factors were predicted among the DEGs, suggesting their role in regulation of tannins biosynthesis pathway.

Conclusion

Our results provide valuable gene resources for understanding the biosynthesis and regulation mechanisms of tannins in foxtail millet, and pave the way for speeding up the breeding of low-tannin varieties through marker-assisted selection, which could be utilized for interplanting with Chinese chestnut trees to confer protection against red spider attack.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08746-8.

Rapid fingerprinting of extractable and non-extractable polyphenols from tropical fruit peels using direct analysis in real time coupled to orbitrap mass spectrometry

A simple and rapid direct analysis in real-time coupled to high-resolution mass spectrometry (DART-HRMS) methodology was developed to generate the extractable and non-extractable polyphenols (NEPs) fingerprint for four different passion fruits, G. mangostana, and A. squamosa peels as case-study to investigate the influence of alkaline hydrolysis and enzymatic-assisted extraction (EAE) on the recovery of NEPs. The extraction residue obtained after these treatments was also analyzed by DART-HRMS. Data compiled from DART-HRMS mass spectra were processed with principal component analysis to discriminate among the different treatments. EAE with Depol enzyme enabled to obtain NEPs with the highest signal intensity in DART-HRMS analysis from all peels except for P. edulis and A. squamosa peels. In these two cases, NEPs were better extracted by EAE with Promod enzyme and alkaline hydrolysis. Results showed that the applied treatments were efficient to extract NEPs since their signal intensities in the extraction residues were very low compared with their extracts.

Strategies of tolerance reflected in two North American maple genomes

The first chromosome‐scale assemblies for North American members of the Acer genus, sugar maple (Acer saccharum) and boxelder (Acer negundo), as well as transcriptomic evaluation of the abiotic stress response in A. saccharum are reported. This integrated study describes in‐depth aspects contributing to each species' approach to tolerance and applies current knowledge in many areas of plant genome biology with Acer physiology to help convey the genomic complexities underlying tolerance in broadleaf tree species.

Phenolic profiles and their responses to pre- and post-harvest factors in small fruits: a review

The consumption of small fruits has increased in recent years. Besides their appealing flavor, the commercial success of small fruits has been partially attributed to their high contents of phenolic compounds with multiple health benefits. The phenolic profiles and contents in small fruits vary based on the genetic background, climate, growing conditions, and post-harvest handling techniques. In this review, we critically compare the profiles and contents of phenolics such as anthocyanins, flavonols, flavan-3-ols, and phenolic acids that have been reported in bilberries, blackberries, blueberries, cranberries, black and red currants, raspberries, and strawberries during fruit development and post-harvest storage. This review offers researchers and breeders a general guideline for the improvement of phenolic composition in small fruits while considering the critical factors that affect berry phenolics from cultivation to harvest and to final consumption.

Exogenous proanthocyanidins improve tolerance of Cu-toxicity by amelioration of oxidative damage and re-programming of gene expression in Medicago sativa

Excess copper (Cu) in soil due to industrial and agricultural practices can result in reduced plant growth. Excess Cu resulted in severely retarded root growth with severe discoloration of Alfalfa (Medicago sativa) and Medicago truncatula. Growth in the presence of hydrogen peroxide resulted in similar symptoms that could be partially recovered by the addition of the reductant ascorbic acid revealing damage was likely due to oxidative stress. The addition of proanthocyanidins (PAs) in the presence of Cu prevented much of the damage, including plant growth and restoration of lignin synthesis which was inhibited in the presence of excess Cu. Transcriptome analyses of the impact of excess Cu and the amelioration after PAs treatment revealed that changes were enriched in functions associated with the cell wall and extracellular processes, indicating that inhibition of cell wall synthesis was likely the reason for retarded growth. Excess Cu appeared to induce a strong defense response, along with alterations in the expression of a number of genes encoding transcription factors, notably related to ethylene signaling. The addition of PAs greatly reduced this response, and also induced novel genes that likely help ameliorate the effects of excess Cu. These included induction of genes involved in the last step of ascorbic acid biosynthesis and of enzymes involved in cell wall synthesis. Combined, these results show that excess Cu causes severe oxidative stress damage and inhibition of cell wall synthesis, which can be relieved by the addition of PAs.

Composition Changes in Lycium ruthenicum Fruit Dried by Different Methods

The fruit of Lycium ruthenicum (LRF), known as black wolfberry, is a medicinal and edible fruit. The fresh LRF is perishable and has only about 3 days of shelf life. Drying could prolong the shelf life of LRF. However, it could imply physical changes and chemical modification. This study evaluated the effect of sun drying (SD), hot air drying (HD), and freeze drying (FD) on the appearance characteristics, moisture content, bioactive compounds, amino acid composition, and antioxidant activity of LRF. The results showed that LRF dried by FD was round, expansive, fragile, and maintained the largest amount of appearance traits among the three drying methods. Drying methods had a significant effect on phytochemical content and antioxidant activity of LRF (P < 0.05). Principal component analysis (PCA) showed that procyanidin content (PAC), asparagine (Asn), total phenolic content (TPC), total anthocyanin content (TAC), and moisture content were the main sources of the difference in LRF dried by different methods. The characteristic of LRF in FD was low moisture content, and high TPC, Asn, PAC, and TAC. Sun drying was opposite to FD. Hot air drying was high TPC and low TAC content. The quality of LRF was in the order of FD > HD > SD based on comprehensive evaluation of the phytochemical component content and antioxidant capacity. Additionally, the water temperature and soaking time had different antioxidant activity effect on LRF dried by different methods. These findings will provide useful information for production and utilization of LRF.

Review of the recent developments in metabolomics-based phytochemical research

Phytochemicals are important bioactive components present in natural products. Although the health benefits of many food products are well-known and accepted as a common knowledge, the identity of the main bioactive molecules and the mechanism by which they interact in the body of human are often unknown. It was only in the last 30 years when the field of metabolomics had matured that the identification of such molecules with bioactivity has been made possible through the development of instruments to separate and computational techniques to characterize complex samples. This in turn has enabled in vitro studies to quantify the biological activity of the respective phytochemical either in mice models or in humans. In this review, the importance of key dietary phytochemicals such as phenolic acids, flavonoids, carotenoids, resveratrol, curcumin, and capsaicinoids are discussed together with their potential functions for human health. Untargeted metabolomics, in particular, liquid chromatography mass spectrometry, is the most used method to isolate, identify and profile bioactive compounds in the study of phytochemicals in foods. The application of metabolomics in drug discovery is a common practice nowadays and has boosted the drug and/or supplement manufacturing sector.HighlightsPhytochemicals are beneficial compounds for human healthPhytochemicals are plant-based bioactive and obtainable from natural productsUntargeted metabolomics has boosted the discovery of phytochemicals from foodTargeted metabolomics is key in the authentication and screening of phytochemicalsMetabolomics of phytochemicals is reshaping the road to drug and supplement manufacture.

Proanthocyanidins and Where to Find Them: A Meta-Analytic Approach to Investigate Their Chemistry, Biosynthesis, Distribution, and Effect on Human Health

Proanthocyanidins (PACs) are a class of polyphenolic compounds that are attracting considerable interest in the nutraceutical field due to their potential health benefits. However, knowledge about the chemistry, biosynthesis, and distribution of PACs is limited. This review summarizes the main chemical characteristics and biosynthetic pathways and the main analytical methods aimed at their identification and quantification in raw plant matrices. Furthermore, meta-analytic approaches were used to identify the main plant sources in which PACs were contained and to investigate their potential effect on human health. In particular, a cluster analysis identified PACs in 35 different plant families and 60 different plant parts normally consumed in the human diet. On the other hand, a literature search, coupled with forest plot analyses, highlighted how PACs can be actively involved in both local and systemic effects. Finally, the potential mechanisms of action through which PACs may impact human health were investigated, focusing on their systemic hypoglycemic and lipid-lowering effects and their local anti-inflammatory actions on the intestinal epithelium. Overall, this review may be considered a complete report in which chemical, biosynthetic, ecological, and pharmacological aspects of PACs are discussed.

CRISPR-Act3.0 for highly efficient multiplexed gene activation in plants

RNA-guided CRISPR activation (CRISPRa) systems have been developed in plants. However, the simultaneous activation of multiple genes remains challenging. Here, we develop a highly robust CRISPRa system working in rice, Arabidopsis and tomato, CRISPR-Act3.0, through systematically exploring different effector recruitment strategies and various transcription activators based on deactivated Streptococcus pyogenes Cas9 (dSpCas9). The CRISPR-Act3.0 system results in fourfold to sixfold higher activation than the state-of-the-art CRISPRa systems. We further develop a tRNA-gR2.0 (single guide RNA 2.0) expression system enabling CRISPR-Act3.0-based robust activation of up to seven genes for metabolic engineering in rice. In addition, CRISPR-Act3.0 allows the simultaneous modification of multiple traits in Arabidopsis, which are stably transmitted to the T3 generations. On the basis of CRISPR-Act3.0, we elucidate guide RNA targeting rules for effective transcriptional activation. To target T-rich protospacer adjacent motifs (PAMs), we transfer this activation strategy to CRISPR-dCas12b and further improve the dAaCas12b-based CRISPRa system. Moreover, we develop a potent near-PAM-less CRISPR-Act3.0 system on the basis of the SpRY dCas9 variant, which outperforms the dCas9-NG system in both activation potency and targeting scope. Altogether, our study has substantially improved the CRISPRa technology in plants and provided plant researchers a powerful toolbox for efficient gene activation in foundational and translational research.

The Sorghum Grain Mold Disease Complex: Pathogens, Host Responses, and the Bioactive Metabolites at Play

Grain mold is a major concern in sorghum [Sorghum bicolor (L.) Moench] production systems, threatening grain quality, safety, and nutritional value as both human food and livestock feed. The crop's nutritional value, environmental resilience, and economic promise poise sorghum for increased acreage, especially in light of the growing pressures of climate change on global food systems. In order to fully take advantage of this potential, sorghum improvement efforts and production systems must be proactive in managing the sorghum grain mold disease complex, which not only jeopardizes agricultural productivity and profitability, but is also the culprit of harmful mycotoxins that warrant substantial public health concern. The robust scholarly literature from the 1980s to the early 2000s yielded valuable insights and key comprehensive reviews of the grain mold disease complex. Nevertheless, there remains a substantial gap in understanding the complex multi-organismal dynamics that underpin the plant-pathogen interactions involved - a gap that must be filled in order to deliver improved germplasm that is not only capable of withstanding the pressures of climate change, but also wields robust resistance to disease and mycotoxin accumulation. The present review seeks to provide an updated perspective of the sorghum grain mold disease complex, bolstered by recent advances in the understanding of the genetic and the biochemical interactions among the fungal pathogens, their corresponding mycotoxins, and the sorghum host. Critical components of the sorghum grain mold disease complex are summarized in narrative format to consolidate a collection of important concepts: (1) the current state of sorghum grain mold in research and production systems; (2) overview of the individual pathogens that contribute to the grain mold complex; (3) the mycotoxin-producing potential of these pathogens on sorghum and other substrates; and (4) a systems biology approach to the understanding of host responses.

The Interactions between Polyphenols and Microorganisms, Especially Gut Microbiota

This review presents the comprehensive knowledge about the bidirectional relationship between polyphenols and the gut microbiome. The first part is related to polyphenols' impacts on various microorganisms, especially bacteria, and their influence on intestinal pathogens. The research data on the mechanisms of polyphenol action were collected together and organized. The impact of various polyphenols groups on intestinal bacteria both on the whole "microbiota" and on particular species, including probiotics, are presented. Moreover, the impact of polyphenols present in food (bound to the matrix) was compared with the purified polyphenols (such as in dietary supplements) as well as polyphenols in the form of derivatives (such as glycosides) with those in the form of aglycones. The second part of the paper discusses in detail the mechanisms (pathways) and the role of bacterial biotransformation of the most important groups of polyphenols, including the production of bioactive metabolites with a significant impact on the human organism (both positive and negative).

Responses of Lotus corniculatus to environmental change 3: The sensitivity of phenolic accumulation to growth temperature and light intensity and effects on tissue digestibility

Growth temperature and light intensity are major drivers of phenolic accumulation in Lotus corniculatus resulting in major changes in carbon partitioning which significantly affects tissue digestibility and forage quality. The response of plant growth, phenolic accumulation and tissue digestibility to light and temperature was determined in clonal plants of three genotypes of Lotus corniculatus (birdsfoot trefoil) cv Leo, with low, intermediate or high levels of proanthocyanidins (condensed tannins). Plants were grown from 10 °C to 30 °C, or at light intensities from 20 to 500 µm m^-2 s^-1. Plants grown at 25 °C had the highest growth rate and highest digestibility, whereas the maximum tannin concentration was found in plants grown at 15 °C. Approximately linear increases in leaf flavonol glycoside levels were found with increasing growth temperature in the low tannin genotype. Tannin hydroxylation increased with increasing growth temperature but decreased with increasing light intensity. The major leaf flavonols were kaempferol glycosides of which kaempferol-3-glucoside and kaempferol-3,7-dirhamnoside were the major components. Increases in both tannin and total flavonol concentrations in leaves were linearly related to light intensity and were preceded by a specific increase in the transcript level of a non-legume type chalcone isomerase. Changes in growth temperature and light intensity, therefore, result in major changes in the partitioning of carbon into phenolics, which significantly affects tissue digestibility and nutritional quality with a high correlation between tannin concentration and leaf digestibility.

Yield and compositions of bark phenolic extractives from three commercially significant softwoods show intra- and inter-specific variation

Tree bark is rich in commercially valuable secondary metabolites such as polyphenolic compounds like flavonoids and tannins. The yield and composition of bark extractives from Abies alba varies longitudinally within the stem. A. alba bark above the crown had the greatest extractive content, but the concentration of polyphenolic compounds was greatest below the crown. Here, we use a nonlinear model describing how bark extractive yields of A. alba, Picea abies and Pseudotsuga menziesii change with height, where differences among species are accounted for using different model coefficients. For all species there is longitudinal variability in extract yield. For P. abies and P. menziesii, the form of that variation differs depending on whether the bark was located at the same position in the stem as branches. Although the relationship form of total extractive yield differs between branched and un-branched samples, the relationship forms for individual compound yields does not change depending on branch presence. Despite trees from thinned stands having longer crowns and faster growth rates, indicative of greater photosynthetic activity, there was no evidence that thinning had affected either the yield or composition of extractives in these species. In P. abies, the proportions of flavonoids was higher in bark from the top of the tree, whereas epi-gallocatechin gallate was found in high proportions at the stem base. In P. menziesii bark extracts, taxifolin was the dominant compound, present in significantly higher proportions in bark towards the base of the stem.

The Effect of Light Intensity on the Expression of Leucoanthocyanidin Reductase in Grapevine Calluses and Analysis of Its Promoter Activity

To investigate the effect of light intensity on flavonoid biosynthesis, grapevine calluses were subjected to high light (HL, 250 μmol m⁻² s⁻¹) and dark (0 μmol m⁻² s⁻¹) in comparison to 125 μmol m⁻² s⁻¹ under controlled conditions (NL). The alteration of flavonoid profiles was determined and was integrated with RNA sequencing (RNA-seq)-based transcriptional changes of the flavonoid pathway genes. Results revealed that dark conditions inhibited flavonoid biosynthesis. Increasing light intensity affected flavonoids differently—the concentrations of flavonols and anthocyanins as well as the expressions of corresponding genes were less affected, whereas flavan-3-ol concentrations were predominantly increased, which caused enhanced trans-flavan-3-ol concentrations. Moreover, genes encoding leucoanthocyanidin reductase (LAR) exhibited different response patterns to light intensity changes—VviLAR1 expression increased with an increased light intensity, whereas VviLAR2 expression was insensitive. We further confirmed that the known transcription factors (TFs) involved in regulating flavan-3-ol biosynthesis utilized VviLAR1 as a target gene in grapevine calluses. In addition, VviLAR1 promoter activity was more sensitive to light intensity changes than that of VviLAR2 as determined using a transgenic Arabidopsis leaf system. These results suggested that light intensity had the most prominent effect on trans-flavan-3-ols in grapevine calluses and demonstrated that the two LAR genes had different response patterns to light intensity changes.

Transcriptomic Analysis of Root Restriction Effects on Phenolic Metabolites during Grape Berry Development and Ripening

In the present study, the effects of root restriction (RR) on the main phenolic metabolites and the related gene expression at different developmental stages were studied at the transcriptomic and metabolomic levels in "Summer Black" grape berries (Vitis vinifera × Vitis labrusca). The results were as follows: seven phenolic acid compounds, three stilbene compounds, nine flavonol compounds, 10 anthocyanin compounds, and 24 proanthocyanidin compounds were identified by ultra-performance liquid chromatography-high-resolution mass spectrometry. RR treatment significantly promoted the biosynthesis of phenolic acid, trans-resveratrol, flavonol, and anthocyanin and also affected the proanthocyanidin content, which was elevated in the early developmental stages and then reduced in the late developmental stages. The functional genes for phenylalanine ammonia-lyase, trans-cinnamate 4-monooxygenase, 4-coumarate-CoA ligase, shikimate O-hydroxycinnamoyl transferase, chalcone synthase, chalcone isomerase, stilbene synthase, flavonoid 3',5'-hydroxylase, anthocyanidin 3-O-glucosyltransferase, and the transcription factors MYBA1, MYBA2, MYBA3, and MYBA22 were inferred to play critical roles in the changes regulated by RR treatment.

Synthesis of A-Type Proanthocyanidins and Their Analogues: A Comprehensive Review

Proanthocyanidins (PACs) are oligomers or polymers composed of units of flavanols. A-type PACs are a subclass of PACs characterized by the presence of at least a double linkage between two consecutive monomers of flavanol. These A-type PACs are found in some fruits and spices and possess potential health benefits as a result of their interesting biological activities, and consequently, their isolation and synthesis have given rise to great interest in the past. This review summarizes the synthetic efforts made to obtain both naturally occurring A-type PACs and their structurally simplified analogues. Most of the synthetic protocols reported involve the addition of a π-nucleophilic molecule over a molecule with two electrophilic carbons, such as a chalcone, a flavylium salt, or a flavanol derivative, among others. Synthesis of A-type PACs remains an issue at a very early stage of development compared to that of PACs with single linkages between monomers (B-type PACs), but the advances that are taking place in the last few years point to a significant development of the subject in the near future.

Do Faba Bean Genotypes Carrying Different Zero-Tannin Genes (zt1 and zt2) Differ in Phenolic Profiles?

Faba bean is a cool season grain legume that produces seeds with a high protein content. Seed coat tannins limit its use in food and feed. A low-tannin phenotype is controlled by either of two unlinked recessive genes zt1 and zt2. Liquid chromatography-mass spectrometry was used to characterize phenolic profiles of seed coat and flower tissue of three faba bean genotypes: CDC Snowdrop (zt1 gene), Disco/2 (zt2 gene), and ILB 938/2 (tannin-containing). For both tissues, clear differences in phenolic profiles of ILB 938/2 were observed in comparison to both low-tannin lines. Although seed coat phenolic profiles of zt1 and zt2 genotypes were similar, distinct differences were evident in flower tissue, suggesting that the gene action results in some different end products of the phenolic biosynthetic pathway. These distinctive compounds could be used as biochemical markers to distinguish between low-tannin phenotypes.

Localization of Flavan-3-ol Species in Peanut Testa by Mass Spectrometry Imaging

Flavan-3-ols, procyanidins and their monomers are major flavonoids present in peanuts that show a wide range of biological properties and health benefits, based on their potent antioxidant activity. Procyanidin oligomers, especially A-type, are reportedly abundant in peanut skin; however, their localization in the raw peanut testa remains poorly understood. Therefore, we performed matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) to investigate the localization of flavan-3-ols in peanut testa. 1,5-Diaminonaphthalene was coated onto the peanut section by matrix vapor deposition/recrystallization, and MALDI-MSI measurements were performed in the negative-ion mode. Peaks matching the m/z values of flavan-3-ol [M - H]^- ions were observed in the mass spectrum extracted from the outer epidermis of the peanut testa, using the region of interest function. Catechin and/or epicatechin, five A-type, and one B-type procyanidins were assigned by the fragment ions generated by retro-Diels-Alder, heterocyclic ring fission, and quinone methide reactions detected in MALDI-tandem MS spectra. These flavan-3-ols were localized in the outer epidermis of the peanut testa. This information will contribute to improving the extraction and purification efficiencies of flavan-3-ols from peanut testa. As flavan-3-ols display anti-microbial activity, it is speculated that flavan-3-ols present in the outer epidermis of peanut testa act to prevent pathogen infection.

Evaluating the influence of temperature on proanthocyanidin biosynthesis in developing grape berries (Vitis vinifera L.)

The variability in grape (Vitis vinifera L.) proanthocyanidin content is largely attributable to viticultural and environmental conditions. However, the particular effect temperature has on proanthocyanidin biosynthesis is poorly understood. The aim of the present study was to ascertain the magnitude of the effect of temperature on proanthocyanidin biosynthesis in Cabernet Sauvignon grape berries cultured in vitro. In addition, the effects of temperature on global gene transcription were evaluated, and the microarray data were later validated by quantitative real-time PCR (qPCR). The grape berries used in this research were sampled 3-4 weeks after full bloom and cultured in vitro either under a low (20 °C) or high (30 °C) temperature treatment for 15 days (d) with sampling occurring every five days. The proanthocyanidin content was higher in the skin and seeds of grape berries cultured at a low temperature compared with a high temperature. However, overall proanthocyanidin composition between the treatments was not significantly affected. Microarray data revealed a total of 1298 genes with ≥ 3.5-fold expression differences under high temperature conditions. High temperature also inhibited the expression level of key genes involved in proanthocyanidin biosynthesis, anthocyanidin reductase (ANR) and leucoanthocyanidin reductase-1 (LAR-1) within the berry skin. However, the transcriptomic accumulation of transcription factors, such as VvMybPAs, VvMyb5a and VvMyb5b, was barely influenced during the peak expression of ANR and LAR-1. Thus, the present study revealed that temperature has a significant effect on proanthocyanidin biosynthesis in grape during berry development through enhancing the expression of key biosynthetic genes.

High-Performance Liquid Chromatography-Hydrogen/Deuterium Exchange-High-Resolution Mass Spectrometry Partial Identification of a Series of Tetra- and Pentameric Cyclic Procyanidins and Prodelphinidins in Wine Extracts

A solid-phase extraction method was applied for the identification of a series of unconventional crown (macrocyclic) B-type proanthocyanidin tetramers (m/z 1169.2557, 1185.2507, 1201.2456, and 1217.2405) and pentamers (m/z 1457.3191, 1473.3140, 1489.3090, 1505.3039, and 1521.2988) containing (epi)catechins only (procyanidins) or (epi)catechins and (epi)gallocatechins (prodelphinidins). These compounds were identified in red wine by high-performance liquid chromatography-high-resolution mass spectrometry coupled with online hydrogen/deuterium exchange (HDX) after purification with a C18 solid-phase extraction phase from the original wine sample. The number and type of monomer units present in each procyanidin and prodelphinidin are discussed on the basis of the experimental measured masses, their retention time distribution among observed isomers, tandem mass spectrometry fragmentations, and the HDX-induced shift of the theoretical monoisotopic mass. The elution in reverse-phase high-performance liquid chromatography shifted to lower retention times when the ratio of (epi)gallocatechin units in these molecules increased with respect to the content of (epi)catechin units, as a consequence of the increase of polarity.