Characterization of Brassica napus Flavonol Synthase Involved in Flavonol Biosynthesis in Brassica napus L

Safflower CtFLS1-Induced Drought Tolerance by Stimulating the Accumulation of Flavonols and Anthocyanins in Arabidopsis thaliana

Flavonol synthase gene (FLS) is a member of the 2-oxoglutarate-dependent dioxygenase (2-ODD) superfamily and plays an important role in plant flavonoids biosynthetic pathways. Safflower (Carthamus tinctorius L.), a key source of traditional Chinese medicine, is widely cultivated in China. Although the flavonoid biosynthetic pathway has been studied in several model species, it still remains to be explored in safflower. In this study, we aimed to elucidate the role of CtFLS1 gene in flavonoid biosynthesis and drought stress responses. The bioinformatics analysis on the CtFLS1 gene showed that it contains two FLS-specific motifs (PxxxIRxxxEQP and SxxTxLVP), suggesting its independent evolution. Further, the expression level of CtFLS1 in safflower showed a positive correlation with the accumulation level of total flavonoid content in four different flowering stages. In addition, CtFLS1-overexpression (OE) Arabidopsis plants significantly induced the expression levels of key genes involved in flavonol pathway. On the contrary, the expression of anthocyanin pathway-related genes and MYB transcription factors showed down-regulation. Furthermore, CtFLS1-OE plants promoted seed germination, as well as resistance to osmotic pressure and drought, and reduced sensitivity to ABA compared to mutant and wild-type plants. Moreover, CtFLS1 and CtANS1 were both subcellularly located at the cell membrane and nucleus; the yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assay showed that they interacted with each other at the cell membrane. Altogether, these findings suggest the positive role of CtFLS1 in alleviating drought stress by stimulating flavonols and anthocyanin accumulation in safflower.

An LcMYB111-LcHY5 Module Differentially Activates an LcFLS Promoter in Different Litchi Cultivars

Flavonol synthase (FLS) is the crucial enzyme of the flavonol biosynthetic pathways, and its expression is tightly regulated in plants. In our previous study, two alleles of LcFLS,LcFLS-A and LcFLS-B, have been identified in litchi, with extremely early-maturing (EEM) cultivars only harboring LcFLS-A, while middle-to-late-maturing (MLM) cultivars only harbor LcFLS-B. Here, we overexpressed both LcFLS alleles in tobacco, and transgenic tobacco produced lighter-pink flowers and showed increased flavonol levels while it decreased anthocyanin levels compared to WT. Two allelic promoters of LcFLS were identified, with EEM cultivars only harboring proLcFLS-A, while MLM cultivars only harbor proLcFLS-B. One positive and three negative R2R3-MYB transcription regulators of LcFLS expression were identified, among which only positive regulator LcMYB111 showed a consistent expression pattern with LcFLS, which both have higher expression in EEM than that of MLM cultivars. LcMYB111 were further confirmed to specifically activate proLcFLS-A with MYB-binding element (MBE) while being unable to activate proLcFLS-B with mutated MBE (MBEm). LcHY5 were also identified and can interact with LcMYB111 to promote LcFLS expression. Our study elucidates the function of LcFLS and its differential regulation in different litchi cultivars for the first time.

GbFLSa overexpression negatively regulates proanthocyanin biosynthesis

Flavonoids are important secondary metabolites with extensive pharmacological functions. Ginkgo biloba L. (ginkgo) has attracted extensive attention because of its high flavonoid medicinal value. However, little is understood about ginkgo flavonol biosynthesis. Herein, we cloned the full-length gingko GbFLSa gene (1314 bp), which encodes a 363 amino acid protein that has a typical 2-oxoglutarate (2OG)-Fe(II) oxygenase region. Recombinant GbFLSa protein with a molecular mass of 41 kDa was expressed in Escherichia coli BL21(DE3). The protein was localized to the cytoplasm. Moreover, proanthocyanins, including catechin, epicatechin, epigallocatechin and gallocatechin, were significantly less abundant in transgenic poplar than in nontransgenic (CK) plants. In addition, dihydroflavonol 4-reductase, anthocyanidin synthase and leucoanthocyanidin reductase expression levels were significantly lower than those of their CK counterparts. GbFLSa thus encodes a functional protein that might negatively regulate proanthocyanin biosynthesis. This study helps elucidate the role of GbFLSa in plant metabolism and the potential molecular mechanism of flavonoid biosynthesis.

The Flavonoid Biosynthesis and Regulation in Brassica napus: A Review

Brassica napus is an important crop for edible oil, vegetables, biofuel, and animal food. It is also an ornamental crop for its various petal colors. Flavonoids are a group of secondary metabolites with antioxidant activities and medicinal values, and are important to plant pigmentation, disease resistance, and abiotic stress responses. The yellow seed coat, purple leaf and inflorescence, and colorful petals of B. napus have been bred for improved nutritional value, tourism and city ornamentation. The putative loci and genes regulating flavonoid biosynthesis in B. napus have been identified using germplasms with various seed, petal, leaf, and stem colors, or different flavonoid contents under stress conditions. This review introduces the advances of flavonoid profiling, biosynthesis, and regulation during development and stress responses of B. napus, and hopes to help with the breeding of B. napus with better quality, ornamental value, and stress resistances.

Transcriptomic Analysis Provides Insight into the ROS Scavenging System and Regulatory Mechanisms in Atriplex canescens Response to Salinity

Atriplex canescens is a representative halophyte with excellent tolerance to salt. Previous studies have revealed certain physiological mechanisms and detected functional genes associated with salt tolerance. However, knowledge on the ROS scavenging system and regulatory mechanisms in this species when adapting to salinity is limited. Therefore, this study further analyzed the transcriptional changes in genes related to the ROS scavenging system and important regulatory mechanisms in A. canescens under saline conditions using our previous RNA sequencing data. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation revealed that the differentially expressed genes (DEGs) were highly enriched in signal transduction- and reactive oxygen species-related biological processes, including "response to oxidative stress", "oxidoreductase activity", "protein kinase activity", "transcription factor activity", and "plant hormone signal transduction". Further analyses suggested that the transcription abundance of many genes involved in SOD, the AsA-GSH cycle, the GPX pathway, PrxR/Trx, and the flavonoid biosynthesis pathway were obviously enhanced. These pathways are favorable for scavenging excessive ROS induced by salt and maintaining the integrity of the cell membrane. Meanwhile, many vital transcription factor genes (WRKY, MYB, ZF, HSF, DREB, and NAC) exhibited increased transcripts, which is conducive to dealing with saline conditions by regulating downstream salt-responsive genes. Furthermore, a larger number of genes encoding protein kinases (RLK, CDPK, MAPK, and CTR1) were significantly induced by saline conditions, which is beneficial to the reception/transduction of salt-related signals. This study describes the abundant genetic resources for enhancing the salt tolerance in salt-sensitive plants, especially in forages and crops.

An R3-MYB repressor, BnCPC forms a feedback regulation with MBW complex to modulate anthocyanin biosynthesis in Brassica napus

BACKGROUND

Anthocyanins are metabolites of phenylpropanoid pathway, and involves in diverse processes of plant development and adaptation, which are regulated by the MYB-bHLH-WD40 (MBW) protein complexes. Many R2R3-MYB activators have been well characterized, but the MYB repressors in anthocyanin biosynthesis were recognized recently, which are also important in modulating phenylpropanoid metabolism in plants. The regulatory mechanism of anthocyanin biosynthesis in oil crop Brassica napus remains to be revealed.

RESULTS

In this study, we identified an anthocyanin repressor BnCPC in B. napus. BnCPC encoded a typical R3-MYB protein containing a conserved [D/E]Lx2[R/K]x3Lx6Lx3R motif for interaction with bHLH proteins. Overexpression of BnCPC in B. napus inhibited anthocyanin accumulation, especially under anthocyanin inducible conditions. Protein-protein interaction and dual-luciferase assays confirmed that BnCPC could compete with BnPAP1 to interact with bHLHs (BnTT8 and BnEGL3), and repress the expression of anthocyanin biosynthetic genes (e.g., BnDFR) that activated by MBW complexes. Moreover, we found BnCPC inhibited the MBW complex-induced BnCPC activity.

CONCLUSIONS

Overall, this research demonstrated that BnCPC repressed anthocyanin biosynthesis by affecting the formation of MBW complex, and formed a feedback loop to regulate anthocyanin accumulation in B. napus.

Genome-wide identification of key enzyme-encoding genes and the catalytic roles of two 2-oxoglutarate-dependent dioxygenase involved in flavonoid biosynthesis in Cannabis sativa L

Background

Flavonoids are necessary for plant growth and resistance to adversity and stress. They are also an essential nutrient for human diet and health. Among the metabolites produced in Cannabis sativa (C. sativa), phytocannabinoids have undergone extensive research on their structures, biosynthesis, and biological activities. Besides the phytocannabinoids, C. sativa is also rich in terpenes, alkaloids, and flavonoids, although little research has been conducted in this area.

Results

In this study, we identified 11 classes of key enzyme-encoding genes, including 56 members involved in the flavonoid biosynthesis in C. sativa, from their physical characteristics to their expression patterns. We screened the potentially step-by-step enzymes catalyzing the precursor phenylalanine to the end flavonoids using a conjoin analysis of gene expression with metabolomics from different tissues and chemovars. Flavonol synthase (FLS), belonging to the 2-oxoglutarate-dependent dioxygenase (2-ODD) superfamily, catalyzes the dihydroflavonols to flavonols. In vitro recombinant protein activity analysis revealed that CsFLS2 and CsFLS3 had a dual function in converting naringenin (Nar) to dihydrokaempferol (DHK), as well as dihydroflavonols to flavonols with different substrate preferences. Meanwhile, we found that CsFLS2 produced apigenin (Api) in addition to DHK and kaempferol when Nar was used as the substrate, indicating that CsFLS2 has an evolutionary relationship with Cannabis flavone synthase I.

Conclusions

Our study identified key enzyme-encoding genes involved in the biosynthesis of flavonoids in C. sativa and highlighted the key CsFLS genes that generate flavonols and their diversified functions in C. sativa flavonoid production. This study paves the way for reconstructing the entire pathway for C. sativa’s flavonols and cannflavins production in heterologous systems or plant culture, and provides a theoretical foundation for discovering new cannabis-specific flavonoids.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01933-y.

Non-target molecular network and putative genes of flavonoid biosynthesis in Erythrina velutina Willd., a Brazilian semiarid native woody plant

Erythrina velutina is a Brazilian native tree of the Caatinga (a unique semiarid biome). It is widely used in traditional medicine showing anti-inflammatory and central nervous system modulating activities. The species is a rich source of specialized metabolites, mostly alkaloids and flavonoids. To date, genomic information, biosynthesis, and regulation of flavonoids remain unknown in this woody plant. As part of a larger ongoing research goal to better understand specialized metabolism in plants inhabiting the harsh conditions of the Caatinga, the present study focused on this important class of bioactive phenolics. Leaves and seeds of plants growing in their natural habitat had their metabolic and proteomic profiles analyzed and integrated with transcriptome data. As a result, 96 metabolites (including 43 flavonoids) were annotated. Transcripts of the flavonoid pathway totaled 27, of which EvCHI, EvCHR, EvCHS, EvCYP75A and EvCYP75B1 were identified as putative main targets for modulating the accumulation of these metabolites. The highest correspondence of mRNA vs. protein was observed in the differentially expressed transcripts. In addition, 394 candidate transcripts encoding for transcription factors distributed among the bHLH, ERF, and MYB families were annotated. Based on interaction network analyses, several putative genes of the flavonoid pathway and transcription factors were related, particularly TFs of the MYB family. Expression patterns of transcripts involved in flavonoid biosynthesis and those involved in responses to biotic and abiotic stresses were discussed in detail. Overall, these findings provide a base for the understanding of molecular and metabolic responses in this medicinally important species. Moreover, the identification of key regulatory targets for future studies aiming at bioactive metabolite production will be facilitated.

Roles of the 2-Oxoglutarate-Dependent Dioxygenase Superfamily in the Flavonoid Pathway: A Review of the Functional Diversity of F3H, FNS I, FLS, and LDOX/ANS

The 2-oxoglutarate-dependent dioxygenase (2-OGD) superfamily is one of the largest protein families in plants. The main oxidation reactions they catalyze in plants are hydroxylation, desaturation, demethylation, epimerization, and halogenation. Four members of the 2-OGD superfamily, i.e., flavonone 3β-hydroxylase (F3H), flavones synthase I (FNS I), flavonol synthase (FLS), and anthocyanidin synthase (ANS)/leucoanthocyanidin dioxygenase (LDOX), are present in the flavonoid pathway, catalyzing hydroxylation and desaturation reactions. In this review, we summarize the recent research progress on these proteins, from the discovery of their enzymatic activity, to their functional verification, to the analysis of the response they mediate in plants towards adversity. Substrate diversity analysis indicated that F3H, FNS Ⅰ, ANS/LDOX, and FLS perform their respective dominant functions in the flavonoid pathway, despite the presence of functional redundancy among them. The phylogenetic tree classified two types of FNS Ⅰ, one mainly performing FNS activity, and the other, a new type of FNS present in angiosperms, mainly involved in C-5 hydroxylation of SA. Additionally, a new class of LDOXs is highlighted, which can catalyze the conversion of (+)-catechin to cyanidin, further influencing the starter and extension unit composition of proanthocyanidins (PAs). The systematical description of the functional diversity and evolutionary relationship among these enzymes can facilitate the understanding of their impacts on plant metabolism. On the other hand, it provides molecular genetic evidence of the chemical evolution of flavonoids from lower to higher plants, promoting plant adaptation to harsh environments.

Characterization of the Brassica napus Flavonol Synthase Gene Family Reveals Bifunctional Flavonol Synthases

Flavonol synthase (FLS) is a key enzyme for the formation of flavonols, which are a subclass of the flavonoids. FLS catalyzes the conversion of dihydroflavonols to flavonols. The enzyme belongs to the 2-oxoglutarate-dependent dioxygenases (2-ODD) superfamily. We characterized the FLS gene family of Brassica napus that covers 13 genes, based on the genome sequence of the B. napus cultivar Express 617. The goal was to unravel which BnaFLS genes are relevant for seed flavonol accumulation in the amphidiploid species B. napus. Two BnaFLS1 homeologs were identified and shown to encode bifunctional enzymes. Both exhibit FLS activity as well as flavanone 3-hydroxylase (F3H) activity, which was demonstrated in vivo and in planta. BnaFLS1-1 and -2 are capable of converting flavanones into dihydroflavonols and further into flavonols. Analysis of spatio-temporal transcription patterns revealed similar expression profiles of BnaFLS1 genes. Both are mainly expressed in reproductive organs and co-expressed with the genes encoding early steps of flavonoid biosynthesis. Our results provide novel insights into flavonol biosynthesis in B. napus and contribute information for breeding targets with the aim to modify the flavonol content in rapeseed.

A leucoanthocyanidin dioxygenase gene (RtLDOX2) from the feral forage plant Reaumuria trigyna promotes the accumulation of flavonoids and improves tolerance to abiotic stresses

Reaumuria trigyna, a Tamaricaceae archaic recretohalophyte, is an important feral forage plant in the desert steppe of northwestern China. We identified two significantly differentially expressed leucoanthocyanidin dioxygenase genes (RtLDOX/RtLDOX2) and investigated the function and characteristics of RtLDOX2. RtLDOX2 from R. trigyna was rapidly upregulated by salt, drought, and abscisic acid, consistent with the stress-related cis-regulatory elements in the promoter region. Recombinant RtLDOX2 converted dihydrokaempferol to kaempferol in vitro, and was thus interchangeable with flavonol synthase, a dioxygenase in the flavonoid pathway. Transgenic plants overexpressing RtLDOX2 accumulated more anthocyanin and flavonols under abiotic stresses, speculating that RtLDOX2 may act as a multifunctional dioxygenase in the synthesis of anthocyanins and flavonols. Overexpression of RtLDOX2 enhanced the primary root length, biomass accumulation, and chlorophyll content of salt-, drought-, and ultraviolet-B-stressed transgenic Arabidopsis. Antioxidant enzyme activity; proline content; and expression of antioxidant enzyme, proline biosynthesis, and ion-transporter genes were increased in transgenic plants. Therefore, RtLDOX2 confers tolerance to abiotic stress on transgenic Arabidopsis by promoting the accumulation of anthocyanins and flavonols. This in turn increases reactive oxygen species scavenging and activates other stress responses, such as osmotic adjustment and ion transport, and so improves tolerance to abiotic stresses.

A Synchronized Increase of Stilbenes and Flavonoids in Metabolically Engineered Vitis vinifera cv. Gamay Red Cell Culture

Stilbenes and flavonoids are two major health-promoting phenylpropanoid groups in grapes. Attempts to promote the accumulation of one group usually resulted in a decrease in the other. This study presents a unique strategy for simultaneously increasing metabolites in both groups in V. vinifera cv. Gamay Red grape cell culture, by overexpression of flavonol synthase (FLS) and increasing Phe availability. Increased Phe availability was achieved by transforming the cell culture with a second gene, the feedback-insensitive E. coli DAHP synthase (AroG*), and feeding them with Phe. A combined metabolomic and transcriptomic analysis reveals that the increase in both phenylpropanoid groups is accompanied by an induction of many of the flavonoid biosynthetic genes and no change in the expression levels of stilbene synthase. Furthermore, FLS overexpression with increased Phe availability resulted in higher anthocyanin levels, mainly those derived from delphinidin, due to the induction of F3'5'H. These insights may contribute to the development of grape berries with increased health benefits.

Ectopic expression of DoFLS1 from Dendrobium officinale enhances flavonol accumulation and abiotic stress tolerance in Arabidopsis thaliana

Flavonols are important active ingredients that are found in abundance in Dendrobium officinale. Research on flavonol biosynthesis currently focuses on the more ubiquitous kaempferol and quercetin, but little is known on the biosynthesis of myricetin. Notably, flavonol synthase (FLS), which is responsible for the biosynthesis of flavonols, has not yet been identified. In this study, we isolated a flavonol synthase, DoFLS1, from Dendrobium officinale. DoFLS1 harbors conserved 2-oxoglutarate-dependent dioxygenase-specific and FLS-specific motifs. DoFLS1 is a cytoplasmic protein. DoFLS1 was universally expressed in roots, stems, and leaves of juvenile and adult D. officinale plants. DoFLS1 expression was strongly correlated in juvenile and adult D. officinale plants (R² = 0.86 and 0.98, respectively; p < 0.01) with the average of corresponding flavonol levels. Transgenic Arabidopsis thaliana expressing DoFLS1 exhibited a 1.24-fold increase in flavonol content and a 25.78% decrease in anthocyanin content compare to wild-type plants, possibly resulting from a 78.61% increase in myricetin level. Moreover, the loss of anthocyanin was attributed to decreased expression of dihydroflavonol reductase (DFR) and anthocyanidin synthase (ANS) genes in transgenic A. thaliana that expressed DoFLS1. DoFLS1 also complemented the deficiency in flavonol of the A. thaliana fls1-3 mutant, which had reduced anthocyanin but increased flavonol content relative to the fls1-3 mutant. In addition, DoFLS1 was significantly upregulated after treatment with cold, drought or salicylic acid. These findings provide genetic evidence for the involvement of DoFLS1 in the biosynthesis of flavonol and in response to abiotic stresses.

CsbZIP1-CsMYB12 mediates the production of bitter-tasting flavonols in tea plants (Camellia sinensis) through a coordinated activator-repressor network

Under high light conditions or UV radiation, tea plant leaves produce more flavonols, which contribute to the bitter taste of tea; however, neither the flavonol biosynthesis pathways nor the regulation of their production are well understood. Intriguingly, tea leaf flavonols are enhanced by UV-B but reduced by shading treatment. CsFLS, CsUGT78A14, CsMYB12, and CsbZIP1 were upregulated by UV-B radiation and downregulated by shading. CsMYB12 and CsbZIP1 bound to the promoters of CsFLS and CsUGT78A14, respectively, and activated their expression individually. CsbZIP1 positively regulated CsMYB12 and interacted with CsMYB12, which specifically activated flavonol biosynthesis. Meanwhile, CsPIF3 and two MYB repressor genes, CsMYB4 and CsMYB7, displayed expression patterns opposite to that of CsMYB12. CsMYB4 and CsMYB7 bound to CsFLS and CsUGT78A14 and repressed their CsMYB12-activated expression. While CsbZIP1 and CsMYB12 regulated neither CsMYB4 nor CsMYB7, CsMYB12 interacted with CsbZIP1, CsMYB4, and CsMYB7, but CsbZIP1 did not physically interact with CsMYB4 or CsMYB7. Finally, CsPIF3 bound to and activated CsMYB7 under shading to repress flavonol biosynthesis. These combined results suggest that UV activation and shading repression of flavonol biosynthesis in tea leaves are coordinated through a complex network involving CsbZIP1 and CsPIF3 as positive MYB activators and negative MYB repressors, respectively. The study thus provides insight into the regulatory mechanism underlying the production of bitter-tasting flavonols in tea plants.

The spatio-temporal biosynthesis of floral flavonols is controlled by differential phylogenetic MYB regulators in Freesia hybrida

Floral flavonols play specific pivotal roles in pollinator attraction, pollen germination and fertility, in addition to other functions in vegetative organs. For many plants, the process of flavonol biosynthesis in late flower development stages and in mature flower tissues is poorly understood, in contrast to early flower development stages. It is thought that this process may be regulated independently of subgroup 7 R2R3 MYB (SG7 MYB) transcription factors. In this study, two FLS genes were shown to be expressed synchronously with the flower development-specific and tissue-specific biosynthesis of flavonols in Freesia hybrida. FhFLS1 contributed to flavonol biosynthesis in early flower buds, toruses and calyxes, and was regulated by four well-known SG7 MYB proteins, designated as FhMYBFs, with at least partial regulatory redundancy. FhFLS2 accounted for flavonols in late developed flowers and in the petals, stamens and pistils, and was targeted directly by non SG7 MYB protein FhMYB21L2. In parallel, AtMYB21 and AtMYB24 also activated AtFLS1, a gene highly expressed in Arabidopsis anthers and pollen, indicating the conserved regulatory roles of MYB21 against FLS genes in these two evolutionarily divergent angiosperm plants. Our results reveal a novel regulatory and synthetic mechanism underlying flavonol biosynthesis in floral organs and tissues which may be exploited to investigate supplementary roles of flavonols in flowers.

Genotypic variation of flavonols and antioxidant capacity in broccoli

Flavonols are gaining increasing interests due to their diverse health benefits for humans. Broccoli is a main flavonol source in our diet, but the genetic variation of flavonols and their correlation with antioxidant capacity remain to be understood. Here, we examined variations of the two major flavonols kaempferol and quercetin in florets and leaves of 15 diverse broccoli accessions by ultra-performance liquid chromatography. Broccoli accumulated more kaempferol than quercetin in most of the accessions tested, with the ratios varying from 4.4 to 27.9 in leaves and 0.4 to 4.4 in florets. Total flavonoids showed 2.5-fold and 3.3-fold differences in leaves and florets of these accessions, respectively. Principle component analysis revealed that flavonols, along with the key biosynthetic pathway genes, correlated with antioxidant capacity related indicators. This study provides important information for broccoli flavonol genotypic variations and correlation with antioxidant capacity, and will facilitate the development of flavonol enriched cultivars in broccoli.

Increased Flavonol Levels in Tobacco Expressing AcFLS Affect Flower Color and Root Growth

The onion (Allium cepa L.) flavonol synthase (AcFLS-HRB) gene, encoding an enzyme responsible for flavonol biosynthesis in yellow onion, was recently identified and enzymatically characterized. Here, we performed an in vivo feeding assay involving bacterial expression of AcFLS-HRB and observed that it exhibited both flavanone 3-hydroxylase (F3H) and FLS activity. Transgenic tobacco (Nicotiana tabacum) expressing AcFLS-HRB produced lighter-pink flowers compared to wild-type plants. In transgenic petals, AcFLS-HRB was highly expressed at the mRNA and protein levels, and most AcFLS-HRB protein accumulated in the insoluble microsomal fractions. High-performance liquid chromatography (HPLC) analysis showed that flavonol levels increased but anthocyanin levels decreased in transgenic petals, indicating that AcFLS-HRB is a functional gene in planta. Gene expression analysis showed the reduced transcript levels of general phenylpropanoid biosynthetic genes and flavonoid biosynthetic genes in AcFLS-HRB overexpressed tobacco petals. Additionally, transgenic tobacco plants at the seedling stages showed increased primary root and root hair length and enhanced quercetin signals in roots. Exogenous supplementation with quercetin 3-O-rutinoside (rutin) led to the same phenotypic changes in root growth, suggesting that rutin is the causal compound that promotes root growth in tobacco. Therefore, augmenting flavonol levels affects both flower color and root growth in tobacco.

Amaranth (Amaranthus cruentus L.) and canola (Brassica napus L.) oil impact on the oxidative metabolism of neutrophils in the obese patients

CONTEXT

Amaranth and canola oils have been used traditionally. Amaranth has been identified as being of interest because of its outstanding nutritive value. Amaranth oil is a rich source of highly unsaturated fats and so could be a valuable dietary alternative for individuals affected with obesity. Reactive oxygen species (ROS) are postulated to be involved in systemic inflammation and oxidative stress. Activated polymorphonuclear neutrophils (PMNs) generate high amounts of reactive oxygen species.

OBJECTIVE

Our study investigates the impact of amaranth and canola oils supplementation on oxidative metabolism in patients with obesity. We hypothesized that, due to its lipid-lowering and antioxidant properties, amaranth and canola oil would protect against oxidative stress.

MATERIALS AND METHODS

We tested 19 obese patients [body mass index (BMI) = 41.1 ± 7.8 kg/m², (mean ± SD)]. The protocol consisted of two stages: a run-in phase of 2 weeks and an experimental stage - canola or amaranth oil supplementation (20 mL/d) with calorie restriction diet for 3 weeks. The neutrophil oxidative burst was expressed by fluorescence intensity (IF).

RESULTS

The oxidative burst had increased significantly at the end of treatment in both groups IF: (21.4 ± 11.15 vs. 35.9 ± 20.3; mean ± SD) p < 0.05. The levels of IF were significantly higher in neutrophils of patients who received canola oil (41.05 ± 25.3) compared to those who received amaranth oil (28.4 ± 11.8) p < 0.05.

CONCLUSIONS

Canola oil exerts possible effects on oxidative burst activity in neutrophils in vivo conditions.

The Research Progress of Chalcone Isomerase (CHI) in Plants

Chalcone isomerase (CHI) is the second rate-limiting and the first reported enzyme involved in the biosynthetic pathway of flavonoids. It catalyzes the intramolecular cyclization reaction, converting the bicyclic chalcone into tricyclic (2S)-flavanone. In this paper, we obtained and analyzed 916 DNA sequences, 1310 mRNA sequences, and 2403 amino acid sequences of CHI registered in NCBI by Jan 2018. The full length of CHI DNA sequences ranges from 218 to 3758 bp, CHI mRNA sequences ranges from 265 to 1436 bp, and CHI amino acid sequences ranges from 35 to 465 amino acid residues. Forty representative species were selected from each family to construct the maximum likelihood tree and analyze the evolutionary relationship. According to the medicinal and agricultural use, 13 specific species were selected, and their physicochemical properties were analyzed. The molecular weight of CHI ranges from 23 to 26 kD, and the isoelectric point of CHI ranges from 4.93 to 5.85. All the half-life periods of CHI are 30 h in mammalian reticulocytes in vitro, 20 h in yeast, and 10 h in E. coli in vivo, theoretically. The consistency of the 13 CHI amino acid sequences is 63.55%. According to the similarity between each sequence, we selected four CHI sequences of Paeonia suffruticosa, Paeonia lactiflora, Taxus wallichiana, and Tradescantia hirsutiflora for secondary structure, three-dimensional protein models, conserved domains, transmembrane structure, and signal peptide prediction analysis. It was found that CHI sequences of Paeonia suffruticosa and Paeonia lactiflora owned a higher similarity; they both share the template 4doi.1.A. The four CHI all have no signal peptides, and they exert their activities in cytoplasm. Then, PubMed, Web of Science, Science Direct, and Research Gate were used as information sources through the search terms 'chalcone isomerase', 'biosynthesis', 'expression', and their combinations to get the latest and comprehensive information of CHI, mainly from the year 2010 to 2018. More than 300 papers were searched and 116 papers were reviewed in the present work. We summarized the classification of CHI, catalytic reaction mechanism of CHI, and progress of genetic engineering regarding CHI clone, expression, and exogenous stimulator regulation. This paper will lay a foundation for further studies of CHI and other functional genes involved in flavonoids biosynthetic pathway.

The heterologous expression of Arabidopsis PAP2 induces anthocyanin accumulation and inhibits plant growth in tomato

Anthocyanins are naturally occurring secondary metabolites, responsible for the color of many plants. The Arabidopsis thaliana MYB90/PAP2 (production of anthocyanin pigment 2) was introduced into tomato to study its effect on anthocyanin accumulation. The transgenic tomato displayed much greater anthocyanin accumulation than wild type in all plant organs, but the organs were not fully purple in color except for the stamen. The expression of anthocyanin biosynthetic genes and an anthocyanin-related basic helix-loop-helix (bHLH) gene SlAN1 was significantly increased in the transgenic line, suggesting that ectopic expression of AtPAP2 increases the expression of anthocyanin-related structural and regulatory genes to enhance anthocyanin content. Yeast two-hybrid assays revealed that the endogenous MYB protein SlAN2 interacted with two putative bHLH partners, SlAN1 and SlJAF13, while AtPAP2 only interacted with SlJAF13, which may be why AtPAP2 transgenic plants showed limited anthocyanin accumulation in fruits. In addition to anthocyanin accumulation, the transgenic tomato plants were significantly smaller in size, and the length of primary roots and number of lateral roots were obviously decreased. The expression of lignin biosynthetic genes was downregulated in transgenic tomato plants, which may be the reason for the inhibited growth. The lateral organ boundaries-domain (LBD) genes, which regulate lateral root organogenesis in the auxin signaling pathway, were downregulated in transgenic tomato roots, which may partly account for the disturbed lateral root formation in the transformants. Taken together, the results demonstrate that heterologous expression of transcription factor AtPAP2 not only resulted in anthocyanin accumulation but also inhibited plant growth in tomato.

High accumulation of anthocyanins via the ectopic expression of AtDFR confers significant salt stress tolerance in Brassica napus L

The ectopic expression of AtDFR results in increased accumulation of anthocyanins leading to enhanced salinity and drought stress tolerance in B. napus plants. Flavonoids with antioxidant effects confer many additional benefits to plants. Evidence indicates that flavonoids, including anthocyanins, protect tissues against oxidative stress from various abiotic stressors. We determined whether increases in anthocyanins increased abiotic stress tolerance in Brassica napus, because the values of B. napus L. and its cultivation area are increasing worldwide. We overexpressed Arabidopsis dihydroflavonol-4-reductase (DFR) in B. napus. Increased DFR transcript levels for AtDFR-OX B. shoots correlated with higher anthocyanin accumulation. AtDFR-OX Brassica shoots exhibited lower reactive oxygen species (ROS) accumulation than wild-type (WT) shoots under high NaCl and mannitol concentrations. This was corroborated by 3,3-diaminobenzidine staining for ROS scavenging activity in 1,1-diphenyl-2-picryl-hydrazyl assays. Shoots of the AtDFR-OX B. napus lines grown in a high salt medium exhibited enhanced salt tolerance and higher chlorophyll content than similarly grown WT plants. Our observations suggested that the AtDFR gene can be effectively manipulated to modulate salinity and drought stress tolerance by directing to high accumulation of anthocyanins in oilseed plants.

Combining paired analytical metabolomics and common garden trial to study the metabolism and gene variation of Ginkgo biloba L. cultivated varieties

Paired analytical targeted metabolomics and common garden trial were combined to uncover the gene basis for plant secondary metabolite synthesis.

Comparative Transcriptome Analysis between Broccoli (Brassica oleracea var. italica) and Wild Cabbage (Brassica macrocarpa Guss.) in Response to Plasmodiophora brassicae during Different Infection Stages

Clubroot, one of the most devastating diseases to the Brassicaceae family, is caused by the obligate biotrophic pathogen Plasmodiophora brassicae. However, studies of the molecular basis of disease resistance are still poor especially in quantitative resistance. In the present paper, two previously identified genotypes, a clubroot-resistant genotype (wild cabbage, B2013) and a clubroot-susceptible genotype (broccoli, 90196) were inoculated by P. brassicae for 0 (T0), 7 (T7), and 14 (T14) day after inoculation (DAI). Gene expression pattern analysis suggested that response changes in transcript level of two genotypes under P. brassicae infection were mainly activated at the primary stage (T7). Based on the results of DEGs functional enrichments from two infection stages, genes associated with cell wall biosynthesis, glucosinolate biosynthesis, and plant hormone signal transduction showed down-regulated at T14 compared to T7, indicating that defense responses to P. brassicae were induced earlier, and related pathways were repressed at T14. In addition, the genes related to NBS-LRR proteins, SA signal transduction, cell wall and phytoalexins biosynthesis, chitinase, Ca2+ signals and RBOH proteins were mainly up-regulated in B2013 by comparing those of 90196, indicating the pathways of response defense to clubroot were activated in the resistant genotype. This is the first report about comparative transcriptome analysis for broccoli and its wild relative during the different stages of P. brassicae infection and the results should be useful for molecular assisted screening and breeding of clubroot-resistant genotypes.

Comparative Transcriptome Analysis between Broccoli (Brassica oleracea var. italica) and Wild Cabbage (Brassica macrocarpa Guss.) in Response to Plasmodiophora brassicae during Different Infection Stages

Clubroot, one of the most devastating diseases to the Brassicaceae family, is caused by the obligate biotrophic pathogen Plasmodiophora brassicae. However, studies of the molecular basis of disease resistance are still poor especially in quantitative resistance. In the present paper, two previously identified genotypes, a clubroot-resistant genotype (wild cabbage, B2013) and a clubroot-susceptible genotype (broccoli, 90196) were inoculated by P. brassicae for 0 (T0), 7 (T7), and 14 (T14) day after inoculation (DAI). Gene expression pattern analysis suggested that response changes in transcript level of two genotypes under P. brassicae infection were mainly activated at the primary stage (T7). Based on the results of DEGs functional enrichments from two infection stages, genes associated with cell wall biosynthesis, glucosinolate biosynthesis, and plant hormone signal transduction showed down-regulated at T14 compared to T7, indicating that defense responses to P. brassicae were induced earlier, and related pathways were repressed at T14. In addition, the genes related to NBS-LRR proteins, SA signal transduction, cell wall and phytoalexins biosynthesis, chitinase, Ca²⁺ signals and RBOH proteins were mainly up-regulated in B2013 by comparing those of 90196, indicating the pathways of response defense to clubroot were activated in the resistant genotype. This is the first report about comparative transcriptome analysis for broccoli and its wild relative during the different stages of P. brassicae infection and the results should be useful for molecular assisted screening and breeding of clubroot-resistant genotypes.

Characterization of Arabidopsis thaliana FLAVONOL SYNTHASE 1 (FLS1) -overexpression plants in response to abiotic stress

Flavonoids are an important group of secondary metabolites that are involved in plant growth and contribute to human health. Many studies have focused on the biosynthesis pathway, biochemical characters, and biological functions of flavonoids. In this report, we showed that overexpression of FLS1 (FLS1-OX) not only altered seed coat color (resulting in a light brown color), but also affected flavonoid accumulation. Whereas fls1-3 mutants accumulated higher anthocyanin levels, FLS1-OX seedlings had lower levels than those of the wild-type. Besides, shoot tissues of FLS1-OX plants exhibited lower flavonol levels than those of the wild-type. However, growth performance and abiotic stress tolerance of FLS1-OX, fls1-3, and wild-type plants were not significantly different. Taken together, FLS1 can be manipulated (i.e., silenced or overexpressed) to redirect the flavonoid biosynthetic pathway toward anthocyanin production without negative effects on plant growth and development.

Disequilibrium of Flavonol Synthase and Dihydroflavonol-4-Reductase Expression Associated Tightly to White vs. Red Color Flower Formation in Plants

Flower color is the main character throughout the plant kingdom. Though substantial information exists regarding the structural and regulatory genes involved in anthocyanin and flavonol biosynthesis, little is known that what make a diverse white vs. red color flower in natural species. Here, the contents of pigments in seven species from varied phylogenetic location in plants with red and white flowers were determined. Flavonols could be detected in red and white flowers, but anthocyanins were almost undetectable in the white cultivar. Comparisons of expression patterns of gene related to the flavonoid biosynthesis indicated that disequilibrium expression of flavonol synthase (FLS) and dihydroflavonol-4-reductase (DFR) genes determined the accumulation of flavonols and anothcyanins in both red and white flowers of seven species. To further investigate the role of such common regulatory patterns in determining flower color, FLS genes were isolated from Rosa rugosa (RrFLS1), Prunus persica (PpFLS), and Petunia hybrida (PhFLS), and DFR genes were isolated from Rosa rugosa (RrDFR1) and Petunia hybrida (PhDFR). Heterologous expression of the FLS genes within tobacco host plants demonstrated conservation of function, with the transgenes promoting flavonol biosynthesis and inhibiting anthocyanin accumulation, so resulting in white flowers. Conversely, overexpression of DFR genes in tobacco displayed down-regulation of the endogenous NtFLS gene, and the promotion of anthocyanin synthesis. On this basis, we propose a model in which FLS and DFR gene-products compete for common substrates in order to direct the biosynthesis of flavonols and anthocyanins, respectively, thereby determining white vs. red coloration of flowers.

MYB-related transcription factors function as regulators of the circadian clock and anthocyanin biosynthesis in Arabidopsis

In Arabidopsis, the MYB (myeloblastosis) gene family contains more than 190 members, which play a number of roles in plant growth and development. Based on their protein structure, this gene family was divided into several subclasses, including the MYB-related class. Currently, an MYB-related gene designated as MYB-like Domain (AtMYBD) has been shown to function as a positive regulator of anthocyanin biosynthesis in Arabidopsis. This gene was found to belong to the CCA1-like (circadian clock-associated 1) group, which represents several genes that are master regulators of the circadian clocks of plants. Here, we speculate that AtMYBD is able to regulate anthocyanin biosynthesis in Arabidopsis thaliana in a circadian clock-related manner.