Flavonoid Functions in Plants and Their Interactions with Other Organisms

Hormonal interactions underlying parthenocarpic fruit formation in horticultural crops

In some horticultural crops, such as Cucurbitaceae, Solanaceae, and Rosaceae species, fruit set and development can occur without the fertilization of ovules, a process known as parthenocarpy. Parthenocarpy is an important agricultural trait that can not only mitigate fruit yield losses caused by environmental stresses but can also induce the development of seedless fruit, which is a desirable trait for consumers. In the present review, the induction of parthenocarpic fruit by the application of hormones such as auxins (2,4 dichlorophenoxyacetic acid; naphthaleneacetic acid), cytokinins (forchlorfenuron; 6-benzylaminopurine), gibberellic acids, and brassinosteroids is first presented. Then, the molecular mechanisms of parthenocarpic fruit formation, mainly related to plant hormones, are presented. Auxins, gibberellic acids, and cytokinins are categorized as primary players in initiating fruit set. Other hormones, such as ethylene, brassinosteroids, and melatonin, also participate in parthenocarpic fruit formation. Additionally, synergistic and antagonistic crosstalk between these hormones is crucial for deciding the fate of fruit set. Finally, we highlight knowledge gaps and suggest future directions of research on parthenocarpic fruit formation in horticultural crops.

Deciphering the Crosstalk Mechanisms of Wheat-Stem Rust Pathosystem: Genome-Scale Prediction Unravels Novel Host Targets

Triticum aestivum (wheat), a major staple food grain, is affected by various biotic stresses. Among these, fungal diseases cause about 15-20% of yield loss, worldwide. In this study, we performed a comparative analysis of protein-protein interactions between two Puccinia graminis races (Pgt 21-0 and Pgt Ug99) that cause stem (black) rust in wheat. The available molecular techniques to study the host-pathogen interaction mechanisms are expensive and labor-intensive. We implemented two computational approaches (interolog and domain-based) for the prediction of PPIs and performed various functional analysis to determine the significant differences between the two pathogen races. The analysis revealed that T. aestivum-Pgt 21-0 and T. aestivum-Pgt Ug99 interactomes consisted of ∼90M and ∼56M putative PPIs, respectively. In the predicted PPIs, we identified 115 Pgt 21-0 and 34 Pgt Ug99 potential effectors that were highly involved in pathogen virulence and development. Functional enrichment analysis of the host proteins revealed significant GO terms and KEGG pathways such as O-methyltransferase activity (GO:0008171), regulation of signal transduction (GO:0009966), lignin metabolic process (GO:0009808), plastid envelope (GO:0009526), plant-pathogen interaction pathway (ko04626), and MAPK pathway (ko04016) that are actively involved in plant defense and immune signaling against the biotic stresses. Subcellular localization analysis anticipated the host plastid as a primary target for pathogen attack. The highly connected host hubs in the protein interaction network belonged to protein kinase domain including Ser/Thr protein kinase, MAPK, and cyclin-dependent kinase. We also identified 5,577 transcription factors in the interactions, associated with plant defense during biotic stress conditions. Additionally, novel host targets that are resistant to stem rust disease were also identified. The present study elucidates the functional differences between Pgt 21-0 and Pgt Ug99, thus providing the researchers with strain-specific information for further experimental validation of the interactions, and the development of durable, disease-resistant crop lines.

Inductive and synergistic interactions between plant allelochemical flavone and Bt toxin Cry1Ac in Helicoverpa armigera

Genetically engineered crops simultaneously produce defensive allelochemicals and Bacillus thuringiensis (Bt) toxin proteins to kill some of the world's most devastating insect pests. How the two types of toxins, when ingested sequentially or simultaneously, interact at both lethal and sublethal doses in these pests remains underexplored. Here, we examined the toxicological interactions between the Bt toxin Cry1Ac and the flavonoid allelochemical flavone in Helicoverpa armigera. Simultaneous exposure of H. armigera neonates to lethal doses (LC₂₅ ) of Cry1Ac and flavone caused a mortality significantly higher than that of either toxin alone and their expected additive mortality. Preexposure for 24 h to a sublethal dose (LC₁₀ ) of Cry1Ac followed by 6-d simultaneous exposure to the same dose of Cry1Ac plus a lethal dose (1.6 mg/g diets, LC₅₀ ) of flavone resulted in a mortality significantly higher than that of the LC₅₀ dose of flavone alone and the expected additive mortality of the LC₅₀ dose of flavone plus the LC₁₀ dose of Cry1Ac. One-day preexposure to the sublethal dose (LC₁₀ ) of flavone followed by 6-d simultaneous exposure to the LC₅₀ dose (6 ng/cm² ) of Cry1Ac plus the LC₁₀ dose of flavone yielded a mortality significantly higher than that of the LC₅₀ dose of Cry1Ac but similar to the expected additive mortality of the LC₅₀ dose of Cry1Ac plus the LC₁₀ dose of flavone. The results suggest that Cry1Ac induces and synergizes the toxicity of flavone against H. armigera larvae.

Combined Transcriptome and Proteome Analysis to Elucidate Salt Tolerance Strategies of the Halophyte Panicum antidotale Retz

Panicum antidotale, a C4 monocot, has the potential to reclaim saline and drylands and to be utilized as fodder and forage. Its adaptability to survive saline stress has been proven with eco-physiological and biochemical studies. However, little is known about its molecular mechanisms of salt tolerance. In this study, an integrated transcriptome and proteome analysis approach, based on RNA sequencing and liquid chromatography tandem mass spectrometry (LC-MS/MS), was used to identify the said mechanisms. Plants were treated with control (0 mM), low (100 mM), and high (300 mM) sodium chloride (NaCl) treatments to distinguish beneficial and toxic pathways influencing plant biomass. The results indicated differential expression of 3,179 (1,126 upregulated/2,053 downregulated) and 2,172 (898 upregulated/1,274 downregulated) genes (DEGs), and 514 (269 upregulated/245 downregulated) and 836 (494 upregulated/392 downregulated) proteins (DEPs) at 100 and 300 mM NaCl, respectively. Among these, most upregulated genes and proteins were involved in salt resistance strategies such as proline biosynthesis, the antioxidant defense system, ion homeostasis, and sugar accumulation at low salinity levels. On the other hand, the expression of several genes and proteins involved in the respiratory process were downregulated, indicating the inability of plants to meet their energy demands at high salinity levels. Moreover, the impairments in photosynthesis were also evident with the reduced expression of genes regulating the structure of photosystems and increased expression of abscisic acid (ABA) mediated pathways which limits stomatal gas exchange. Similarly, the disturbance in fatty acid metabolism and activation of essential ion transport blockers damaged the integrity of the cell membrane, which was also evident with enhanced malondialdehyde (MDA). Overall, the analysis of pathways revealed that the plant optimal performance at low salinity was related to enhanced metabolism, antioxidative defense, cell growth, and signaling pathways, whereas high salinity inhibited biomass accumulation by altered expression of numerous genes involved in carbon metabolism, signaling, transcription, and translation. The data provided the first global analysis of the mechanisms imparting salt stress tolerance of any halophyte at transcriptome and proteome levels.

Potential of Producing Flavonoids Using Cyanobacteria As a Sustainable Chassis

Numerous plant secondary metabolites have remarkable impacts on both food supplements and pharmaceuticals for human health improvement. However, higher plants can only generate small amounts of these chemicals with specific temporal and spatial arrangements, which are unable to satisfy the expanding market demands. Cyanobacteria can directly utilize CO₂, light energy, and inorganic nutrients to synthesize versatile plant-specific photosynthetic intermediates and organic compounds in large-scale photobioreactors with outstanding economic merit. Thus, they have been rapidly developed as a "green" chassis for the synthesis of bioproducts. Flavonoids, chemical compounds based on aromatic amino acids, are considered to be indispensable components in a variety of nutraceutical, pharmaceutical, and cosmetic applications. In contrast to heterotrophic metabolic engineering pioneers, such as yeast and Escherichia coli, information about the biosynthesis flavonoids and their derivatives is less comprehensive than that of their photosynthetic counterparts. Here, we review both benefits and challenges to promote cyanobacterial cell factories for flavonoid biosynthesis. With increasing concerns about global environmental issues and food security, we are confident that energy self-supporting cyanobacteria will attract increasing attention for the generation of different kinds of bioproducts. We hope that the work presented here will serve as an index and encourage more scientists to join in the relevant research area.

Single-Molecule Real-Time and Illumina Sequencing to Analyze Transcriptional Regulation of Flavonoid Synthesis in Blueberry

Blueberries (Vaccinium corymbosum) contain large amounts of flavonoids, which play important roles in the plant's ability to resist stress and can also have beneficial effects on human health when the fruits are eaten. However, the molecular mechanisms that regulate flavonoid synthesis in blueberries are still unclear. In this study, we combined two different transcriptome sequencing platforms, single-molecule real-time (SMRT) and Illumina sequencing, to elucidate the flavonoid synthetic pathways in blueberries. We analyzed transcript quantity, length, and the number of annotated genes. We mined genes associated with flavonoid synthesis (such as anthocyanins, flavonols, and proanthocyanidins) and employed fluorescence quantitative PCR to analyze the expression of these genes and their correlation with flavonoid synthesis. We discovered one R2R3 MYB transcription factor from the sequencing library, VcMYB1, that can positively regulate anthocyanin synthesis in blueberries. VcMYB1 is mainly expressed in colored (mature) fruits. Experiments showed that overexpression and transient expression of VcMYB1 promoted anthocyanin synthesis in Arabidopsis, tobacco (Nicotiana benthamiana) plants and green blueberry fruits. Yeast one-hybrid (Y1H) assay, electrophoretic mobility shift assay, and transient expression experiments showed that VcMYB1 binds to the MYB binding site on the promoter of the structural gene for anthocyanin synthesis, VcMYB1 to positively regulate the transcription of VcDFR, thereby promoting anthocyanin synthesis. We also performed an in-depth investigation of transcriptional regulation of anthocyanin synthesis. This study provides background information and data for studying the synthetic pathways of flavonoids and other secondary metabolites in blueberries.

Microalgae biofilm formation and antioxidant responses to stress induce by Lemna minor L., Chlorella vulgaris, and Aphanizomenon flos-aquae

The study shows how microalgae biofilm formation and antioxidant responses to the production of reactive oxygen species (ROS) is alter by the presences of Lemna minor L., Chlorella vulgaris, and Aphanizomenon flos-aquae. The study involves the cultivation of the biofilm of Chlorella vulgaris and Aphanizomenon flos-aquae in three bioreactors. The condition of growth for the biofilm formation was varied across the three bioreactors to enable the dominance Chlorella vulgaris and Aphanizomenon flos-aquae in one of the bioreactors. Lemna minor L. was also introduce into one of the bioreactors to determine its effect on the biofilm formation. The result obtained shows that C. vulgaris and A. flos-aquae dominate the biofilm, resulting in a high level of H₂O₂ and O₂^- (H₂O₂ was 0.122 ± 0.052 and 0.183 ± 0.108 mmol/L in C. vulgaris and A. flos-aquae, respectively, and O₂^- was 0.261 ± 0.039 and 0.251 ± 0.148 mmol/L in C. vulgaris and A. flos-aquae, respectively). The study also revealed that the presence of L. minor L. tend to reduce the oxidative stress to the biofilm leading to low production of ROS (H₂O₂ was 0.086 ± 0.027 and 0.089 ± 0.045 mmol/L in C. vulgaris and A. flos-aquae respectively, and O₂^- was 0.185 ± 0.044 and 0.161 ± 0.065 mmol/L in C. vulgaris and A. flos-aquae respectively). The variation in the ability of the biofilm of C. vulgaris and A. flos-aquae to respond via chlorophyll, carotenoid, flavonoid, anthocyanin, superoxide dismutase, peroxidase, catalase, glutathione reductase activities, antioxidant reducing power, phosphomolybdate activity, DPPH reduction activity, H₂O₂ scavenging activity, lipid content and organic carbon also supports the fact that the presence of biomass of microalgae and aquatic macrophytes tend to affect the process of microalgae biofilm formation and the ability of the biofilm to produce antioxidant. This high nutrient utilization leads to the production of biomass which can be used for biofuel production and other biotechnological products.

CRISPR/Cas9 technology for improving agronomic traits and future prospective in agriculture

In this review, we have focused on the CRISPR/Cas9 technology for improving the agronomic traits in plants through point mutations, knockout, and single base editing, and we highlighted the recent progress in plant metabolic engineering. CRISPR/Cas9 technology has immense power to reproduce plants with desired characters and revolutionizing the field of genome engineering by erasing the barriers in targeted genome editing. Agriculture fields are using this advance genome editing tool to get the desired traits in the crops plants such as increase yield, improve product quality attributes, and enhance resistance against biotic and abiotic stresses by identifying and editing genes of interest. This review focuses on CRISPR/Cas-based gene knockout for trait improvement and single base editing to boost yield, quality, stress tolerance, and disease resistance traits in crops. Use of CRISPR/Cas9 system to facilitate crop domestication and hybrid breeding are also touched. We summarize recent developments and up-gradation of delivery mechanism (nanotechnology and virus particle-based delivery system) and progress in multiplex gene editing. We also shed lights in advances and challenges of engineering the important metabolic pathways that contain a variety of dietary metabolites and phytochemicals. In addition, we endorsed substantial technical hurdles and possible ways to overcome the unpredictability of CRISPR/Cas technology for broader application across various crop species. We speculated that by making a strong interconnection among all genomic fields will give a gigantic bunt of knowledge to develop crop expressing desired traits.

The phenylpropanoid pathway inhibitor piperonylic acid induces broad-spectrum pest and disease resistance in plants

Although many phenylpropanoid pathway-derived molecules act as physical and chemical barriers to pests and pathogens, comparatively little is known about their role in regulating plant immunity. To explore this research field, we transiently perturbed the phenylpropanoid pathway through application of the CINNAMIC ACID-4-HYDROXYLASE (C4H) inhibitor piperonylic acid (PA). Using bioassays involving diverse pests and pathogens, we show that transient C4H inhibition triggers systemic, broad-spectrum resistance in higher plants without affecting growth. PA treatment enhances tomato (Solanum lycopersicum) resistance in field and laboratory conditions, thereby illustrating the potential of phenylpropanoid pathway perturbation in crop protection. At the molecular level, transcriptome and metabolome analyses reveal that transient C4H inhibition in tomato reprograms phenylpropanoid and flavonoid metabolism, systemically induces immune signalling and pathogenesis-related genes, and locally affects reactive oxygen species metabolism. Furthermore, C4H inhibition primes cell wall modification and phenolic compound accumulation in response to root-knot nematode infection. Although PA treatment induces local accumulation of the phytohormone salicylic acid, the PA resistance phenotype is preserved in tomato plants expressing the salicylic acid-degrading NahG construct. Together, our results demonstrate that transient phenylpropanoid pathway perturbation is a conserved inducer of plant resistance and thus highlight the crucial regulatory role of this pathway in plant immunity.

Comparison of Antioxidant Properties of a Conjugate of Taxifolin with Glyoxylic Acid and Selected Flavonoids

It is known that flavonoids can react with toxic carbonyl compounds in the process of the storage, aging, and digestion of flavonoid-rich foods and beverages. However, the effect of these reactions on the antioxidant properties of the polyphenolic fraction and the properties of the resulting products remain poorly studied. The aim of the present work was to study the antioxidant activity of quercetin, taxifolin, catechin, eriodictyol, hesperetin, naringenin and a product of the condensation of taxifolin with glyoxylic acid, as well as to reveal the structure–activity relationship of these polyphenols. It was found that flavonoids containing the catechol moiety exhibited higher antioxidant activity than hesperetin and naringenin. The product showed the highest hydrogen peroxide scavenging activity, a lower metal-reducing and a higher iron-binding ability than catechol-containing flavonoids, and a lipid peroxidation inhibitory activity comparable with that of taxifolin. Thus, the condensation of flavonoids with toxic carbonyl compounds might lead to the formation of products exhibiting high antioxidant activity. Meanwhile, the conditions under which parent flavonoids and their products exhibit the maximal antioxidant activity may differ. The data suggest that the antioxidant profile of the polyphenolic fraction and bioavailability of polyphenols, carbonyl compounds, and metal ions may change when these reactions occur.

Halophytes as source of bioactive phenolic compounds and their potential applications

Halophytes are salt-tolerant plants that inhabit environments in which they are exposed to extreme stress, wherefore they exhibit conserved and divergent metabolic responses different from those of conventional plants. Thus, the synthesis and accumulation of metabolites, especially of those oxidative stress-related such as phenolic compounds, should be investigated. The potential of halophytes as a source of phenolics and their prospective industrial applications are evaluated based on a comprehensive review of the scientific literature on the phenolic compounds of more than forty halophytes and their biological activities. Additionally, an overview of the analytical methodologies adopted for phenolics determination in halophytes is provided. Finally, the prospective uses and beneficial effects of the phenolic preparations from these plants are discussed. Halophytes are complex matrices, exhibiting a wide variety of phenolics in their composition, wherefore the results can be greatly affected depending on the organ plant under analysis and the extraction methodology, especially the extraction solvent used. High-performance liquid chromatography, coupled with diode array detection (HPLC-DAD) or mass spectrometry (HPLC-MS), are the most used technique. Halophytes biosynthesize phenolics in concentrations that justify the remarkable antioxidant and antimicrobial activities shown, making them ideal sources of bioactive molecules to be employed in a multitude of sectors.

Side effects of triazoles on treated crops

Triazolic fungicides are widely applied in crop production to protect plants against fungal pathogens. However, they may influence the biochemical processes in plants and other non-target species. This paper is aimed at the effect of triazoles (namely tebuconazole, cyproconazole, and penconazole) single/mixed applications on the phenolics production in tomato (Solanum lycopersicum L.) fruit peel, amount of chlorophyll a and b in tomato leaves as well as on basic plant growth parameters. For this purpose, cherry tomatoes were planted in the pot experiment and foliarly-treated weekly, with the same total triazoles dose of 3.52 μmol per plant (in mixtures of 1.71 or 1.17 μmol of each in two or three components, respectively). The treatments increased the weight of fruits in the 1st harvest about 43%, however, this effect was not observed in the next harvest. Increased oxidative stress in the triazoles presence was observed, based on the elevated production of antioxidant phenolics in the 1st harvest. Most alarming is the decrease of the weight of thin stems and foliage and the concentration of chlorophyll a (b) in leaves in all triazoles-treated variants. The non-target impacts on plant biochemical processes (related to the phenolics or chlorophylls production and functionality) were confirmed.

Transcriptome and metabolite profiling reveal that spraying calcium fertilizer reduces grape berry cracking by modulating the flavonoid biosynthetic metabolic pathway

Grape (Vitis vinifera L.) is one of the most widely cultivated fruit crops globally. Fruit cracking during fruit growth and development severely affects yield and quality, resulting in significant economic losses. Currently, calcium fertilizer application is used to prevent berry cracking. However, the mechanisms by which calcium fertilizer treatment reduces berry cracking are poorly understood. To explore this, transcriptomics and metabolomics were used to identify the differentially expressed genes (DEGs) and differentially abundant metabolites in V. vinifera '90-1'. We found that secondary metabolic pathways were enriched during the veraison and maturity stages, including the flavonoid biosynthesis pathway. Enrichment analysis indicated that most of the DEGs were enriched in the functional category of flavonoid biosynthesis. As secondary metabolites are largely antioxidants, the spraying of calcium fertilizers may improve the antioxidant capacity of the berries by regulating genes related to the flavonoid metabolism pathway, thus reducing the occurrence of berry cracking.

Dissecting Metabolism of Leaf Nodules in Ardisia crenata and Psychotria punctata

Root-microbe interaction and its specialized root nodule structures and functions are well studied. In contrast, leaf nodules harboring microbial endophytes in special glandular leaf structures have only recently gained increased interest as plant-microbe phyllosphere interactions. Here, we applied a comprehensive metabolomics platform in combination with natural product isolation and characterization to dissect leaf and leaf nodule metabolism and functions in Ardisia crenata (Primulaceae) and Psychotria punctata (Rubiaceae). The results indicate that abiotic stress resilience plays an important part within the leaf nodule symbiosis of both species. Both species showed metabolic signatures of enhanced nitrogen assimilation/dissimilation pattern and increased polyamine levels in nodules compared to leaf lamina tissue potentially involved in senescence processes and photosynthesis. Multiple links to cytokinin and REDOX-active pathways were found. Our results further demonstrate that secondary metabolite production by endophytes is a key feature of this symbiotic system. Multiple anhydromuropeptides (AhMP) and their derivatives were identified as highly characteristic biomarkers for nodulation within both species. A novel epicatechin derivative was structurally elucidated with NMR and shown to be enriched within the leaf nodules of A. crenata. This enrichment within nodulated tissues was also observed for catechin and other flavonoids indicating that flavonoid metabolism may play an important role for leaf nodule symbiosis of A. crenata. In contrast, pavettamine was only detected in P. punctata and showed no nodule specific enrichment but a developmental effect. Further natural products were detected, including three putative unknown depsipeptide structures in A. crenata leaf nodules. The analysis presents a first metabolomics reference data set for the intimate interaction of microbes and plants in leaf nodules, reveals novel metabolic processes of plant-microbe interaction as well as the potential of natural product discovery in these systems.

Effect of Thermal Processing on Color, Phenolic Compounds, and Antioxidant Activity of Faba Bean (Vicia faba L.) Leaves and Seeds

The leaves and seeds of the faba bean are good sources of L-3,4-dihydroxyphenylalanin (L-dopa), and are usually eaten with thermal cooking methods. However, little information is available on the effect of thermal treatments on their nutritional value. We compared the changes in color, contents of L-dopa, vitamin C (Vc), total phenolics (TP), total flavonoids (TF) and antioxidant activity after dry heating or steaming faba bean leaves and seeds. The young leaves provided higher values of all the estimate factors, regardless of the thermal treatment. Steaming significantly degraded nutritional values of the leaves, but less changed in seeds, whereas dry heat maintained these attributes. The contents of L-dopa, Vc, TP and TF were shown to have strongly positive correlations with antioxidant activity in the leaves, whereas only L-dopa content was positively correlated with antioxidant activity of the seeds. Faba leaves contained relatively high L-dopa which possessed strong antioxidant activity compared to the Vc. As L-dopa is an important contributor to the antioxidant activity of faba leaves and seeds, consuming L-dopa from leaves may provide beneficial effects not only regarding Parkinson's Disease.

Differential Impact of Plant Secondary Metabolites on the Soil Microbiota

Plant metabolites can shape the microbial community composition in the soil. Two indole metabolites, benzoxazolinone (BOA) and gramine, produced by different Gramineae species, and quercetin, a flavonoid synthesized by many dicot species, were studied for their impacts on the community structure of field soil bacteria. The three plant metabolites were directly added to agricultural soil over a period of 28 days. Alterations in bacterial composition were monitored by next generation sequencing of 16S rRNA gene PCR products and phospholipid fatty acid analysis. Treatment of the soil with the plant metabolites altered the community composition from phylum to amplicon sequence variant (ASV) level. Alpha diversity was significantly reduced by BOA or quercetin, but not by gramine. BOA treatment caused a decrease of the relative abundance of 11 ASVs, while only 10 ASVs were increased. Gramine or quercetin treatment resulted in the increase in relative abundance of many more ASVs (33 or 38, respectively), most of them belonging to the Proteobacteria. Isolation and characterization of cultivable bacteria indicated an enrichment in Pseudarthrobacter or Pseudomonas strains under BOA/quercetin or BOA/gramine treatments, respectively. Therefore, the effects of the treatments on soil bacteria were characteristic for each metabolite, with BOA exerting a predominantly inhibitory effect, with only few genera being able to proliferate, while gramine and quercetin caused the proliferation of many potentially beneficial strains. As a consequence, BOA or gramine biosynthesis, which have evolved in different barley species, is accompanied with the association of distinct bacterial communities in the soil, presumably after mutual adaptation during evolution.

Diversity of Chemical Structures and Biosynthesis of Polyphenols in Nut-Bearing Species

Nuts, such as peanut, almond, and chestnut, are valuable food crops for humans being important sources of fatty acids, vitamins, minerals, and polyphenols. Polyphenols, such as flavonoids, stilbenoids, and hydroxycinnamates, represent a group of plant-specialized (secondary) metabolites which are characterized as health-beneficial antioxidants within the human diet as well as physiological stress protectants within the plant. In food chemistry research, a multitude of polyphenols contained in culinary nuts have been studied leading to the identification of their chemical properties and bioactivities. Although functional elucidation of the biosynthetic genes of polyphenols in nut species is crucially important for crop improvement in the creation of higher-quality nuts and stress-tolerant cultivars, the chemical diversity of nut polyphenols and the key biosynthetic genes responsible for their production are still largely uncharacterized. However, current technical advances in whole-genome sequencing have facilitated that nut plant species became model plants for omics-based approaches. Here, we review the chemical diversity of seed polyphenols in majorly consumed nut species coupled to insights into their biological activities. Furthermore, we present an example of the annotation of key genes involved in polyphenolic biosynthesis in peanut using comparative genomics as a case study outlining how we are approaching omics-based approaches of the nut plant species.

Tangeretin as an adjuvant and chemotherapeutic sensitizer against various types of cancers: a comparative overview

OBJECTIVES

Cancer is a leading cause of disabling morbidities and death worldwide. Although there are various strategies for the management of cancer, the severe adverse effects negatively impact the patient's quality of life. In addition, the development of resistance limits the efficacy of many chemotherapeutics. Many natural agents are capable of reducing the adverse effects associated with chemotherapy and improving the therapeutic outcome. Tangeretin, a polymethoxy flavone, is one of the promising natural anticancer agents.

KEY FINDINGS

Tangeretin not only targets various malignancies but also synergizes chemotherapeutic agents and reverses cancer resistance. Hence, the application of tangeretin as an adjuvant in cancer chemotherapy would be a promising strategy.

SUMMARY

This work critically highlighted the proposed anticancer activity of tangeretin and discussed its potential combination with various chemotherapeutic agents. Additionally, it shed light on tangeretin chemical derivatives with improved pharmacokinetic and pharmacodynamic activity. Finally, this review described flavonoid biosynthetic pathways and how bioengineering can be employed to enhance the production yield of tangeretin. Thus, this work paves the way for the rational clinical utilization of tangeretin as a safe and effective adjuvant in chemotherapeutic protocols.

Innate Resistance and Phosphite Treatment Affect Both the Pathogen's and Host's Transcriptomes in the Tanoak-Phytophthora ramorum Pathosystem

Phosphites have been used to control Sudden Oak Death; however, their precise mode of action is not fully understood. To study the mechanism of action of phosphites, we conducted an inoculation experiment on two open-pollinated tanoak families, previously found to be partially resistant. Stems of treatment group individuals were sprayed with phosphite, and seven days later, distal leaves were inoculated with the Sudden Oak Death pathogen Phytophthora ramorum. Leaves from treated and untreated control plants were harvested before and seven days after inoculation, and transcriptomes of both host and pathogen were analyzed. We found that tanoak families differed in the presence of innate resistance (resistance displayed by untreated tanoak) and in the response to phosphite treatment. A set of expressed genes associated with innate resistance was found to overlap with an expressed gene set for phosphite-induced resistance. This observation may indicate that phosphite treatment increases the resistance of susceptible host plants. In addition, genes of the pathogen involved in detoxification were upregulated in phosphite-treated plants compared to phosphite-untreated plants. In summary, our RNA-Seq analysis supports a two-fold mode of action of phosphites, including a direct toxic effect on P. ramorum and an indirect enhancement of resistance in the tanoak host.

Nano-Elicitation as an Effective and Emerging Strategy for In Vitro Production of Industrially Important Flavonoids

Flavonoids represent a popular class of industrially important bioactive compounds. They possess valuable health-benefiting and disease preventing properties, and therefore they are an important component of the pharmaceutical, nutraceutical, cosmetical and medicinal industries. Moreover, flavonoids possess significant antiallergic, antihepatotoxic, anti-inflammatory, antioxidant, antitumor, antiviral, and antibacterial as well as cardio-protective activities. Due to these properties, there is a rise in global demand for flavonoids, forming a significant part of the world market. However, obtaining flavonoids directly from plants has some limitations, such as low quantity, poor extraction, over-exploitation, time consuming process and loss of flora. Henceforth, there is a shift towards the in vitro production of flavonoids using the plant tissue culture technique to achieve better yields in less time. In order to achieve the productivity of flavonoids at an industrially competitive level, elicitation is a useful tool. The elicitation of in vitro cultures induces stressful conditions to plants, activates the plant defense system and enhances the accumulation of secondary metabolites in higher quantities. In this regard, nanoparticles (NPs) have emerged as novel and effective elicitors for enhancing the in vitro production of industrially important flavonoids. Different classes of NPs, including metallic NPs (silver and copper), metallic oxide NPs (copper oxide, iron oxide, zinc oxide, silicon dioxide) and carbon nanotubes, are widely reported as nano-elicitors of flavonoids discussed herein. Lastly, the mechanisms of NPs as well as knowledge gaps in the area of the nano-elicitation of flavonoids have been highlighted in this review.

Iron Complexes of Flavonoids-Antioxidant Capacity and Beyond

Flavonoids are common plant natural products able to suppress ROS-related damage and alleviate oxidative stress. One of key mechanisms, involved in this phenomenon is chelation of transition metal ions. From a physiological perspective, iron is the most significant transition metal, because of its abundance in living organisms and ubiquitous involvement in redox processes. The chemical, pharmaceutical, and biological properties of flavonoids can be significantly affected by their interaction with transition metal ions, mainly iron. In this review, we explain the interaction of various flavonoid structures with Fe(II) and Fe(III) ions and critically discuss the influence of chelated ions on the flavonoid biochemical properties. In addition, specific biological effects of their iron metallocomplexes, such as the inhibition of iron-containing enzymes, have been included in this review.

A comparative theoretical mechanism on simplified flavonoid derivatives and isoxazolone analogous as Michael system inhibitor

Flavonoids are a big class of natural product and have a wide range of biological activities. Some of these applications depend on its antioxidant capacity. Nevertheless, another mechanism can be involved by means of alkylation reaction on α,β-unsaturated carbonyl system. This study aimed to evaluate the antioxidant capacity and the chemical reactivity among simplified flavonoid derivatives and isoxazolone analogous as Michael system by using B3LYP functional and 6-311 g(d,p) basis set. Frontier molecular orbital, ionization potential (IP), spin density contributions, and Fukui index explain the antioxidant capacity and reactivity index on isoxazolone and its related derivatives. The best contribution at β-alkene moiety is related to better reactivity of α,β-unsaturated carbonyl group. A decrease in antioxidant capacity is related to an increase in the chemical reactivity index. The frontier molecular orbitals show that aurone is more reactive than isoxazolone. In accordance with Fukui index, isoxazolone can be better inhibitor as Michael system when compared to flavonoid derivatives. Graphical abstract.

A Tissue-Specific Landscape of Alternative Polyadenylation, lncRNAs, TFs, and Gene Co-expression Networks in Liriodendron chinense

Liriodendron chinense is an economically and ecologically important deciduous tree species. Although the reference genome has been revealed, alternative polyadenylation (APA), transcription factors (TFs), long non-coding RNAs (lncRNAs), and co-expression networks of tissue-specific genes remain incompletely annotated. In this study, we used the bracts, petals, sepals, stamens, pistils, leaves, and shoot apex of L. chinense as materials for hybrid sequencing. On the one hand, we improved the annotation of the genome. We detected 13,139 novel genes, 7,527 lncRNAs, 1,791 TFs, and 6,721 genes with APA sites. On the other hand, we found that tissue-specific genes play a significant role in maintaining tissue characteristics. In total, 2,040 tissue-specific genes were identified, among which 9.2% of tissue-specific genes were affected by APA, and 1,809 tissue-specific genes were represented in seven specific co-expression modules. We also found that bract-specific hub genes were associated plant defense, leaf-specific hub genes were involved in energy metabolism. Moreover, we also found that a stamen-specific hub TF Lchi25777 may be involved in the determination of stamen identity, and a shoot-apex-specific hub TF Lchi05072 may participate in maintaining meristem characteristic. Our study provides a landscape of APA, lncRNAs, TFs, and tissue-specific gene co-expression networks in L. chinense that will improve genome annotation, strengthen our understanding of transcriptome complexity, and drive further research into the regulatory mechanisms of tissue-specific genes.

Molecular investigation of Tuscan sweet cherries sampled over three years: gene expression analysis coupled to metabolomics and proteomics

Sweet cherry (Prunus avium L.) is a stone fruit widely consumed and appreciated for its organoleptic properties, as well as its nutraceutical potential. We here investigated the characteristics of six non-commercial Tuscan varieties of sweet cherry maintained at the Regional Germplasm Bank of the CNR-IBE in Follonica (Italy) and sampled ca. 60 days post-anthesis over three consecutive years (2016-2017-2018). We adopted an approach merging genotyping and targeted gene expression profiling with metabolomics. To complement the data, a study of the soluble proteomes was also performed on two varieties showing the highest content of flavonoids. Metabolomics identified the presence of flavanols and proanthocyanidins in highest abundance in the varieties Morellona and Crognola, while gene expression revealed that some differences were present in genes involved in the phenylpropanoid pathway during the 3 years and among the varieties. Finally, proteomics on Morellona and Crognola showed variations in proteins involved in stress response, primary metabolism and cell wall expansion. To the best of our knowledge, this is the first multi-pronged study focused on Tuscan sweet cherry varieties providing insights into the differential abundance of genes, proteins and metabolites.

A Metabolomic Landscape of Maize Plants Treated With a Microbial Biostimulant Under Well-Watered and Drought Conditions

Microbial plant biostimulants have been successfully applied to improve plant growth, stress resilience and productivity. However, the mechanisms of action of biostimulants are still enigmatic, which is the main bottleneck for the fully realization and implementation of biostimulants into the agricultural industry. Here, we report the elucidation of a global metabolic landscape of maize (Zea mays L) leaves in response to a microbial biostimulant, under well-watered and drought conditions. The study reveals that the increased pool of tricarboxylic acid (TCA) intermediates, alterations in amino acid levels and differential changes in phenolics and lipids are key metabolic signatures induced by the application of the microbial-based biostimulant. These reconfigurations of metabolism gravitate toward growth-promotion and defense preconditioning of the plant. Furthermore, the application of microbial biostimulant conferred enhanced drought resilience to maize plants via altering key metabolic pathways involved in drought resistance mechanisms such as the redox homeostasis, strengthening of the plant cell wall, osmoregulation, energy production and membrane remodeling. For the first time, we show key molecular events, metabolic reprogramming, activated by a microbial biostimulant for plant growth promotion and defense priming. Thus, these elucidated metabolomic insights contribute to ongoing efforts in decoding modes of action of biostimulants and generating fundamental scientific knowledgebase that is necessary for the development of the plant biostimulants industry, for sustainable food security.

A Review of the Role of Flavonoids in Peptic Ulcer (2010-2020)

Peptic ulcers are characterized by erosions on the mucosa of the gastrointestinal tract that may reach the muscle layer. Their etiology is multifactorial and occurs when the balance between offensive and protective factors of the mucosa is disturbed. Peptic ulcers represent a global health problem, affecting millions of people worldwide and showing high rates of recurrence. Helicobacter pylori infection and the use of non-steroidal anti-inflammatory drugs (NSAIDs) are one of the most important predisposing factors for the development of peptic ulcers. Therefore, new approaches to complementary treatments are needed to prevent the development of ulcers and their recurrence. Natural products such as medicinal plants and their isolated compounds have been widely used in experimental models of peptic ulcers. Flavonoids are among the molecules of greatest interest in biological assays due to their anti-inflammatory and antioxidant properties. The present study is a literature review of flavonoids that have been reported to show peptic ulcer activity in experimental models. Studies published from January 2010 to January 2020 were selected from reference databases. This review refers to a collection of flavonoids with antiulcer activity in vivo and in vitro models.

A Phytochemical Perspective on Plant Defense Against Nematodes

Given the large yield losses attributed to plant-parasitic nematodes and the limited availability of sustainable control strategies, new plant-parasitic nematode control strategies are urgently needed. To defend themselves against nematode attack, plants possess sophisticated multi-layered immune systems. One element of plant immunity against nematodes is the production of small molecules with anti-nematode activity, either constitutively or after nematode infection. This review provides an overview of such metabolites that have been identified to date and groups them by chemical class (e.g., terpenoids, flavonoids, glucosinolates, etc.). Furthermore, this review discusses strategies that have been used to identify such metabolites and highlights the ways in which studying anti-nematode metabolites might be of use to agriculture and crop protection. Particular attention is given to emerging, high-throughput approaches for the identification of anti-nematode metabolites, in particular the use of untargeted metabolomics techniques based on nuclear magnetic resonance (NMR) and mass spectrometry (MS).

Chemical responses of an invasive plant to herbivory and abiotic environments reveal a novel invasion mechanism

Invasive plant environments differ along latitudes and between native and introduced ranges. In response to herbivory and abiotic stresses that vary with latitudes and between ranges, invasive plants may shift their secondary chemicals to facilitate invasion success. However, it remains unclear whether and how invasive plant chemical responses to herbivory and chemical responses to abiotic environments are associated. We conducted large scale field surveys of herbivory on the invasive tallow tree (Triadica sebifera) along latitudes in both its native (China) and introduced ranges (United States) and collected leaf samples for analyses of tannins and flavonoids. We used data on climate and solar radiation to examine these chemical responses to abiotic environments and their variations along these latitudes and between ranges. We also re-analyzed previously published data from multiple common garden experiments on tallow tree to investigate genetic divergence of secondary chemical concentrations between introduced and native populations. We found foliar tannins and herbivory (chewing, sucking) were higher in the native range compared to the invasive range. Allocation to tannins versus flavonoids decreased with latitude in the native range but did not vary in the invasive range. Analyses of previously published common garden experimental data indicated genetic divergence contributes to chemical concentration differences between ranges. Our field data further indicated that the latitudinal patterns were primarily phenotypic responses to herbivory in China while in US they were primarily phenotypic responses to abiotic environments. The variation of tannins may be linked to flavonoids, given tannins and flavonoids share a biosynthesis pathway. Together, our results suggest that invasive plants adjust their secondary metabolism to decrease chemicals that primarily defend against herbivory and increase those that help them to respond to their abiotic environment. These findings deepen our understanding of how invasive plants adapt to biogeographically heterogeneous environments through trade-offs between secondary chemical responses.

Discovery of novel potential plant growth regulators from Corydalis mucronifera

Three pairs of enantiomers mucroniferals A-C (1-3), with a novel skeleton of 1,4-epoxynaphthalene-2,3-dicarboxylic acid first reported from nature source, were isolated from Corydalis mucronifera. Their structures were elucidated based on extensive spectroscopic data analysis of MS, 1D and 2D NMR, and their absolute configurations were confirmed by single-crystal X-ray diffraction analysis and comparison of the experimental and calculated ECD data. Mucroniferals A-C showed broad-spectrum inhibitory activities on seedling growth of all plants tested (Lepidium apetalum, Raphanus sativus, Lactuca sativa, and Arabidopsis thaliana) with a dose-dependent relationship. Additionally, mucroniferals A and B exhibited significant inhibitory effects on germination of most seeds at concentration of 80 μg/mL, and the inhibition was reversible.

Profiling of Altered Metabolomic States in Bidens pilosa Leaves in Response to Treatment by Methyl Jasmonate and Methyl Salicylate

Bidens pilosa (Asteraceae) is an edible medicinal plant with many bioactivities reported to have a health-beneficial role in controling various diseases. Though B. pilosa contain a diverse array of natural products, these are produced in relatively low concentrations. A possible way to enhance secondary metabolite production can be through the use of elicitors. Here, the effects of exogenous treatments with two signal molecules—methyl jasmonate (MeJA) and methyl salicylate (MeSA)—on the metabolomic profiles of B. pilosa leaves were investigated. Plants were treated with 0.5 mM of MeJA or MeSA and harvested at 12 h and 24 h. Metabolites were extracted with methanol and separated on an ultra-high performance liquid chromatography system hyphenated to quadrupole time-of-flight mass spectrometry detection. Data was subjected to multivariate statistical analysis and modeling for annotation of metabolites. Hydroxycinnamic acid (HCA) derivatives, such as caffeoylquinic acids (CQAs), tartaric acid esters (chicoric acid and caftaric acid), chalcones, and flavonoids were identified as differentially regulated. The altered metabolomes in response to MeSA and MeJA overlapped to a certain extent, suggestive of a cross-talk between signaling and metabolic pathway activation. Moreover, the perturbation of isomeric molecules, especially the cis geometrical isomers of HCA derivatives by both treatments, further point to the biological significance of these molecules during physiological responses to stress. The results highlight the possibility of using phytohormones to enhance the accumulation of bioactive secondary metabolites in this plant.

Integrating metabolomics and targeted gene expression to uncover potential biomarkers of fungal/oomycetes-associated disease susceptibility in grapevine

Vitis vinifera, one of the most cultivated fruit crops, is susceptible to several diseases particularly caused by fungus and oomycete pathogens. In contrast, other Vitis species (American, Asian) display different degrees of tolerance/resistance to these pathogens, being widely used in breeding programs to introgress resistance traits in elite V. vinifera cultivars. Secondary metabolites are important players in plant defence responses. Therefore, the characterization of the metabolic profiles associated with disease resistance and susceptibility traits in grapevine is a promising approach to identify trait-related biomarkers. In this work, the leaf metabolic composition of eleven Vitis genotypes was analysed using an untargeted metabolomics approach. A total of 190 putative metabolites were found to discriminate resistant/partial resistant from susceptible genotypes. The biological relevance of discriminative compounds was assessed by pathway analysis. Several compounds were selected as promising biomarkers and the expression of genes coding for enzymes associated with their metabolic pathways was analysed. Reference genes for these grapevine genotypes were established for normalisation of candidate gene expression. The leucoanthocyanidin reductase 2 gene (LAR2) presented a significant increase of expression in susceptible genotypes, in accordance with catechin accumulation in this analysis group. Up to our knowledge this is the first time that metabolic constitutive biomarkers are proposed, opening new insights into plant selection on breeding programs.

Common plant flavonoids prevent the assembly of amyloid curli fibres and can interfere with bacterial biofilm formation

Like all macroorganisms, plants have to control bacterial biofilm formation on their surfaces. On the other hand, biofilms are highly tolerant against antimicrobial agents and other stresses. Consequently, biofilms are also involved in human chronic infectious diseases, which generates a strong demand for anti-biofilm agents. Therefore, we systematically explored major plant flavonoids as putative anti-biofilm agents using different types of biofilms produced by Gram-negative and Gram-positive bacteria. In Escherichia coli macrocolony biofilms, the flavone luteolin and the flavonols myricetin, morin and quercetin were found to strongly reduce the extracellular matrix. These agents directly inhibit the assembly of amyloid curli fibres by driving CsgA subunits into an off-pathway leading to SDS-insoluble oligomers. In addition, they can interfere with cellulose production by still unknown mechanisms. Submerged biofilm formation, however, is hardly affected. Moreover, the same flavonoids tend to stimulate macrocolony and submerged biofilm formation by Pseudomonas aeruginosa. For Bacillus subtilis, the flavonone naringenin and the chalcone phloretin were found to inhibit growth. Thus, plant flavonoids are not general anti-biofilm compounds but show species-specific effects. However, based on their strong and direct anti-amyloidogenic activities, distinct plant flavonoids may provide an attractive strategy to specifically combat amyloid-based biofilms of some relevant pathogens.

Deciphering the Omics of Plant-Microbe Interaction: Perspectives and New Insights

Introduction

Plants do not grow in isolation, rather they are hosts to a variety of microbes in their natural environments. While, few thrive in the plants for their own benefit, others may have a direct impact on plants in a symbiotic manner. Unraveling plant-microbe interactions is a critical component in recognizing the positive and negative impacts of microbes on plants. Also, by affecting the environment around plants, microbes may indirectly influence plants. The progress in sequencing technologies in the genomics era and several omics tools has accelerated in biological science. Studying the complex nature of plant-microbe interactions can offer several strategies to increase the productivity of plants in an environmentally friendly manner by providing better insights. This review brings forward the recent works performed in building omics strategies that decipher the interactions between plant-microbiome. At the same time, it further explores other associated mutually beneficial aspects of plant-microbe interactions such as plant growth promotion, nitrogen fixation, stress suppressions in crops and bioremediation; as well as provides better insights on metabolic interactions between microbes and plants through omics approaches. It also aims to explore advances in the study of Arabidopsis as an important avenue to serve as a baseline tool to create models that help in scrutinizing various factors that contribute to the elaborate relationship between plants and microbes. Causal relationships between plants and microbes can be established through systematic gnotobiotic experimental studies to test hypotheses on biologically derived interactions.

Conclusion

This review will cover recent advances in the study of plant-microbe interactions keeping in view the advantages of these interactions in improving nutrient uptake and plant health.

Homology modeling and molecular dynamics based insights into Chalcone synthase and Chalcone isomerase in Phyllanthus emblica L

Chalcone synthase (CHS) and chalcone isomerase (CHI) plays a major role in the biosynthesis of flavonoid in plants. In this study, we made extensive bioinformatics analysis to gain functional and structural insight into PeCHS and PeCHI proteins. The phylogenetic distribution of PeCHS and PeCHI genes encoding proteins demonstrated the close evolutionary relationship with different CHS and CHI proteins of other dicot plants. MicroRNA target analysis showed miR169n and 3p miR5053 targeting PeCHS gene while miR169c-3p and miR4248 are targeting PeCHI gene, respectively. Three-dimensional structural models of PeCHS and PeCHI proteins were elucidated by homology modeling with Ramachandran plots showing the excellent geometry of the proteins structure. Molecular docking revealed that cinnamoyl-coa and naringenin chalcone substrates are strongly bound to PeCHS and PeCHI proteins, respectively. Finally, molecular dynamics (MD) simulation for 30 ns, further yielded stability checks of ligands in the binding pocket and behavior of protein complexes. Thus MD simulation and interaction fraction analysis showed the stable conformation of PeCHS and PeCHI proteins with their respective substrates during theee simulation. Our study provides first-hand structural prospective of PeCHS and PeCHI proteins towards understanding the mechanism of flavonoid biosynthetic pathway in P. emblica.

Water Shortage Strongly Alters Formation of Calcium Oxalate Druse Crystals and Leaf Traits in Fagopyrum esculentum

Common buckwheat (Fagopyrum esculentum Moench) is a robust plant with high resistance to different environmental constraints. It contains high levels of calcium oxalate (CaOx) druse crystals, although their role remains obscure. The objective was to examine the effects of water shortage on plant biomass partition and leaf traits and formation of CaOx druse crystals in common buckwheat. Buckwheat plants were exposed to favorable and reduced water availability for 28 days. The element composition and morphological, biochemical, physiological and optical traits of the leaves, and the plant biomass were investigated under these conditions. Measurements of photochemical efficiency of photosystem II showed undisturbed functioning for buckwheat exposed to water shortage, apparently due to partially closed stomata and more efficient water regulation. Strong relationships were seen between water-related parameters and Ca, Mn and S content, and size and density of CaOx druse crystals. Redundancy analysis revealed the importance of the size of CaOx druse crystals to explain reflection in the UV range. Water shortage resulted in shorter plants with the same leaf mass (i.e., increased mass:height ratio), which, together with denser leaf tissue and higher content of photosynthetic pigments and protective substances, provides an advantage under extreme weather conditions.

Functional analysis of a novel C-glycosyltransferase in the orchid Dendrobium catenatum

Flavonoids, which are a diverse class of phytonutrients, are used by organisms to respond to nearly all abiotic stresses and are beneficial for human health. Glycosyltransferase, used during the last step of flavonoid biosynthesis, is important in flavonoid enrichment. However, little is known about glycosyltransferase in the orchid Dendrobium catenatum (D. officinale). In this study, we isolated a novel C-glycosyltransferase (designated DcaCGT) from the orchid D. catenatum by identifying and analyzing 82 putative genes in the GT1 family. DcaCGT could specifically catalyze not only di-C-glycosylation but also O-glycosylation. Apart from the normal function of catalyzing 2-hydroxynaringenin and phloretin to the respective di-C-glycosides, DcaCGT also catalyzes apigenin to cosmosiin. Targeted metabolic profiling of the substrates (2-hydroxynaringenin, phloretin, and apigenin) and products (vitexin, isovitexin, vicenin-2, nothofagin, 3',5'-di-C-glucosylphloretin, and cosmosiin) in different tissues showed that vicenin-2 was the most abundant product of this novel enzyme. Cosmosiin was detected in flowers and flower buds. We also established that DcaCGT functions expanded throughout the evolution of D. catenatum. Residual OGT activity may help D. catenatum resist drought stress. Our study illustrates the function, origin, and differentiation of DcaCGT and provides insights into glycosylation and molecular propagation processes, which can be used to improve the production of flavonoids by the cultivated medicinal plant D. catenatum.

Metabolic Profiling Provides Unique Insights to Accumulation and Biosynthesis of Key Secondary Metabolites in Annual Pasture Legumes of Mediterranean Origin

Annual legumes from the Mediterranean region are receiving attention in Australia as alternatives to traditional pasture species. The current study employed novel metabolic profiling approaches to quantify key secondary metabolites including phytoestrogens to better understand their biosynthetic regulation in a range of field-grown annual pasture legumes. In addition, total polyphenol and proanthocyanidins were quantified using Folin-Ciocalteu and vanillin assays, respectively. Metabolic profiling coupled with biochemical assay results demonstrated marked differences in the abundance of coumestans, flavonoids, polyphenols, and proanthocyanidins in annual pasture legume species. Genetically related pasture legumes segregated similarly from a chemotaxonomic perspective. A strong and positive association was observed between the concentration of phytoestrogens and upregulation of the flavonoid biosynthetic pathway in annual pasture legumes. Our findings suggest that evolutionary differences in metabolic dynamics and biosynthetic regulation of secondary metabolites have logically occurred over time in various species of annual pasture legumes resulting in enhanced plant defense.

Flavonoids and Isoflavonoids Biosynthesis in the Model Legume Lotus japonicus; Connections to Nitrogen Metabolism and Photorespiration

Phenylpropanoid metabolism represents an important metabolic pathway from which originates a wide number of secondary metabolites derived from phenylalanine or tyrosine, such as flavonoids and isoflavonoids, crucial molecules in plants implicated in a large number of biological processes. Therefore, various types of interconnection exist between different aspects of nitrogen metabolism and the biosynthesis of these compounds. For legumes, flavonoids and isoflavonoids are postulated to play pivotal roles in adaptation to their biological environments, both as defensive compounds (phytoalexins) and as chemical signals in symbiotic nitrogen fixation with rhizobia. In this paper, we summarize the recent progress made in the characterization of flavonoid and isoflavonoid biosynthetic pathways in the model legume Lotus japonicus (Regel) Larsen under different abiotic stress situations, such as drought, the impairment of photorespiration and UV-B irradiation. Emphasis is placed on results obtained using photorespiratory mutants deficient in glutamine synthetase. The results provide different types of evidence showing that an enhancement of isoflavonoid compared to standard flavonol metabolism frequently occurs in Lotus under abiotic stress conditions. The advance produced in the analysis of isoflavonoid regulatory proteins by the use of co-expression networks, particularly MYB transcription factors, is also described. The results obtained in Lotus japonicus plants can be also extrapolated to other cultivated legume species, such as soybean, of extraordinary agronomic importance with a high impact in feeding, oil production and human health.

Flavonoids repress the production of antifungal 2,4-DAPG but potentially facilitate root colonization of the rhizobacterium Pseudomonas fluorescens

In the well-known legume-rhizobia symbiosis, flavonoids released by legume roots induce expression of the Nod factors and trigger early plant responses involved in root nodulation. However, it remains largely unknown how the plant-derived flavonoids influence the physiology of non-symbiotic beneficial rhizobacteria. In this work, we demonstrated that the flavonoids apigenin and/or phloretin enhanced the swarming motility and production of cellulose and curli in Pseudomonas fluorescens 2P24, both traits of which are essential for root colonization. Using a label-free quantitative proteomics approach, we showed that apigenin and phloretin significantly reduced the biosynthesis of the antifungal metabolite 2,4-DAPG and further identified a novel flavonoid-sensing TetR regulator PhlH, which was shown to modulate 2,4-DAPG production by regulating the expression of 2,4-DAPG hydrolase PhlG. Although having similar structures, apigenin and phloretin could also influence different physiological characteristics of P. fluorescens 2P24, with apigenin decreasing the biofilm formation and phloretin inducing expression of proteins involved in the denitrification and arginine fermentation processes. Taken together, our results suggest that plant-derived flavonoids could be sensed by the TetR regulator PhlH in P. fluorescens 2P24 and acts as important signalling molecules that strengthen mutually beneficial interactions between plants and non-symbiotic beneficial rhizobacteria.

The Effect of Recombinant Tags on Citrus paradisi Flavonol-Specific 3-O Glucosyltransferase Activity

Recombinant tags are used extensively in protein expression systems to allow purification through IMAC (Immobilized Metal Affinity Chromatography), identification through Western blot, and to facilitate crystal formation for structural analysis. While widely used, their role in enzyme characterization has raised concerns with respect to potential impact on activity. In this study, a flavonol-specific 3-O glucosyltransferase (Cp3GT) from grapefruit (Citrus paradisi) was expressed in Pichia pastoris, and was assayed in its untagged form and with a C-terminal c-myc/6x His tag under various conditions to determine the effect of tags. Prior characterization of pH optima for Cp3GT obtained through expression in Escherichia coli, containing an N-terminal thioredoxin/6x His tag, indicated an optimal pH of 7-7.5, which is indicative of a normal physiological pH and agrees with other glucosyltransferase (GT) pH optima. However, characterization of Cp3GT expressed using P. pastoris with a C-terminal c-myc-6x His tag showed a higher optimal pH of 8.5-9. This suggests a possible tag effect or an effect related to physiological differences between the cell expression systems. Results testing recombinant Cp3GT expressed in Pichia with and without C-terminal tags showed a possible tag effect with regard to substrate preference and interactions with metals, but no apparent effect on enzymatic kinetics or pH optima.

Discovery of modules involved in the biosynthesis and regulation of maize phenolic compounds

Phenolic compounds are among the most diverse and widespread of specialized plant compounds and underly many important agronomic traits. Our comprehensive analysis of the maize genome unraveled new aspects of the genes involved in phenylpropanoid, monolignol, and flavonoid production in this important crop. Remarkably, just 19 genes accounted for 70 % of the overall mRNA accumulation of these genes across 95 tissues, indicating that these are the main contributors to the flux of phenolic metabolites. Eighty genes with intermediate to low expression play minor and more specialized roles. Remaining genes are likely undergoing loss of function or are expressed in limited cell types. Phylogenetic and expression analyses revealed which members of gene families governing metabolic entry and branch points exhibit duplication, subfunctionalization, or loss of function. Co-expression analysis applied to genes in sequential biosynthetic steps revealed that certain isoforms are highly co-expressed and are candidates for metabolic complexes that ensure metabolite delivery to correct cellular compartments. Co-expression of biosynthesis genes with transcription factors discovered connections that provided candidate components for regulatory modules governing this pathway. Our study provides a comprehensive analysis of maize phenylpropanoid related genes, identifies major pathway contributors, and novel candidate enzymatic and regulatory modules of the metabolic network.

Isolation and Identification of F Lavonol Glycosides from Lathyrus armenus (Boiss. & Huet)

In the last five decades study on plant secondary metabolites have been increasing. Higher plants with a wide range of secondary metabolites have been very important in the search of new therapeutic agents. In this study secondary metabolites of Lathyrus armenus (Boiss. & Huet) which are endemic in Turkey, were studied. Flavonol glycosides (Rhamnocitrin-3-O-rhamninoside, Rhamnetin-3-O-rhamninoside, Rhamnazin- 3-O-rhamninoside, kaempferol3-O-rhamninoside and, kaempferol-3-O-glucosyl (1→2) rhamnoside) were isolated by different chromatographic methods and identified by ¹H, ¹³C NMR, as well as 2D NMR and Mass spectroscopy techniques from ethyl acetate and aqueous fractions of L. armenus's methanolic extract. This is the first study about secondary metabolites of Turkish Lathyrus species.

Sub-Genome Polyploidization Effects on Metabolomic Signatures in Triploid Hybrids of Populus

Allopolyploids are known to have superior advantages such as high growth speed. Triploids have even greater heterozygosity, explaining more phenotypic variance than 2n hybrid F1 and have therefore become new resources in breeding. To date, the metabolomic basis underlying polyploidization vigor remains unclear. Here, we identified and compared 235 metabolites in the shoot apical buds between multiple allo-triploid populations and parental 2n hybrid F1 in Populus via metabolome profiling using liquid chromatography–mass spectrometry (LC–MS) assays. Associations with growth vigor in three types of allo-triploid populations, namely first division restitution (FDR), second division restitution (SDR) and postmeiotic restitution (PMR) generated from doubled 2n female gametes and male gametes of 2n hybrid, were also investigated. Each allo-triploid population has different sub-genome duplicated. Major metabolomes were amino acids, secondary metabolism associated, and carbohydrates. We mapped 181 metabolites into known metabolism pathways in the Kyoto Encyclopedia of Genes and Genomes (KEGG). Ten compounds, i.e., fructose 1,6-diphosphate and xylulose, were more abundant in all allo-triploids than the 2n hybrid. Principal component analysis revealed the abundance of metabolites fell into distinct clusters corresponding to ploidy composition. Heterozygosity in triploids mainly effected the contents of carbohydrates and secondary metabolites rather than lipids. Comparisons between subgroups with different growth rates revealed some carbohydrates and secondary metabolites of flavonoids were positively associated with gene expression and the high growth vigor. The results provided an informative metabolomic basis for factors conferring growth vigor in polyploid Populus.

Impact of Selenium and Copper Nanoparticles on Yield, Antioxidant System, and Fruit Quality of Tomato Plants

The effects of nanoparticles (NPs) on plants are contrasting; these depend on the model plant, the synthesis of the nanoparticles (concentration, size, shape), and the forms of application (foliar, substrate, seeds). For this reason, the objective of this study was to report the impact of different concentrations of selenium (Se) and copper (Cu) NPs on yield, antioxidant capacity, and quality of tomato fruit. The different concentrations of Se and Cu NPs were applied to the substrate every 15 days (five applications). The yield was determined until day 102 after the transplant. Non-enzymatic and enzymatic antioxidant compounds were determined in the leaves and fruits as well as the fruit quality at harvest. The results indicate that tomato yield was increased by up to 21% with 10 mg L-1 of Se NPs. In leaves, Se and Cu NPs increased the content of chlorophyll, vitamin C, glutathione, 2,2'-azino-bis(3-ethylbenzthiazolin-6-sulfonic acid (ABTS), superoxide dismutase (SOD), glutathione peroxidase (GPX) and phenylalanine ammonia liasa (PAL). In fruits, they increased vitamin C, glutathione, flavonoids, firmness, total soluble solids, and titratable acidity. The combination of Se and Cu NPs at optimal concentrations could be a good alternative to improve tomato yield and quality, but more studies are needed to elucidate their effects more clearly.

Research Progress of Betalain in Response to Adverse Stresses and Evolutionary Relationship Compared with Anthocyanin

Betalains are applicable to many aspects of life, and their properties, characteristics, extraction and biosynthesis process have been thoroughly studied. Although betalains are functionally similar to anthocyanins and can substitute for them to provide pigments for plant color, it is rare to study the roles of betalains in plant responses to adverse environmental conditions. Owing to their antioxidant capability to remove excess reactive oxygen species (ROS) in plants and humans, betalains have attracted much attention due to their bioactivity. In addition, betalains can also act as osmotic substances to regulate osmotic pressure in plants and play important roles in plant responses to adverse environmental conditions. The study of the physiological evolution of betalains is almost complete but remains complicated because the evolutionary relationship between betalains and anthocyanins is still uncertain. In this review, to provide a reference for the in-depth study of betalains compared with anthocyanins, the biochemical properties, biosynthesis process and roles of betalains in response to environmental stress are reviewed, and the relationship between betalains and anthocyanins is discussed.

Inhibition of CpLIP2 Lipase Hydrolytic Activity by Four Flavonols (Galangin, Kaempferol, Quercetin, Myricetin) Compared to Orlistat and Their Binding Mechanisms Studied by Quenching of Fluorescence

The inhibition of recombinant CpLIP2 lipase/acyltransferase from Candida parapsiolosis was considered a key model for novel antifungal drug discovery and a potential therapeutic target for candidiasis. Lipases have identified recently as potent virulence factors in C. parapsilosis and some other yeasts. The inhibition effects of orlistat and four flavonols (galangin, kaempferol, quercetin and myricetin) characterized by an increasing degree of hydroxylation in B-ring, were investigated using ethyl oleate hydrolysis as the model reaction. Orlistat and kaempferol (14 µM) strongly inhibited CpLIP2 catalytic activity within 1 min of pre-incubation, by 90% and 80%, respectively. The relative potency of flavonols as inhibitors was: kaempferol > quercetin > myricetin > galangin. The results suggested that orlistat bound to the catalytic site while kaempferol interacted with W294 on the protein lid. A static mechanism of interactions between flavonols and CpLIP2 lipase was confirmed by fluorescence quenching analyses, indicating that the interactions were mainly driven by hydrophobic bonds and electrostatic forces. From the Lehrer equation, fractions of tryptophan accessibility to the quencher were evaluated, and a relationship with the calculated number of binding sites was suggested.