Flavonoid gene expression and UV photoprotection in transgenic and mutant Petunia leaves

The effect of plant growth regulators, FeO3-CTs nanoparticles and LEDs light on the growth and biochemical compounds of black seed (Nigella sativa L.) callus in vitro

BACKGROUND

black seed (Nigella sativa L.) has long been utilized in traditional medicine and as a food ingredient due to its potential therapeutic properties including its effectiveness against cancer, coronaviruses, and bacterial infections. Recently, it has garnered significant attention for its rich reservoir of beneficial secondary metabolites. In vitro culture of black seeds presents an efficient and modern approach for the large-scale production of these valuable compounds, offering advantages such as space efficiency, reduced time, and lower costs. This study aimed to develop and optimize a protocol for callus induction and the identification of key secondary metabolites, including thymoquinone (TQ), phenolic compounds, and flavonoids. To induce callus formation in seed explants, two plant growth regulators (PGRs) were applied individually or in combination and incorporated into Murashige and Skoog (MS) culture medium.

RESULTS

The combination of Auxin, 2,4-dichlorophenoxyacetic acid (2,4-D) and cytokinin, 6-benzylaminopurine (BAP), effectively induced callus formation in most explants, with the response varying based on concentration. The highest callus fresh weight (7.02 g) was obtained on Red(R) LED lighting with FeO3-CTs nanoparticles (100 mg/L- 1), which also resulted in the highest dry weight (1.307 g) after 40 days of cultivation. Similarly, the highest levels of phenols, flavonoids and amino acids were observed under R LED with FeO3-CTs nanoparticles (100 mg L- 1), while FeO3-CTs nanoparticles at 100 and 200 mg/L- 1) exhibited significant effects on metabolite production. In contrast, the antioxidant activity against DPPH free radicals and total carbohydrate accumulation were enhanced in callus cultures treated with FeO3-CTs nanoparticles (200 mg/L- 1) under dark conditions. Additionally, GC-MS analysis revealed that FeO3-CTs nanoparticles (100 mg/L- 1) yielded the most effective enhancement of secondary metabolites under blue (B) LED light at a concentration of 295 mg/L- 1.

CONCLUSION

The finding of this study highlights the potential of the proposed method for the large-scale production of secondary metabolites, total carbohydrates, amino acids, phenolic compounds, and flavonoids from black seed callus cultures in a controlled environment. This optimized approach offers a cost-effective and space-efficient strategy for enhancing bioactive compound synthesis, with potential applications in pharmaceutical and nutraceutical industries.

Flood-Induced Insect Resistance in Maize Involves Flavonoid-Dependent Salicylic Acid Induction

Plants have evolved the ability to respond to a diverse range of biotic and abiotic stresses. Often, combining these stresses multiplies the challenge for the plants, but occasionally the combined stress can induce unexpected synergistic defences. In maize, combined flooding and herbivory induces a salicylic acid (SA)-dependent defence against Spodoptera frugiperda (fall armyworm). In this study we used RNAseq and metabolic profiling to show that flavonoids are involved in maize response to combined flooding and herbivory. To assess the role of flavonoids in flood-induced S. frugiperda resistance, we analyzed the maize idf mutant that has compromised expression of chalcone synthase, the first enzyme in flavonoid biosynthesis. This flavonoid-deficient mutant was compromised both in flood-induced S. frugiperda resistance and in SA accumulation. These data revealed an unexpected requirement for flavonoids in SA induction. In contrast to idf, the flavonoid 3' hydroxylase mutant, pr1, showed enhanced SA accumulation after combinatorial treatment, which closely correlated with elevated levels of select flavonoids and the dihydroflavonol reductase, anthocyaninless1 (a1) mutant, was unaffected in its SA-induction. These data indicate that specific flavonoids likely play a role in flood-induced SA accumulation and S. frugiperda resistance.

Repressor MrERF4 and Activator MrERF34 Synergistically Regulate High Flavonol Accumulation Under UV-B Irradiation in Morella rubra Leaves

Flavonols are important plant photoprotectants to defence UV-B irradiation, however, the underlying transcriptional regulatory mechanism of rapid flavonol accumulation in response to UV-B remains unknown. In this study, content of flavonols was significantly induced from 0.11 to 3.80 mg/g fresh weight by UV-B irradiation in leaves of Morella rubra seedlings. MrERF34 was identified as an activator that can regulate the expression of MrFLS2, and promoted flavonol biosynthesis with activator MrMYB12 under UV-B treatment. Transient overexpression of MrERF34 resulted in higher flavonol accumulation, while virus-induced gene silencing of MrERF34 reduced the content of flavonols in bayberry leaves. We further demonstrated that a repressor MrERF4 inhibited the expression of MrERF34 and MrMYB12 as well as MrFLS2 via ERF-associated-amphiphilic repression motif. Exposure to UV-B reduced the promoter activity and transcription of MrERF4, which weakened the inhibitory effect of MrERF4 on MrERF34, MrMYB12, and MrFLS2, leading to a tremendous accumulation of flavonols. Such inhibitory roles of MrERF4 in regulation of flavonol biosynthesis were further validated by transient overexpression in leaves of Nicotiana benthamiana and M. rubra. These findings enrich the synergistical regulatory mechanisms between repressor and activators in flavonol biosynthesis, and provide new insights into photoprotectants biosynthesis to mitigate UV-B stress in plants.

Proteomic and metabolomic insights into the impact of topping treatment on cigar tobacco

Top removal is a widely utilized method in production process of tobacco, but little is known regarding the way it impacts protein and metabolic regulation. In this study, we investigated the underlying processes of alterations in cigar tobacco leaves with and without top removal, using a combined proteomic and metabolomic approach. The results revealed that: (1) Topping significantly affected superoxide anion (O2 -) levels, superoxide dismutase (SOD) activity, and malondialdehyde (MDA) content, (2) In the cigar tobacco proteome, 385 differentially expressed proteins (DEPs) were identified, with 228 proteins upregulated and 156 downregulated. Key pathways enriched included flavonoid biosynthesis, porphyrin and chlorophyll metabolism, cysteine and methionine metabolism, and amino acid biosynthesis and metabolism. A network of 161 nodes interconnected by 102 significantly altered proteins was established, (3) In the cigar tobacco metabolome, 247 significantly different metabolites (DEMs) were identified, with 120 upregulated and 128 downregulated metabolites, mainly comprising lipids and lipid-like molecules, phenylpropanoids and polyketides, organic acids and derivatives, and organic heterocyclic compounds, (4) KEGG pathway enrichment revealed upregulation of proteins such as chalcone synthase (CHS), chalcone isomerase (CHI), naringenin 3-dioxygenase (F3H), and flavonoid 3'-monooxygenase (F3'H), along with metabolites like pinocembrin, kaempferol, trifolin, rutin, and quercetin, enhancing the pathways of 'flavonoid' and 'flavone and flavonol' biosynthesis. This study sheds light on the metabolic and proteomic responses of cigar tobacco after topping.

Ultraviolet-A Radiation (UVA) as a Stress and the Influence of Provenance and Leaf Age on the Expression of Phenolic Compounds by Eucalyptus camaldulensis ssp. camaldulensis

Ultraviolet radiation (UV) represents a significant abiotic stress, affecting green plants. Phenolic compounds have been suggested as components involved in plant photoprotective adaptation. We used a unique combination of experimental (LED lighting and leaf tagging) and analytical (unbiased, or untargeted, metabolomics) approaches to study the effects of high (approximating mid-summer) and low (approximating winter) levels of UVA on the expression of phenolic compounds. These consisted of river red gum (Eucalyptus camaldulensis ssp. camaldulensis) of five provenances. The geographically separated provenances used in our study spanned the lowest and highest latitudes of the range of this subspecies. The concentrations of gallotannins and ellagitannins (i.e., hydrolysable tannins) increased most under high levels of UVA, but responses only differed slightly among provenances. The most substantial changes in the composition of phenolic compounds were associated with leaf age. Overall, 3-month-old (herein, termed 'young') leaves had substantially different phenolic compositions to 6- and 12-month-old ('old') leaves. Hydrolysable tannins were more abundant in young leaves, whereas pedunculagin, catechin, and kaempferol galloyl glucoses were more abundant in old leaves. High levels of UVA altered the expression of phenolic compounds, but our experimental saplings were unlikely to experience photoinhibition because they were not exposed to high levels of light and low temperatures, nor were they nitrogen-limited. We expect that changes in phenolic compounds would have been more pronounced if we had induced photoinhibition.

MdFC2, a ferrochelatase gene, is a positive regulator of ALA-induced anthocyanin accumulation in apples

5-Aminolevulinic acid (ALA), a key biosynthetic precursor of tetrapyrrole compounds, significantly induces anthocyanin accumulation in apple (Malus × domestica Borkh.) as well as other fruits. Although the molecular mechanisms of ALA-induced anthocyanin accumulation have been reported, it remains unknown whether the metabolism of ALA is involved in ALA-induced anthocyanin accumulation. Here, we found that MdFC2, a gene encoding ferrochelatase (MdFC2), which catalyzes the generation of heme from protoporphyrin lX (PPIX), may play an important role in ALA-induced apple anthocyanin accumulation. Exogenous ALA induced the MdFC2 expression as well as anthocyanin accumulation in apple leaves, calli, and isolated fruits. MdFC2 overexpression in apple leaves or calli significantly enhanced anthocyanin accumulation as well as the expression of genes involved in anthocyanin biosynthesis, while RNA interference MdFC2 inhibited anthocyanin accumulation and the expression of genes involved in anthocyanin biosynthesis. When 2,2'-dithiodipyridine, an inhibitor of MdFC2, was added, ALA-induced anthocyanin accumulation was blocked. These results suggest that ALA-induced anthocyanin accumulation of apple may be regulated by heme or its biosynthesis, among which MdFC2 or MdFC2 may play a critical positive regulatory role. This finding provides a novel insight to explore the mechanisms of ALA-regulating physiological processes and better application of ALA in high-quality fruit production.

Ultrastructure and development of the floral nectary from Borago officinalis L. and phytochemical changes in its secretion

Although Boraginaceae have been classified as good sources of nectar for many insects, little is still known about their nectar and nectaries. Thus, in the present contribution, we investigated the nectar production dynamics and chemistry in Borago officinalis L. (borage or starflower), together with its potential interaction capacity with pollinators. A peak of nectar secretion (∼5.1 µL per flower) was recorded at anthesis, to decrease linearly during the following 9 days. In addition, TEM and SEM analyses were performed to understand ultrastructure and morphological changes occurring in borage nectary before and after anthesis, but also after its secretory phase. Evidence suggested that nectar was transported by the apoplastic route (mainly from parenchyma to epidermis) and then released essentially by exocytotic processes, that is a granulocrine secretion. This theory was corroborated by monitoring the signal of complex polysaccharides and calcium, respectively, via Thiéry staining and ESI/EELS technique. After the secretory phase, nectary underwent degeneration, probably through autophagic events and/or senescence induction. Furthermore, nectar (Nec) and other flower structures (i.e., sepals, gynoecia with nectaries, and petals) from borage were characterized by spectrophotometry and HPLC-DAD, in terms of plant secondary metabolites, both at early (E-) and late (L-) phase from anthesis. The content of phytochemicals was quantified and discussed for all samples, highlighting potential biological roles of these compounds in the borage flower (e.g., antimicrobial, antioxidant, staining effects). Surprisingly, a high significant accumulation of flavonoids was registered in L-Nec, with respect to E-Nec, indicating that this phenomenon might be functional and able to hide molecular (e.g., defence against pathogens) and/or ecological (e.g., last call for pollinators) purposes. Indeed, it is known that these plant metabolites influence nectar palatability, encouraging the approach of specialist pollinators, deterring nectar robbers, and altering the behaviour of insects.

Transcription factor MdNAC33 is involved in ALA-induced anthocyanin accumulation in apples

5-Aminolevulinic acid (ALA), as a new natural plant growth regulator, has a significant function in promoting anthocyanin accumulation in many species of fruits. However, the mechanisms underlying remain obscure. In a transcriptome study of our group, it was found that many transcription factors (TFs) including NACs responsive to ALA treatment during anthocyanin accumulation. In the present study, we found a NAC of apple, MdNAC33 was coordinatively expressed with anthocyanin accumulation after ALA treatment in the apple fruits and leaves, suggesting that this TF may be involved in anthocyanin accumulation induced by ALA. We found that the MdNAC33 protein was localized in the nucleus and exhibited strong transcriptional activity in both yeast cells and plants, where its C-terminal contributed to the transcriptional activity. Functional analysis showed that overexpression of MdNAC33 promoted the accumulation of anthocyanin, while the silencing vector of MdNAC33 (RNAi) significantly impaired the anthocyanin accumulation induced by ALA. Yeast one-hybrid (Y1H), luciferase assay and electrophoretic mobility shift assay (EMSA) indicated that MdNAC33 could bind to promoters of MdbHLH3, MdDFR and MdANS to activate the gene expressions. In addition, MdNAC33 specifically interacts with MdMYB1, a positive regulator of anthocyanin biosynthesis, which was then in turn binding to its target genes MdUFGT and MdGSTF12, to promote anthocyanin accumulation in apples. Taken together, our data indicate that MdNAC33 plays multiple roles in ALA-induced anthocyanin biosynthesis. It provides new insights into the mechanisms of anthocyanin accumulation induced by ALA.

Effects of light spectra on morphological characteristics, primary and specialized metabolites of Thymus vulgaris L

Light is a crucial environmental factor that profoundly influences the growth and development of plants. However, the precise mechanisms by which light affects biochemical processes and growth and development factors in Thymus vulgaris remain unknown, necessitating further investigation. Hence, this study aimed to investigate the impact of different light spectra, including red, blue, red-blue, and white lights, on the morphological characteristics, primary, and specialized metabolites of T. vulgaris. Compared to white light, red light significantly increased leaf area (by 64 %), the number of branches (by 132 %), and dry weight (by 6.2 %), although a 40 % reduction in fresh weight was observed under red light conditions. Red-blue light notably enhanced canopy width, fresh weight, and dry weight. Gas chromatography/mass spectrometry (GC/MS) analysis of the plant's essential oil (EO) revealed that p-Cymene and γ-Terpinene were present at the highest levels. Notably, p-Cymene exhibited the highest concentrations under white light and blue light treatments, reaching 60.92 % and 59.53 %, respectively. Moreover, under the same light conditions, phenol and antioxidant levels were significantly elevated. Overall, these findings indicate that red and red-blue light spectra are the most favorable for thyme production.

Rhododendron chrysanthum's Primary Metabolites Are Converted to Phenolics More Quickly When Exposed to UV-B Radiation

The plant defense system is immediately triggered by UV-B irradiation, particularly the production of metabolites and enzymes involved in the UV-B response. Although substantial research on UV-B-related molecular responses in Arabidopsis has been conducted, comparatively few studies have examined the precise consequences of direct UV-B treatment on R. chrysanthum. The ultra-high-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) methodology and TMT quantitative proteomics are used in this study to describe the metabolic response of R. chrysanthum to UV-B radiation and annotate the response mechanism of the primary metabolism and phenolic metabolism of R. chrysanthum. The outcomes demonstrated that following UV-B radiation, the primary metabolites (L-phenylalanine and D-lactose*) underwent considerable changes to varying degrees. This gives a solid theoretical foundation for investigating the use of precursor substances, such as phenylalanine, to aid plants in overcoming abiotic stressors. The external application of ABA produced a considerable increase in the phenolic content and improved the plants' resistance to UV-B damage. Our hypothesis is that externally applied ABA may work in concert with UV-B to facilitate the transformation of primary metabolites into phenolic compounds. This hypothesis offers a framework for investigating how ABA can increase a plant's phenolic content in order to help the plant withstand abiotic stressors. Overall, this study revealed alterations and mechanisms of primary and secondary metabolic strategies in response to UV-B radiation.

Uncovering nutritional metabolites and candidate genes involved in flavonoid metabolism in Houttuynia cordata through combined metabolomic and transcriptomic analyses

The perennial herb Houttuynia cordata has long been cultivated and used as medicinal and edible plant in Asia. Nowadays, increasing attention is attracted due to its numerous health benefits. Flavonoids are the main chemical constituents exerting pharmacological activities. In the present study, we investigated both metabolome and transcriptome of two H. cordata accessions (6# and 7#) with distinct flavonoids contents. In total 397 metabolites, i.e., 220 flavonoids, 92 amino acids and derivatives, 20 vitamins, and 65 saccharides were abundant in aboveground part. Cyanidin-3-O-rutinoside and quercetin-3-O-galactoside were the most abundant flavonoids, which can be categorized into seven classes, namely anthocyanidins, chalcones, flavanols, flavanones, flavanonols, flavones, and flavonols. Flavonols was the most abundant group. Contents of 112 flavonoids differed significantly between the two accessions, with catechin-(7,8-bc)-4α-(3,4-dihydroxyphenyl)-dihydro-2-(3H)-one, cinchonain Id, and cinchonain Ic being the dominant flavonoid metabolites among them. Pinocembrin-7-O-neohesperidoside, pinocembrin-7-O-rutinoside, and kaempferol-3-O-galactoside-4'-O-glucoside were uniquely abundant in accession 7. Transcriptome data revealed a total of 110 different expressed genes related to flavonoid metabolism, with more highly expressed genes observed in 7#. We annotated a total of 19 differential flavonoid metabolites and 34 differentially expressed genes that are associated with the flavonoid metabolic network. Based on the transcriptome and qPCR data a total of 8 key candidate genes involved in flavonoid metabolism were identified. The ANS gene were found to play an important role in the synthesis of cyanidin-3-O-glucoside, while the CHI, F3'H and FLS genes were mainly responsible for controlling the levels of flavanones, flavones, and flavonols, respectively. Collectively, the present study provides important insights into the molecular mechanism underlying flavonoid metabolism in H. cordata.

Magnesium Nutrient Application Induces Metabolomics and Physiological Responses in Mulberry (Morus alba) Plants

Mulberry (Morus alba) is a significant plant with numerous economic benefits; however, its growth and development are affected by nutrient levels. A high level of magnesium (Mg) or magnesium nutrient starvation are two of the significant Mg factors affecting plant growth and development. Nevertheless, M. alba's metabolic response to different Mg concentrations is unclear. In this study, different Mg concentrations, optimal (3 mmol/L), high (6 mmol/L and 9 mmol/L), or low (1 and 2 mmol/L) and deficient (0 mmol/L), were applied to M. alba for three weeks to evaluate their effects via physiological and metabolomics (untargeted; liquid chromatography-mass spectrometry (LC-MS)) studies. Several measured physiological traits revealed that Mg deficiency and excess Mg altered net photosynthesis, chlorophyll content, leaf Mg content and fresh weight, leading to remarkable reductions in the photosynthetic efficiency and biomass of mulberry plants. Our study reveals that an adequate supply of the nutrient Mg promoted the mulberry's physiological response parameters (net photosynthesis, chlorophyll content, leaf and root Mg content and biomass). The metabolomics data show that different Mg concentrations affect several differential metabolite expressions (DEMs), particularly fatty acyls, flavonoids, amino acids, organic acid, organooxygen compounds, prenol lipids, coumarins, steroids and steroid derivatives, cinnamic acids and derivatives. An excessive supply of Mg produced more DEMs, but negatively affected biomass production compared to low and optimum supplies of Mg. The significant DEMs correlated positively with mulberry's net photosynthesis, chlorophyll content, leaf Mg content and fresh weight. The mulberry plant's response to the application of Mg used metabolites, mainly amino acids, organic acids, fatty acyls, flavonoids and prenol lipids, in the KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways. These classes of compounds were mainly involved in lipid metabolism, amino acid metabolism, energy metabolism, the biosynthesis of other secondary metabolites, the biosynthesis of other amino acids, the metabolism of cofactors and vitamin pathways, indicating that mulberry plants respond to Mg concentrations by producing a divergent metabolism. The supply of Mg nutrition was an important factor influencing the induction of DEMs, and these metabolites were critical in several metabolic pathways related to magnesium nutrition. This study provides a fundamental understanding of DEMs in M. alba's response to Mg nutrition and the metabolic mechanisms involved, which may be critical to the mulberry genetic breeding program.

Natural flavonols: actions, mechanisms, and potential therapeutic utility for various diseases

Background

Flavonols are phytoconstituents of biological and medicinal importance. In addition to functioning as antioxidants, flavonols may play a role in antagonizing diabetes, cancer, cardiovascular disease, and viral and bacterial diseases. Quercetin, myricetin, kaempferol, and fisetin are the major dietary flavonols. Quercetin is a potent scavenger of free radicals, providing protection from free radical damage and oxidation-associated diseases.

Main body of the abstract

An extensive literature review of specific databases (e.g., Pubmed, google scholar, science direct) were conducted using the keywords "flavonol," "quercetin," "antidiabetic," "antiviral," "anticancer," and "myricetin." Some studies concluded that quercetin is a promising antioxidant agent while kaempferol could be effective against human gastric cancer. In addition, kaempferol prevents apoptosis of pancreatic beta-cells via boosting the function and survival rate of the beta-cells, leading to increased insulin secretion. Flavonols also show potential as alternatives to conventional antibiotics, restricting viral infection by antagonizing the envelope proteins to block viral entry.

Short conclusion

There is substantial scientific evidence that high consumption of flavonols is associated with reduced risk of cancer and coronary diseases, free radical damage alleviation, tumor growth prevention, and insulin secretion improvement, among other diverse health benefits. Nevertheless, more studies are required to determine the appropriate dietary concentration, dose, and type of flavonol for a particular condition to prevent any adverse side effects.

Unique gene duplications and conserved microsynteny potentially associated with resistance to wood decay in the Lauraceae

Wood decay resistance (WDR) is marking the value of wood utilization. Many trees of the Lauraceae have exceptional WDR, as evidenced by their use in ancient royal palace buildings in China. However, the genetics of WDR remain elusive. Here, through comparative genomics, we revealed the unique characteristics related to the high WDR in Lauraceae trees. We present a 1.27-Gb chromosome-level assembly for Lindera megaphylla (Lauraceae). Comparative genomics integrating major groups of angiosperm revealed Lauraceae species have extensively shared gene microsynteny associated with the biosynthesis of specialized metabolites such as isoquinoline alkaloids, flavonoid, lignins and terpenoid, which play significant roles in WDR. In Lauraceae genomes, tandem and proximal duplications (TD/PD) significantly expanded the coding space of key enzymes of biosynthesis pathways related to WDR, which may enhance the decay resistance of wood by increasing the accumulation of these compounds. Among Lauraceae species, genes of WDR-related biosynthesis pathways showed remarkable expansion by TD/PD and conveyed unique and conserved motifs in their promoter and protein sequences, suggesting conserved gene collinearity, gene expansion and gene regulation supporting the high WDR. Our study thus reveals genomic profiles related to biochemical transitions among major plant groups and the genomic basis of WDR in the Lauraceae.

Tree tobacco (Nicotiana glauca) cuticular wax composition is essential for leaf retention during drought, facilitating a speedy recovery following rewatering

Despite decades of extensive study, the role of cuticular lipids in sustaining plant fitness is far from being understood. We utilized genome-edited tree tobacco (Nicotiana glauca) to investigate the significance of different classes of epicuticular wax in abiotic stress such as cuticular water loss, drought, and light response. We generated mutants displaying a range of wax compositions. Four wax mutants and one cutin mutant were extensively investigated for alterations in their response to abiotic factors. Although the mutations led to elevated cuticular water loss, the wax mutants did not display elevated transpiration or reduced growth under nonstressed conditions. However, under drought, plants lacking alkanes were unable to reduce their transpiration, leading to leaf death, impaired recovery, and stem cracking. By contrast, plants deficient in fatty alcohols exhibited elevated drought tolerance, which was part of a larger trend of plant phenotypes not clustering by a glossy/glaucous appearance in the parameters examined in this study. We conclude that although alkanes have little effect on whole N. glauca transpiration and biomass gain under normal, nonstressed conditions, they are essential during drought responses, since they enable plants to seal their cuticle upon stomatal closure, thereby reducing leaf death and facilitating a speedy recovery.

Leaf Functional Traits in Relation to Species Composition in an Arctic-Alpine Tundra Grassland

The relict arctic-alpine tundra provides a natural laboratory to study the potential impacts of climate change and anthropogenic disturbance on tundra vegetation. The Nardus stricta-dominated relict tundra grasslands in the Krkonoše Mountains have experienced shifting species dynamics over the past few decades. Changes in species cover of the four competing grasses-Nardus stricta, Calamagrostis villosa, Molinia caerulea, and Deschampsia cespitosa-were successfully detected using orthophotos. Leaf functional traits (anatomy/morphology, element accumulation, leaf pigments, and phenolic compound profiles), were examined in combination with in situ chlorophyll fluorescence in order to shed light on their respective spatial expansions and retreats. Our results suggest a diverse phenolic profile in combination with early leaf expansion and pigment accumulation has aided the expansion of C. villosa, while microhabitats may drive the expansion and decline of D. cespitosa in different areas of the grassland. N. stricta-the dominant species-is retreating, while M. caerulea did not demonstrate significant changes in territory between 2012 and 2018. We propose that the seasonal dynamics of pigment accumulation and canopy formation are important factors when assessing potential "spreader" species and recommend that phenology be taken into account when monitoring grass species using remote sensing.

Transcriptomics Reveals the Effect of Short-Term Freezing on the Signal Transduction and Metabolism of Grapevine

Low temperature is an important factor limiting plant growth. Most cultivars of Vitis vinifera L. are sensitive to low temperatures and are at risk of freezing injury or even plant death during winter. In this study, we analyzed the transcriptome of branches of dormant cv. Cabernet Sauvignon exposed to several low-temperature conditions to identify differentially expressed genes and determine their function based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG)enrichment analyses. Our results indicated that exposure to subzero low temperatures resulted in damage to plant cell membranes and extravasation of intracellular electrolytes, and that this damage increased with decreasing temperature or increasing duration. The number of differential genes increased as the duration of stress increased, but most of the common differentially expressed genes reached their highest expression at 6 h of stress, indicating that 6 h may be a turning point for vines to tolerate extreme low temperatures. Several pathways play key roles in the response of Cabernet Sauvignon to low-temperature injury, namely: (1) the role of calcium/calmodulin-mediated signaling; (2) carbohydrate metabolism, including the hydrolysis of cell wall pectin and cellulose, decomposition of sucrose, synthesis of raffinose, and inhibition of glycolytic processes; (3) the synthesis of unsaturated fatty acids and metabolism of linolenic acid; and (4) the synthesis of secondary metabolites, especially flavonoids. In addition, pathogenesis-related protein may also play a role in plant cold resistance, but the mechanism is not yet clear. This study reveals possible pathways for the freezing response and leads to new insights into the molecular basis of the tolerance to low temperature in grapevine.

Rootstock identity in melon-pumpkin graft combinations determines fruit metabolite profile

Grafting has the potential to improve melon fruit yield and quality, but it is currently held that a lack of compatibility between the rootstock and scion compromises such an effect. To throw light on this subject, we studied melon-pumpkin graft combinations with different levels of compatibility to assess to the effect of the rootstock identity on melon fruit yield and quality, including total fruit ortho-diphenols, total flavonoids, and primary fruit metabolites. Melon cv. 'Kiran' (Ki) was grafted onto three pumpkin rootstocks, 'TZ-148' (TZ), 'Shimshon' (Sh), and '53006' (r53), characterized by high, moderate, and low compatibility, respectively. The non-grafted melon cultivar Ki was used as the control. The incompatible combination Ki/r53 gave the lowest fruit yield and the lowest average fruit weight. In that combination, the content of total ortho-diphenols increased vs. Ki and Ki/TZ and that of total flavonoids decreased vs. Ki/Sh. In addition, concentrations of the amino acids, glutamate, methionine, valine, alanine, glycine, and serine, increased in the pulp of the two compatible combinations, i.e., Ki/TZ and Ki/Sh, suggesting that rootstock identity and compatibility with melon Ki scion modulated amino acid synthesis. Our results show an association between rootstock identity (and level of compatibility with the scion) and an enhancement of fruit nutritional values, i.e., high concentrations of organic acids (determined as citrate, malate, fumarate, and succinate) and soluble carbohydrates (sucrose) were recorded in the pulp of the two compatible combinations, i.e., Ki/TZ and Ki/Sh.

The Influence of Solid and Liquid Systems In Vitro on the Growth and Biosynthetic Characteristics of Microshoot Culture of Spiraea betulifolia ssp. aemiliana

The paper focuses on the growth dynamics and biosynthetic characteristics of the microshoot culture of Spiraea betulifolia ssp. aemiliana obtained in vitro in agar-solidified and liquid media. Microshoots cultured in either type of media showed similar growth dynamics. The most active culture growth was observed from day 35 to day 60. A comparative analysis of the contents of flavonoids and phenol carboxylic acids showed a higher level of phenol carboxylic acids (5.3-6.84%) and a stronger 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity (half-maximal inhibitory concentration: 341 µg/mL) in S. betulifolia ssp. aemiliana microshoots grown in the liquid medium compared to the microshoots cultured in the solid medium. The flavonoid content of the cultured microshoot did not depend on the consistency of the medium. High-performance liquid chromatography (HPLC) was employed to study the profile and levels of phenolic compounds in microshoots, intact plants, and ex vitro-acclimated S. betulifolia ssp. aemiliana plants. The concentration of kaempferol glycosides was found to be higher in microshoots (1.33% in the solid medium, 1.06% in the liquid medium) compared to intact plants and ex vitro-acclimated plants. Thus, the microshoots of S. betulifolia ssp. aemiliana cultured in the liquid medium rapidly increase their biomass and are an inexpensive promising source of biologically active antioxidant substances, mainly phenol carboxylic acids and kaempferol glycosides.

Iron Availability and Homeostasis in Plants: A Review of Responses, Adaptive Mechanisms, and Signaling

Iron is an essential element for all living organisms, playing a major role in plant biochemistry as a redox catalyst based on iron redox properties. Iron is the fourth most abundant element of the Earth's crust, but its uptake by plants is complex because it is often in insoluble forms that are not easily accessible for plants to use. The physical and chemical speciation of iron, as well as rhizosphere activity, are key factors controlling the bioavailability of Fe. Iron can be under reduced (Fe²⁺) or oxidized (Fe³⁺) ionic forms, adsorbed onto mineral surfaces, forming complexes with organic molecules, precipitated to form poorly crystalline hydroxides to highly crystalline iron oxides, or included in crystalline Fe-rich mineral phases. Plants must thus adapt to a complex and changing iron environment, and their response is finely regulated by multiple signaling pathways initiated by a diversity of stimulus perceptions. Higher plants possess two separate strategies to uptake iron from rhizosphere soil: the chelation strategy and the reduction strategy in grass and non-grass plants, respectively. Molecular actors involved in iron uptake and mobilization through the plant have been characterized for both strategies. All these processes that contribute to iron homeostasis in plants are highly regulated in response to iron availability by downstream signaling responses, some of which are characteristic signaling signatures of iron dynamics, while others are shared with other environmental stimuli. Recent research has thus revealed key transcription factors, cis-acting elements, post-translational regulators, and other molecular mechanisms controlling these genes or their encoded proteins in response to iron availability. In addition, the most recent research is increasingly highlighting the crosstalk between iron homeostasis and nutrient response regulation. These regulatory processes help to avoid plant iron concentrations building up to potential cell functioning disruptions that could adversely affect plant fitness. Indeed, when iron is in excess in the plant, it can lead to the production and accumulation of dangerous reactive oxygen species and free radicals (H₂O₂, HO^•, O₂^•-, HO^•₂) that can cause considerable damages to most cellular components. To cope with iron oxidative stress, plants have developed defense systems involving the complementary action of antioxidant enzymes and molecular antioxidants, safe iron-storage mechanisms, and appropriate morphological adaptations.

Multifaceted roles of flavonoids mediating plant-microbe interactions

Plant-microbe interactions dynamically affect plant growth, health, and development. The mechanisms underpinning these associations are-to a large extent-mediated by specialized host-derived secondary metabolites. Flavonoids are one of the most studied classes of such metabolites, regulating both plant development and the interaction with commensal microbes. Here, we provide a comprehensive review of the multiple roles of flavonoids in mediating plant-microbe interactions. First, we briefly summarize the general aspects of flavonoid synthesis, transport, and exudation in plants. Then, we review the importance of flavonoids regulating plant-microbe interactions and dynamically influencing the overall community assembly of plant-root microbiomes. Last, we highlight potential knowledge gaps in our understanding of how flavonoids determine the interactions between plants and commensal microbes. Collectively, we advocate the importance of advancing research in this area toward innovative strategies to effectively manipulate plant-microbiome composition, in this case, via flavonoid production and exudation in plant roots. Video Abstract.

Next-generation sequencing in the biodiversity conservation of endangered medicinal plants

Medicinal plants have been used as traditional herbal medicines in the treatment of various types of diseases. However, the increased demand for these plants highlights the importance of conservation specifically for endangered species. Significant advancements in next-generation sequencing (NGS) technologies have accelerated medicinal plant research while reducing costs and time demands. NGS systems enable high-throughput whole genome sequencing as well as direct RNA sequencing and transcriptome analysis. The sequence data sets created can be used in a variety of areas of study, including biodiversity conservation, comparative genomics, transcriptomic analysis, single cell mining, metagenomics, epigenetics, molecular marker discovery, multi genome sequencing, and so on. Commercial sequencing service providers are constantly working to improve technologies to address bioinformatics problems in NGS data analysis. Several genome sequencing projects on medicinal plants have been completed recently and a few more are in the works. In some medicinal plants, massive NGS-based data has been developed. In the present review, we have attempted to briefly discuss advancements in NGS technology on medicinally essential plants in India. The review will also provide ideas for applying NGS technologies for exploring genomes of various endangered medicinal plants whose genome sequences are not normally available and thus provides valuable insights for the conservation of these vulnerable species.

Therapeutic potential of dietary flavonoid hyperoside against non-communicable diseases: targeting underlying properties of diseases

Non-communicable diseases (NCDs) are a global epidemic with diverse pathogenesis. Among them, oxidative stress and inflammation are the most fundamental co-morbid features. Therefore, multi-targets and multi-pathways therapies with significant anti-oxidant and anti-inflammatory activities are potential effective measures for preventing and treating NCDs. The flavonol glycoside compound hyperoside (Hyp) is widely found in a variety of fruits, vegetables, beverages, and medicinal plants and has various health benefits, especially excellent anti-oxidant and anti-inflammatory properties targeting nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-κB (NF-κB) signaling pathways. In this review, we summarize the pathogenesis associated with oxidative stress and inflammation in NCDs and the biological activity and therapeutic potential of Hyp. Our findings reveal that the anti-oxidant and anti-inflammatory activities regulated by Hyp are associated with numerous biological mechanisms, including positive regulation of mitochondrial function, apoptosis, autophagy, and higher-level biological damage activities. Hyp is thought to be beneficial against organ injuries, cancer, depression, diabetes, and osteoporosis, and is a potent anti-NCDs agent. Additionally, the sources, bioavailability, pharmacy, and safety of Hyp have been established, highlighting the potential to develop Hyp into dietary supplements and nutraceuticals.

Phenylpropanoid metabolism in relation to peel browning development of cold-stored 'Nanguo' pears

Cold-stored 'Nanguo' pears are susceptible to peel browning during subsequent shelf life. In this study, 'Nanguo' pears were cold-stored for different periods to elucidate the metabolism of phenylpropanoid accompanying browning. Changes in phenolics and flavonoids and the crucial enzyme activity and related gene expression involved in the phenylpropanoid pathway were monitored. It was found that the fruit that underwent long-term storage showed peel browning symptoms prior to softening, and the symptom got worse with increasing shelf life. Meanwhile, the accumulation of reactive oxygen species (ROS) and the decrease of ROS scavenging ability were noted. The content of phenolics and flavonoids and the activity and expression of shikimate dehydrogenase (SKDH), phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), and 4-coumarate-CoA ligase (4CL) involved in the phenylpropanoid pathway decreased with prolonged storage. Correlation analysis revealed that browning was positively correlated with ROS accumulation, and the content of phenolics and flavonoids directly affected ROS scavenging ability. In addition, the decrease in phenolics and flavonoids might be owing to the reduced activity of SKDH, PAL, and 4CL and the down-regulated expression of PuPAL and Pu4CL. Collectively, this study indicated that the metabolism of phenylpropanoid is associated with the browning response induced by low-temperature stress.

Mapping and functional characterization of the tomato spotted wilt virus resistance gene SlCHS3 in Solanum lycopersicum

Tomato spotted wilt virus (TSWV) poses a serious threat to tomato (Solanum lycopersicum) production. In this study, tomato inbred line YNAU335 was developed without the Sw-5 locus, which confers resistance or immunity to TSWV (absence of infection). Genetic analysis demonstrated that immunity to TSWV was controlled by a dominant nuclear gene. The candidate genes were mapped into a 20-kb region in the terminal of the long arm of chromosome 9 using bulk segregant analysis and linkage analysis. In this candidate region, a chalcone synthase-encoding gene (SlCHS3) was identified as a strong candidate gene for TSWV resistance. Silencing SlCHS3 reduced flavonoid synthesis, and SlCHS3 overexpression increased flavonoid content. The increase in flavonoids improved TSWV resistance in tomato. These findings indicate that SlCHS3 is indeed involved in the regulation of flavonoid synthesis and plays a significant role in TSWV resistance of YNAU335. This could provide new insights and lay the foundation for analyzing TSWV resistance mechanisms.

Supplementary information

The online version contains supplementary material available at 10.1007/s11032-022-01325-5.

Optimization of Callus and Cell Suspension Cultures of Lycium schweinfurthii for Improved Production of Phenolics, Flavonoids, and Antioxidant Activity

Lycium schweinfurthii is a traditional medicinal plant grown in the Mediterranean region. As it is used in folk medicine to treat stomach ulcers, it took more attention as a source of valuable secondary metabolites. The in vitro cultures of L. schweinfurthii could be a great tool to produce secondary metabolites at low costs. The presented study aimed to introduce and optimize a protocol for inducing callus and cell suspension cultures as well as estimating phenolic, flavonoid compounds, and antioxidant activity in the cultures of the studied species. Three plant growth regulators (PGRs) were supplemented to MS medium solely or in combination to induce callus from leaf explants. The combination between 2,4-dichlorophenoxy acetic acid (2,4-D) and 1-naphthyl acetic acid (NAA) induced callus in all explants regardless of the concentration. The highest fresh weight of callus (3.92 g) was obtained on MS medium fortified with 1 mg L−1 of both 2,4-D and NAA (DN1) after 7 weeks of culture. DN1 was the best medium for callus multiplication regarding the increase in fresh weight and size of callus. Otherwise, the highest phenolics, flavonoids, and antioxidant activity against DPPH free radicals were of callus on MS fortified with 2 mg L−1 NAA (N2). The cell suspension cultures were cultivated on a liquid N2 medium with different sucrose concentrations of 5–30 g L−1 to observe the possible effects on cells’ multiplication and secondary metabolite production. The highest fresh and viable biomass of 12.01 g was obtained on N2 containing 30 g L−1 sucrose. On the other hand, the cell cultures on N2 medium of 5 and 30 g L−1 sucrose produced phenolics and flavonoids, and revealed antioxidant activity against DPPH and ABTS+ free radicals more than other sucrose concentrations. The presented protocol should be useful in the large-scale production of phenolic and flavonoid compounds from callus and cell cultures of L. schweinfurthii.

Growth, Fruit Yield, and Bioactive Compounds of Cherry Tomato in Response to Specific White-Based Full-Spectrum Supplemental LED Lighting

Supplemental artificial light in greenhouses is fundamental to achieving sustainable crop production with high yield and quality. This study’s purpose was to investigate the efficacy of supplemental light (SL) sources on the vegetative and reproductive growth of cherry tomatoes. Four types of light sources were applied, including high-pressure sodium lamps (HPS), a narrow-spectrum LED light (NSL), and two specific full-spectrum LED lights (SFL1 and SFL2) with a shorter blue peak wavelength (436 nm) and/or green peak wavelength (526 nm). The control was the natural light condition. Shoot fresh and dry weight and leaf area in the SFL1 and SFL2 treatments were greater than those in the control. The HPS and NSL treatments also enhanced tomato growth, but they were less efficient compared to the SFL treatments. The SFL1 and SFL2 treatments showed higher fruit yields by 73.1% and 70.7%, respectively, than the control. The SL sources did not affect the effective photochemical quantum yield of photosystem II (Y (II)). However, they did trigger the increased electron transport rate (ETR) and non-photochemical quenching (NPQ). The SFL treatments enhanced tomato growth, fruit yield, and efficient use of light and energy, suggesting that the specific full spectrum based on the short-wavelength blue and/or green peak can be successfully applied for the cultivation of cherry tomato and other crops in greenhouses.

Effect of UV-B Radiation on Flavonoids and Phenols Accumulation in Tempisque (Sideroxylon capiri Pittier) Callus

Tempisque (Sideroxylon capiri Pittier) is classified as a threatened species and has been reported with a high content of phenols and flavonoids in the leaves. The use of abiotic elicitors such as radiation has been reported due to the changes it produces in the metabolism of plants by activating their defense mechanisms and increasing the biosynthesis of bioactive compounds with antioxidant capacity such as phenols and flavonoids. Therefore, the aim of this work was to evaluate the effect of UV-B radiation on growth parameters and the synthesis of bioactive compounds in in vitro culture of tempisque callus. For the callus induction, we used thidiazuron (TDZ) and 2,4-dichlorophenoxyacetic acid (2,4-D) at 0, 0.5 and 1 mg/L. Calluses were exposed to UV-B radiation (0, 1, 2, 3 and 4 h/day) for two and four weeks. The highest callus formation index was obtained with TDZ and 2,4-D at 1 mg/mL. The greatest increase in the concentration of phenols and flavonoids was detected in the fourth week with 4 h of exposure per day. The highest concentrations of quercetin (230 µg/g dry weight), kaempferol (235 µg/g dry weight) and gallic acid (240 µg/g dry weight) were found in callus obtained from leaves explants.

Plant Flavonoids in Mediterranean Species: A Focus on Flavonols as Protective Metabolites under Climate Stress

Flavonoids are specialized metabolites largely widespread in plants where they play numerous roles including defense and signaling under stress conditions. These compounds encompass several chemical subgroups such as flavonols which are one the most represented classes. The most studied flavonols are kaempferol, quercetin and myricetin to which research attributes antioxidative properties and a potential role in UV-defense through UV-screening mechanisms making them critical for plant adaptation to climate change. Despite the great interest in flavonol functions in the last decades, some functional aspects remain under debate. This review summarizes the importance of flavonoids in plant defense against climate stressors and as signal molecules with a focus on flavonols in Mediterranean plant species. The review emphasizes the relationship between flavonol location (at the organ, tissue and cellular scales) and their function as defense metabolites against climate-related stresses. It also provides evidence that biosynthesis of flavonols, or flavonoids as a whole, could be a crucial process allowing plants to adapt to climate change, especially in the Mediterranean area which is considered as one of the most sensitive regions to climate change over the globe.

Screening the Key Region of Sunlight Regulating the Flavonoid Profiles of Young Shoots in Tea Plants (Camellia sinensis L.) Based on a Field Experiment

Both UV and blue light have been reported to regulate the biosynthesis of flavonoids in tea plants; however, the respective contributions of the corresponding regions of sunlight are unclear. Additionally, different tea cultivars may respond differently to altered light conditions. We investigated the responses of different cultivars (‘Longjing 43’, ‘Zhongming 192’, ‘Wanghai 1’, ‘Jingning 1’ and ‘Zhonghuang 2’) to the shade treatments (black and colored nets) regarding the biosynthesis of flavonoids. For all cultivars, flavonol glycosides showed higher sensitivity to light conditions compared with catechins. The levels of total flavonol glycosides in the young shoots of different tea cultivars decreased with the shade percentages of polyethylene nets increasing from 70% to 95%. Myricetin glycosides and quercetin glycosides were more sensitive to light conditions than kaempferol glycosides. The principal component analysis (PCA) result indicated that shade treatment greatly impacted the profiles of flavonoids in different tea samples based on the cultivar characteristics. UV is the crucial region of sunlight enhancing flavonol glycoside biosynthesis in tea shoots, which is also slight impacted by light quality according to the results of the weighted correlation network analysis (WGCNA). This study clarified the contributions of different wavelength regions of sunlight in a field experiment, providing a potential direction for slightly bitter and astringent tea cultivar breeding and instructive guidance for practical field production of premium teas based on light regimes.

Genetic Stability, Phenolic, Flavonoid, Ferulic Acid Contents, and Antioxidant Activity of Micropropagated Lycium schweinfurthii Plants

Lycium schweinfurthii is a Mediterranean wild shrub rich in plant secondary metabolites. In vitro propagation of this plant may support the production of valuable dietary supplements for humanity, introduction of it to the world market, and opportunities for further studies. The presented study aimed to introduce an efficient and reproducible protocol for in vitro micropropagation of L. schweinfurthii and assess the genetic stability of micropropagated plants (MiPs) as well as to estimate phenolic, flavonoid, ferulic acid contents, and the antioxidant activity in leaves of micropropagated plants. Two DNA-based techniques, random amplified polymorphic DNA (RAPD) and inter-simple sequence repeats (ISSR), and one biochemical technique, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), were used to assess the genetic stability in MiPs. Spectrophotometric analysis was performed to estimate total phenolic and flavonoid contents and antioxidant activity of MiPs leaves, while ferulic acid content was estimated using high-performance thin-layer chromatography (HPTLC). Sufficient shoot proliferation was achieved at MS (Murashige and Skoog) medium supplemented with 0.4 mg L^-1 kinetin and rooted successfully on half-strength MS medium fortified with 0.4 mg L^-1 Indole-3-butyric acid (IBA). The Jaccard's similarity coefficients detected in MiPs reached 52%, 55%, and 82% in the RAPD, ISSR, and SDS-PAGE analyses, respectively. In the dried leaves of MiPs, the phenolic, flavonoid, and ferulic acid contents of 11.53 mg gallic acid equivalent, 12.99 mg catechin equivalent, and 45.52 mg were estimated per gram, respectively. However, an IC₅₀ of 0.43, and 1.99 mg mL^-1 of MiP dried leaves' methanolic extract was required to scavenge half of the DPPH, and ABTS free radicals, respectively. The study presented a successful protocol for in vitro propagation of a valued promising plant source of phenolic compounds.

The role of quercetin in plants

Flavonoids are a special category of hydroxylated phenolic compounds having an aromatic ring structure. Quercetin is aspecial subclass of flavonoid. It is a bioactive natural compound built upon the flavon structure nC6(ring A)-C3(ring C)-C6(ring B). Quercetin facilitates several plant physiological processes, such as seed germination, pollen growth, antioxidant machinery, and photosynthesis, as well as induces proper plant growth and development. Quercetin is a powerful antioxidant, so it potently provides plant tolerance against several biotic and abiotic stresses. This review highlights quercetin's role in increasing several physiological and biochemical processes under stress and non-stress environments. Additionally, this review briefly assesses quercetin's role in mitigating biotic and abiotic stresses (e.g., salt, heavy metal, and UV stress). The biosynthesis of flavonoids, their signaling pathways, and quercetin's role in plant signaling are also discussed.

Plant growth and metabolic changes in 'Super Hot' chili fruit (Capsicum annuum) exposed to supplemental LED lights

Light-emitting diodes (LEDs) of different colors improve plant growth and increase levels of secondary metabolites. This study aimed to determine the effect of red, blue, and red + blue LEDs (1:1) on the secondary metabolites composition in chili, focusing on capsaicinoids, at the top and middle of the plant canopy in 'Super Hot' chili. The accumulated yield of the chili fruit was the highest for control, followed by blue, red and red + blue LEDs, with the top canopy giving twice more yield than the middle canopy. UPLC-MS/MS analysis of chili fruit's methanolic extracts was used to determine capsaicinoids levels. Blue LEDs significantly increased nordihydrocapsaicin, capsaicin, dihydrocapsaicin, homocapsaicin and homodihydrocapsaicin contents by 57 %, 43 %, 56 %, 28 %, and 54 %, respectively, compared to the control. Also, 24 tentatively annotated metabolites, including phenylalanine, cinnamate, and valine, which are involved in the biosynthesis of capsaicinoids, were semi-quantitatively evaluated to determine the impact of LED exposure on the biosynthetic pathway of capsaicinoids. Supplemental blue LED placed at the top and between the canopy may boost the levels of capsaicinoids in chili fruit grown in greenhouses.

Structure and contingency determine mutational hotspots for flower color evolution

Evolutionary genetic studies have uncovered abundant evidence for genomic hotspots of phenotypic evolution, as well as biased patterns of mutations at those loci. However, the theoretical basis for this concentration of particular types of mutations at particular loci remains largely unexplored. In addition, historical contingency is known to play a major role in evolutionary trajectories, but has not been reconciled with the existence of such hotspots. For example, do the appearance of hotspots and the fixation of different types of mutations at those loci depend on the starting state and/or on the nature and direction of selection? Here, we use a computational approach to examine these questions, focusing the anthocyanin pigmentation pathway, which has been extensively studied in the context of flower color transitions. We investigate two transitions that are common in nature, the transition from blue to purple pigmentation and from purple to red pigmentation. Both sets of simulated transitions occur with a small number of mutations at just four loci and show strikingly similar peaked shapes of evolutionary trajectories, with the mutations of the largest effect occurring early but not first. Nevertheless, the types of mutations (biochemical vs. regulatory) as well as their direction and magnitude are contingent on the particular transition. These simulated color transitions largely mirror findings from natural flower color transitions, which are known to occur via repeated changes at a few hotspot loci. Still, some types of mutations observed in our simulated color evolution are rarely observed in nature, suggesting that pleiotropic effects further limit the trajectories between color phenotypes. Overall, our results indicate that the branching structure of the pathway leads to a predictable concentration of evolutionary change at the hotspot loci, but the types of mutations at these loci and their order is contingent on the evolutionary context.

The Role of Polyphenols in Abiotic Stress Response: The Influence of Molecular Structure

Abiotic stressors such as extreme temperatures, drought, flood, light, salt, and heavy metals alter biological diversity and crop production worldwide. Therefore, it is important to know the mechanisms by which plants cope with stress conditions. Polyphenols, which are the largest group of plant-specialized metabolites, are generally recognized as molecules involved in stress protection in plants. This diverse group of metabolites contains various structures, from simple forms consisting of one aromatic ring to more complex ones consisting of large number of polymerized molecules. Consequently, all these molecules, depending on their structure, may show different roles in plant growth, development, and stress protection. In the present review, we aimed to summarize data on how different polyphenol structures influence their biological activity and their roles in abiotic stress responses. We focused our review on phenolic acids, flavonoids, stilbenoids, and lignans.

Increase in longevity and amelioration of pesticide toxicity by natural levels of dietary phytochemicals in the honey bee, Apis mellifera

For the past decade, migratory beekeepers who provide honey bees for pollination services have experienced substantial colony losses on a recurring basis that have been attributed in part to exposure to insecticides, fungicides, or their combinations applied to crops. The phytochemicals p-coumaric acid and quercetin, which occur naturally in a wide variety of bee foods, including beebread and many types of honey, can enhance adult bee longevity and reduce the toxicity of certain pesticides. How variation in concentrations of natural dietary constituents affects interactions with xenobiotics, including synthetic pesticides, encountered in agroecosystems remains an open question. We tested the effects of these two phytochemicals at a range of natural concentrations on impacts of consuming propiconazole and chlorantraniliprole, a triazole fungicide and an insecticide frequently applied as a tank mix to almond trees during bloom in California's Central Valley. Propiconazole, even at low field concentrations, significantly reduced survival and longevity when consumed by adult bees in a sugar-based diet. The effects of propiconazole in combination with chlorantraniliprole enhanced mortality risk. The detrimental effects of the two pesticides were for the most part reduced when either or both of the phytochemicals were present in the diet. These findings suggest that honey bees may depend on non-nutritive but physiologically active phytochemical components of their natural foods for ameliorating xenobiotic stress, although only over a certain range of concentrations; particularly at the high end of the natural range, certain combinations can incur additive toxicity. Thus, efforts to develop nectar or pollen substitutes with phytochemicals to boost insecticide tolerance or immunity or to evaluate toxicity of pesticides to pollinators should take concentration-dependent effects of phytochemicals into consideration.

Functional characterization of three flavonol synthase genes from Camellia sinensis: Roles in flavonol accumulation

Flavonol derivatives are a group of flavonoids benefiting human health. Their abundant presence in tea is associated with astringent taste. To date, mechanism pertaining to the biosynthesis of flavonols in tea plants remains unknown. In this study, we used bioinformatic analysis mining the tea genome and obtained three cDNAs that were annotated to encode flavonol synthases (FLS). Three cDNAs, namely CsFLSa, b, and c, were heterogenously expressed in E. coli to induce recombinant proteins, which were further used to incubate with three substrates, dihydrokampferol (DHK), dihydroquercetin (DHQ), and dihydromyricetin (DHM). The resulting data showed that three rCsFLSs preferred to catalyze (DHK). Overexpression of each cDNA in tobacco led to the increase of kampferol and the reduction of anthocyanins in flowers. Further metabolic profiling of flavan-3-ols in young tea shoots characterized that kaempferol derivatives were the most abundant, followed by quercetin and then myricetin derivatives. Taken together, these data characterized the key step committed to the biosynthesis of flavonols in tea leaves. Moreover, these data enhance understanding the metabolic accumulation relevance between flavonols and other main flavonoids such as flavan-3-ols in tea leaves.

Phenotypic, Phytochemical, and Transcriptomic Analysis of Black Sorghum (Sorghum bicolor L.) Pericarp in Response to Light Quality

Black sorghum [Sorghum bicolor (L.) Moench] is characterized by the black appearance of the pericarp and production of 3-deoxyanthocyanidins (3-DOA), which are valued for their cytotoxicity to cancer cells and as natural food colorants and antioxidant additives. The black pericarp phenotype is not fully penetrant in all environments, which implicates the light spectrum and/or photoperiod as the critical factor for trait expression. In this study, black- or red-pericarp genotypes were grown under regimes of visible light, visible light supplemented with UVA or supplemented with UVA plus UVB (or dark control). Pericarp 3-DOAs and pericarp pigmentation were maximized in the black genotype exposed to a light regime supplemented with UVB. Changes in gene expression during black pericarp development revealed that ultraviolet light activates genes related to plant defense, reactive oxygen species, and secondary metabolism, suggesting that 3-DOA accumulation is associated with activation of flavonoid biosynthesis and several overlapping defense and stress signaling pathways.

Overexpression of OsF3H modulates WBPH stress by alteration of phenylpropanoid pathway at a transcriptomic and metabolomic level in Oryza sativa

The whitebacked planthopper (WBPH), has become a devastating pest for rice crops, causes serious yield losses each year, and urgently needs biological control. Here, we developed a WBPH-resistant rice cultivar by overexpressing the OsF3H gene. A genetic functional analysis of the OsF3H gene confirmed its role in facilitating flavonoid contents and have indicated that the expression of the OsF3H gene is involved in regulation of the downstream genes (OsDFR and OsFLS) of the flavonoid pathway and genes (OsSLR1 and OsWRKY13) involved in other physiological pathways. OxF3H (OsF3H transgenic) plants accumulated significant amounts of the flavonols kaempferol (Kr) and quercetin (Qu) and the anthocyanins delphinidin and cyanidin, compared to the wild type, in response to the stress induced by WBPH. Similarly, OsF3H-related proteins were significantly expressed in OxF3H lines after WBPH infestation. The present study, indicated that the regulation of JA in OxF3H plants was suppressed due the overexpression of the OsF3H gene, which induced the expression of downstream genes related to anthocyanin. Similarly, the OsWRKY13 transcriptional factor was significantly suppressed in OxF3H plants during WBPH infestation. Exogenous application of Kr and Qu increased the survival rates of susceptible TN1 lines in response to WBPH, while decreased the survival rate of first instar WBPHs, indicating that both flavonols exhibit pesticide activity. Phenotypic demonstration also affirms that OxF3H plants show strong resistance to WBPH compared with wild type. Collectively, our result suggested that OsF3H overexpression led to the up-regulation of defense related genes and enhanced rice resistance to WBPH infestation.

Transcriptional differentiation of UV-B protectant genes in maize landraces spanning an elevational gradient in Chiapas, Mexico

Globally, farmers cultivate and maintain crop landraces (i.e., traditional varieties). Landraces contain unique diversity shaped in part by natural and human-mediated selection and are an indispensable resource for farmers. Since environmental conditions change with elevation, crop landraces grown along elevational gradients have provided ideal locations to explore patterns of local adaptation. To further probe traits underlying this differentiation, transcriptome signatures can help provide a foundation for understanding the ways in which functional genetic diversity may be shaped by environment. In this study, we returned to an elevational gradient in Chiapas, Mexico, to assess transcriptional differentiation of genes underlying UV-B protection in locally adapted maize landraces from multiple elevations. We collected and planted landraces from three elevational zones (lowland, approximately 600 m; midland, approximately 1,550 m; highland approximately 2,100 m) in a common garden at 1,531 m. Using RNA-seq data derived from leaf tissue, we performed differential expression analysis between maize from these distinct elevations. Highland and lowland landraces displayed differential expression in phenylpropanoid and flavonoid biosynthesis genes involved in the production of UV-B protectants and did so at a rate greater than expected based on observed background transcriptional differentiation across the genome. These findings provide evidence for the differentiation of suites of genes involved in complex ecologically relevant pathways. Thus, while neutral evolutionary processes may have played a role in the observed patterns of differentiation, UV-B may have also acted as a selective pressure to differentiate maize landraces in the region. Studies of the distribution of functional crop genetic diversity across variable landscapes can aid us in understanding the response of diversity to abiotic/biotic change and, ultimately, may facilitate its conservation and utilization.

Flavonoids are indispensable for complete male fertility in rice

Flavonoids are essential for male fertility in some but not all plant species. In rice (Oryza sativa), the chalcone synthase mutant oschs1 produces flavonoid-depleted pollen and is male sterile. The mutant pollen grains are viable with normal structure, but they display reduced germination rate and pollen-tube length. Analysis of oschs1/+ heterozygous lines shows that pollen flavonoid deposition is a paternal effect and fertility is independent of the haploid genotypes (OsCHS1 or oschs1). To understand which classes of flavonoids are involved in male fertility, we conducted detailed analysis of rice mutants for branch-point enzymes of the downstream flavonoid pathways, including flavanone 3-hydroxylase (OsF3H; flavonol pathway entry enzyme), flavone synthase II (CYP93G1; flavone pathway entry enzyme), and flavanone 2-hydroxylase (CYP93G2; flavone C-glycoside pathway entry enzyme). Rice osf3h and cyp93g1 cyp93g2 CRISPR/Cas9 mutants, and cyp93g1 and cyp93g2 T-DNA insertion mutants showed altered flavonoid profiles in anthers, but only the osf3h and cyp93g1 cyp93g2 mutants displayed reduction in seed yield. Our findings indicate that flavonoids are essential for complete male fertility in rice and a combination of different classes (flavanones, flavonols, flavones, and flavone C-glycosides) appears to be important, as opposed to the essential role played primarily by flavonols that has been previously reported in several plant species.

Flavonoids and Mitochondria: Activation of Cytoprotective Pathways?

A large number of diverse mechanisms that lead to cytoprotection have been described to date. Perhaps, not surprisingly, the role of mitochondria in these phenomena is notable. In addition to being metabolic centers, due to their role in cell catabolism, ATP synthesis, and biosynthesis these organelles are triggers and/or end-effectors of a large number of signaling pathways. Their role in the regulation of the intrinsic apoptotic pathway, calcium homeostasis, and reactive oxygen species signaling is well documented. In this review, we aim to characterize the prospects of influencing cytoprotective mitochondrial signaling routes by natural substances of plant origin, namely, flavonoids (e.g., flavanones, flavones, flavonols, flavan-3-ols, anthocyanidins, and isoflavones). Flavonoids are a family of widely distributed plant secondary metabolites known for their beneficial effects on human health and are widely applied in traditional medicine. Their pharmacological characteristics include antioxidative, anticarcinogenic, anti-inflammatory, antibacterial, and antidiabetic properties. Here, we focus on presenting mitochondria-mediated cytoprotection against various insults. Thus, the role of flavonoids as antioxidants and modulators of antioxidant cellular response, apoptosis, mitochondrial biogenesis, autophagy, and fission and fusion is reported. Finally, an emerging field of flavonoid-mediated changes in the activity of mitochondrial ion channels and their role in cytoprotection is outlined.

CsMYB60 directly and indirectly activates structural genes to promote the biosynthesis of flavonols and proanthocyanidins in cucumber

Flavonols and proanthocyanidins (PAs) are the main pigments in the black spines of cucumber (Cucumis sativus) fruit, and CsMYB60 is a key regulator of the biosynthesis of flavonols and PAs. However, in cucumber, the tissue distribution pattern of flavonols and PAs and the mechanism of their biosynthesis regulated by CsMYB60 remain unclear. In this study, we clarified the tissue-specific distribution of flavonoids and the unique transcriptional regulation of flavonoid biosynthesis in cucumber. CsMYB60 activated CsFLS and CsLAR by binding to their promoters and directly or indirectly promoted the expression of CsbHLH42, CsMYC1, CsWD40, and CsTATA-box binding protein, resulting in the formation of complexes of these four proteins to increase the expression of Cs4CL and interact with CsTATA-box binding protein to regulate the expression of CsCHS, thereby regulating the biosynthesis of flavonols and PAs in cucumber. Our data provide new insights into the molecular mechanism of flavonoid biosynthesis, which will facilitate molecular breeding to improve fruit quality in cucumber.

The style and substance of plant flavonoid decoration; towards defining both structure and function

Over 8000 different flavonoids have been described and a considerable number of new flavonoid structures are being elucidated every year. The advent of metabolomics alongside the development of phytochemical genetics - wherein the genetic basis underlying the regulation of the levels of plant metabolites is determined - has provided a massive boost to such efforts. That said our understanding of the individual function(s) of the vast majority of the metabolites that constitute this important class of phytochemicals remains unknown. Here we review what is known concerning the major decorative modifications of flavonoids in plants, namely hydroxylation, glycosylation, methylation and acylation. Our major focus is with regard to the in planta function of these modified compounds, however, we also highlight the demonstrated bioactive roles which they possess. We additionally performed a comprehensive survey of the flavonoids listed in the KNApSAcK database in order to assess the frequency of occurrence of each type of flavonoid modification. We conclude that whilst considerable research has been carried out regarding the biological roles of flavonoids most studies to date have merely provided information on the compound class or sub-classes thereof as a whole with too little currently known on the specific role of individual metabolites. We, therefore, finally suggest a framework based on currently available tools by which the relative importance of the individual compounds can be assessed under various biological conditions in order to fill this knowledge-gap.

UV-B Radiation Largely Promoted the Transformation of Primary Metabolites to Phenols in Astragalus mongholicus Seedlings

: Ultraviolet-B (UV-B) radiation (280-320 nm) may induce photobiological stress in plants, activate the plant defense system, and induce changes of metabolites. In our previous work, we found that between the two Astragalus varieties prescribed by the Chinese Pharmacopoeia, Astragalus mongholicus has better tolerance to UV-B. Thus, it is necessary to study the metabolic strategy of Astragalus under UV-B radiation further. In the present study, we used untargeted gas chromatography-mass spectrometry (GC-MS) and targeted liquid chromatography-mass spectrometry (LC-MS techniques) to investigate the profiles of primary and secondary metabolic. The profiles revealed the metabolic response of Astragalus to UV-B radiation. We then used real-time polymerase chain reaction (RT-PCR) to obtain the transcription level of relevant genes under UV-B radiation (UV-B supplemented in the field, λmax = 313 nm, 30 W, lamp-leaf distance = 60 cm, 40 min·day-1), which annotated the responsive mechanism of phenolic metabolism in roots. Our results indicated that supplemental UV-B radiation induced a stronger shift from carbon assimilation to carbon accumulation. The flux through the phenylpropanoids pathway increased due to the mobilization of carbon reserves. The response of metabolism was observed to be significantly tissue-specific upon the UV-B radiation treatment. Among phenolic compounds, C6C1 carbon compounds (phenolic acids in leaves) and C6C3C6 carbon compounds (flavones in leaves and isoflavones in roots) increased at the expense of C6C3 carbon compounds. Verification experiments show that the response of phenolics in roots to UV-B is activated by upregulation of relevant genes rather than phenylalanine. Overall, this study reveals the tissues-specific alteration and mechanism of primary and secondary metabolic strategy in response to UV-B radiation.

Convergent Evolution at the Pathway Level: Predictable Regulatory Changes during Flower Color Transitions

The predictability of evolution, or whether lineages repeatedly follow the same evolutionary trajectories during phenotypic convergence remains an open question of evolutionary biology. In this study, we investigate evolutionary convergence at the biochemical pathway level and test the predictability of evolution using floral anthocyanin pigmentation, a trait with a well-understood genetic and regulatory basis. We reconstructed the evolution of floral anthocyanin content across 28 species of the Andean clade Iochrominae (Solanaceae) and investigated how shifts in pigmentation are related to changes in expression of seven key anthocyanin pathway genes. We used phylogenetic multivariate analysis of gene expression to test for phenotypic and developmental convergence at a macroevolutionary scale. Our results show that the four independent losses of the ancestral pigment delphinidin involved convergent losses of expression of the three late pathway genes (F3'5'h, Dfr, and Ans). Transitions between pigment types affecting floral hue (e.g., blue to red) involve changes to the expression of branching genes F3'h and F3'5'h, while the expression levels of early steps of the pathway are strongly conserved in all species. These patterns support the idea that the macroevolution of floral pigmentation follows predictable evolutionary trajectories to reach convergent phenotype space, repeatedly involving regulatory changes. This is likely driven by constraints at the pathway level, such as pleiotropy and regulatory structure.

Genetic Variation Related to High Elevation Adaptation Revealed by Common Garden Experiments in Pinus yunnanensis

Local adaptation, adaptation to specialized niches and environmental clines have been extensively reported for forest trees. Investigation of the adaptive genetic variation is crucial for forest resource management and breeding, especially in the context of global climate change. Here, we utilized a Pinus yunnanensis common garden experiments established at high and low elevation sites to assess the differences in growth and survival among populations and between the two common garden sites. The studied traits showed significant variation between the two test sites and among populations, suggesting adaptive divergence. To detect genetic variation related to environment, we captured 103,608 high quality SNPs based on RNA sequencing, and used them to assess the genetic diversity and population structure. We identified 321 outlier SNPs from 131 genes showing significant divergence in allelic frequency between survival populations of two sites. Functional categories associated with adaptation to high elevation were found to be related to flavonoid biosynthesis, response to UV, DNA repair, response to reactive oxygen species, and membrane lipid metabolic process. Further investigation of the outlier genes showed overrepresentation of the flavonoid biosynthesis pathway, suggesting that this pathway may play a key role in P. yunnanensis adaptation to high elevation environments. The outlier genes identified, and their variants, provide a basic reference for advanced investigations.

Computational Modeling of Anthocyanin Pathway Evolution: Biases, Hotspots, and Trade-offs

The alteration of metabolic pathways is a common mechanism underlying the evolution of new phenotypes. Flower color is a striking example of the importance of metabolic evolution in a complex phenotype, wherein shifts in the activity of the underlying pathway lead to a wide range of pigments. Although experimental work has identified common classes of mutations responsible for transitions among colors, we lack a unifying model that relates pathway function and activity to the evolution of distinct pigment phenotypes. One challenge in creating such a model is the branching structure of pigment pathways, which may lead to evolutionary trade-offs due to competition for shared substrates. In order to predict the effects of shifts in enzyme function and activity on pigment production, we created a simple kinetic model of a major plant pigmentation pathway: the anthocyanin pathway. This model describes the production of the three classes of blue, purple, and red anthocyanin pigments, and accordingly, includes multiple branches and substrate competition. We first studied the general behavior of this model using a naïve set of parameters. We then stochastically evolved the pathway toward a defined optimum and analyzed the patterns of fixed mutations. This approach allowed us to quantify the probability density of trajectories through pathway state space and identify the types and number of changes. Finally, we examined whether our simulated results qualitatively align with experimental observations, i.e., the predominance of mutations which change color by altering the function of branching genes in the pathway. These analyses provide a theoretical framework that can be used to predict the consequences of new mutations in terms of both pigment phenotypes and pleiotropic effects.

Can natural products improve skin photoprotection?

Abstract Due to increased UV radiation on the Earth’s surface, caused by depletion of the stratospheric ozone, people have become more susceptible to different types of skin damage, such as erythema, sunburns, and cancer; this is especially of concern in tropical countries. Thus, efforts to improve awareness as well as the use of sunscreen are increasing worldwide. However, synthetic UV filters have been associated with deleterious effects such as photosensitization. Natural products have been used by ancient cultures for several purposes, including protecting the skin from the sun. However, there is still doubt today whether photoprotection is a real phenomenom or whether it is simply tanning of the skin. Plants have self-protective mechanisms and produce secondary metabolites that can protect themselves from UV radiation. Yet, can phytochemical compounds protect human skin? This review discusses the paradoxical effect of chemical UV filters and the influence of phytochemicals in in vitro and in vivo tests of photoprotection.