Responses of the flavonoid pathway to UV-B radiation stress and the correlation with the lipid antioxidant characteristics in the desert plant Caryopteris mongolica

Haplotype-resolved genome assembly of Phanera championii reveals molecular mechanisms of flavonoid synthesis and adaptive evolution

Phanera championii is a medicinal liana plant that has successfully adapted to hostile karst habitats. Despite extensive research on its medicinal components and pharmacological effects, the molecular mechanisms underlying the biosynthesis of critical flavonoids and its adaptation to karst habitats remain elusive. In this study, we performed high-coverage PacBio and Hi-C sequencing of P. championii, which revealed its high heterozygosity and phased the genome into two haplotypes: Hap1 (384.60 Mb) and Hap2 (383.70 Mb), encompassing a total of 58 612 annotated genes. Comparative genomes analysis revealed that P. championii experienced two whole-genome duplications (WGDs), with approximately 59.59% of genes originating from WGD events, thereby providing a valuable genetic resource for P. championii. Moreover, we identified a total of 112 genes that were strongly positively selected. Additionally, about 81.60 Mb of structural variations between the two haplotypes. The allele-specific expression patterns suggested that the dominant effect of P. championii was the elimination of deleterious mutations and the promotion of beneficial mutations to enhance fitness. Moreover, our transcriptome and metabolome analysis revealed alleles in different tissues or different haplotypes collectively regulate the synthesis of flavonoid metabolites. In summary, our comprehensive study highlights the significance of genomic and morphological adaptation in the successful adaptation of P. championii to karst habitats. The high-quality phased genomes obtained in this study serve as invaluable genomic resources for various applications, including germplasm conservation, breeding, evolutionary studies, and elucidation of pathways governing key biological traits of P. championii.

Flavonoid synthesis in Lamiophlomis rotata from Qinghai-Tibet Plateau is influenced by soil properties, microbial community, and gene expression

Lamiophlomis rotata is a medicinal plant in Qinghai-Tibet Plateau, in which flavonoid compounds are the major medicinal components. However, it remains unclear how flavonoid metabolism of L. rotata is influenced by soil properties and microbial community. In this study, we collected L. rotata seedlings and rhizosphere soils from five habitats ranging from 3750 to 4270 m of altitude and analyzed the effects of habitat conditions on flavonoid metabolism. The activities of peroxidase, cellulase, and urease were increased with altitude, while those of alkaline phosphatase, alkaline protease, and sucrase were decreased with altitude. Analysis of OTUs showed that the total number of bacterial genera was higher than that of fungal genera. The highest number of fungal genera was 132, and that of bacterial genera was 33 in Batang (BT) town in Yushu County at an altitude of 3880 m, suggesting that the fungal communities may play a critical role in L. rotata rhizosphere soils. Flavonoids in leaves and roots of L. rotata shared a similar pattern, with a trend of increasing levels with altitude. The highest flavonoid content measured, 12.94 mg/g in leaves and 11.43 mg/g in roots, was from Zaduo (ZD) County at an altitude of 4208 m. Soil peroxidases affected quercetin content in leaves of L. rotata, while the fungus Sebacina affected flavonoid content in leaves and roots of L. rotata. The expression of PAL, F3'H, FLS, and FNS genes showed a declining trend in leaves with altitude, while F3H showed an increasing trend in both leaves and roots. Overall, soil physicochemical properties and microbial community affect flavonoid metabolism in L. rotata in Qinghai-Tibet Plateau. The variations in flavonoid content and gene expression as well as their associations with soil factors revealed the complexity of the growth conditions and genetic makeup in L. rotata habitats of Qinghai-Tibet Plateau.

UV-B promotes flavonoid biosynthesis in Ginkgo biloba by inducing the GbHY5-GbMYB1-GbFLS module

Ginkgo biloba (ginkgo) leaves have medicinal value due to their high levels of secondary metabolites, such as flavonoids. We found that the flavonoid content in ginkgo leaves increases significantly at high altitudes (Qinghai-Tibet Plateau). Considering that high UV-B radiation is among the key environmental characteristics of the Qinghai-Tibet Plateau, we carried out simulated UV-B treatments on ginkgo seedlings and found that the flavonoid content of the leaves increased significantly following the treatments. Combined with results from our previous studies, we determined that the transcription factor GbHY5 may play a key role in responses to UV-B radiation. Overexpression of GbHY5 significantly promoted the accumulation of flavonoids in both ginkgo callus and Arabidopsis thaliana. Furthermore, yeast two-hybrid and real-time quantitative PCR showed that GbHY5 promoted the expression of GbMYB1 by interacting with GbMYB1 protein. Overexpression of GbMYB1 in ginkgo callus and A. thaliana also significantly promoted flavonoid biosynthesis. GbFLS encodes a key enzyme in flavonoid biosynthesis, and its promoter has binding elements of GbHY5 and GbMYB1. A dual-luciferase reporter assay indicated that while GbHY5 and GbMYB1 activated the expression of GbFLS individually, their co-expression achieved greater activation. Our analyses reveal the molecular mechanisms by which the UV-B-induced GbHY5-GbMYB1-GbFLS module promotes flavonoid biosynthesis in ginkgo, and they provide insight into the use of UV-B radiation to enhance the flavonoid content of ginkgo leaves.

Protective and defensive role of anthocyanins under plant abiotic and biotic stresses: An emerging application in sustainable agriculture

Global warming is the major cause of abiotic and biotic stresses that reduce plant growth and productivity. Various stresses such as drought, low temperature, pathogen attack, high temperature and salinity all negatively influence plant growth and development. Due to sessile beings, they cannot escape from these adverse conditions. However, plants develop a variety of systems that can help them to tolerate, resist, and escape challenges imposed by the environment. Among them, anthocyanins are a good example of stress mitigators. They aid plant growth and development by increasing anthocyanin accumulation, which leads to increased resistance to various biotic and abiotic stresses. In the primary metabolism of plants, anthocyanin improves the photosynthesis rate, membrane permeability, up-regulates many enzyme transcripts related to anthocyanin biosynthesis, and optimizes nutrient uptake. Generally, the most important genes of the anthocyanin biosynthesis pathways were up-regulated under various abiotic and biotic stresses. The present review will highlight anthocyanin mediated stress tolerance in plants under various abiotic and biotic stresses. We have also compiled literature related to genetically engineer stress-tolerant crops generated using over-expression of genes belonging to anthocyanin biosynthetic pathway or its regulation. To sum up, the present review provides an up-to-date description of various signal transduction mechanisms that modulate or enhance anthocyanin accumulation under stress conditions.

Effects of plant growth regulators on the contents of rutin, hyperoside and quercetin in Hypericum attenuatum Choisy

To explore the accumulation of rutin, hyperoside and quercetin in Hypericum attenuatum Choisy under treatment with different plant growth regulators, 100 mg/L, 200 mg/L and 300 mg/L cycocel, 100 mg/L, 200 mg/L and 300 mg/L mepiquat chloride and 1 mg/L, 2 mg/L and 3 mg/L naphthalene acetic acid were foliage sprayed on Hypericum attenuatum Choisy plants at the early growth stage. We sampled and determined the important flavonoid contents at the flowering stage. The results showed that the three plant growth regulators had different effects on the accumulation of rutin, hyperoside and quercetin in the leaves, stems and flowers of Hypericum attenuatum Choisy at the flowering stage. After spraying 1 mg/L naphthalene acetic acid at the early growth stage, the rutin contents in the leaves, stems and flowers increased by approximately 60.33%, 223.85% and 192.02%, respectively (P < 0.05). Spraying 100 mg/L mepiquat chloride increased the hyperoside contents in the leaves and flowers by approximately 7.77% and 12.87%, respectively (P < 0.05). Spraying 2 mg/L naphthalene acetic acid significantly increased the quercetin contents in the flowers and leaves by approximately 95.62% and 47.85%, respectively (P < 0.05). Therefore, at the early growth stage, spraying 1 mg/L naphthalene acetic acid significantly increased rutin content, spraying 100 mg/L mepiquat chloride significantly increased hyperoside content, and spraying 2 mg/L naphthalene acetic acid significantly increased quercetin content in Hypericum attenuatum Choisy. In conclusion, the accumulation of flavonoids in Hypericum attenuatum Choisy was regulated by plant growth regulators.

Foliar and Root Comparative Metabolomics and Phenolic Profiling of Micro-Tom Tomato (Solanum lycopersicum L.) Plants Associated with a Gene Expression Analysis in Response to Short Daily UV Treatments

Tomato (Solanum lycopersicum L.) is globally recognised as a high-value crop both for commercial profit and nutritional benefits. In contrast to the extensive data regarding the changes in the metabolism of tomato fruit exposed to UV radiation, less is known about the foliar and root metabolome. Using an untargeted metabolomic approach through UHPLC-ESI-QTOF-MS analysis, we detected thousands of metabolites in the leaves (3000) and roots (2800) of Micro-Tom tomato plants exposed to 11 days of short daily UV radiation, applied only on the aboveground organs. Multivariate statistical analysis, such as OPLS-DA and volcano, were performed to allow a better understanding of the modifications caused by the treatment. Based on the unexpected modulation to the secondary metabolism, especially the phenylpropanoid pathway, of which compounds were down and up accumulated respectively in leaves and roots of treated plants, a phenolic profiling was carried out for both organs. The phenolic profile was associated with a gene expression analysis to check the transcription trend of genes involved in the UVR8 signalling pathway and the early steps of the phenolic biosynthesis. The retention of the modifications at metabolic and phenolic levels was also investigated 3 days after the UV treatment, showing a prolonged effect on the modulation once the UV treatment had ceased.

Phosphoproteomics Reveals Regulation of Secondary Metabolites in Mahonia bealei Exposed to Ultraviolet-B Radiation

Mahonia bealei (M. bealei) is a traditional Chinese medicine containing a high alkaloid content used to treat various diseases. Generally, only dried root and stem are used as medicines, considering that the alkaloid content in M. bealei leaves is lower than in the stems and roots. Some previous research found that alkaloid and flavonoid contents in the M. bealei leaves may increase when exposed to ultraviolet B (UV-B) radiation. However, the underlying mechanism of action is still unclear. In this study, we used titanium dioxide material enrichment and mass-based label-free quantitative proteomics techniques to explore the effect and mechanism of M. bealei leaves when exposed to UV-B treatment. Our data suggest that UV-B radiation increases the ATP content, photosynthetic pigment content, and some enzymatic/nonenzymatic indicators in the leaves of M. bealei. Moreover, phosphoproteomics suggests phosphoproteins related to mitogen-activated protein kinase (MAPK) signal transduction and the plant hormone brassinosteroid signaling pathway as well as phosphoproteins related to photosynthesis, glycolysis, the tricarboxylic acid cycle, and the amino acid synthesis/metabolism pathway are all affected by UV-B radiation. These results suggest that the UV-B radiation activates the oxidative stress response, MAPK signal transduction pathway, and photosynthetic energy metabolism pathway, which may lead to the accumulation of secondary metabolites in M. bealei leaves.

The effect of flue-curing procedure on the dynamic change of microbial diversity of tobaccos

The purpose of the study is to explore the effect of flue-curing procedure on the diversity of microbial communities in tobaccos and the dynamic change of compositions of microbial communities in the flue-curing process. It expects to provide a theoretical basis for the application of microbes in tobacco leaves and a theoretical basis and idea for optimization of the flue-curing technologies. By investigating tobacco variety K326, the tests were carried out for comparing the conventional flue-curing procedure and dry-ball temperature set and wet-ball temperature degradation flue-curing procedure. Based on the culture-independent approach and high-throughput sequencing procedure, the relationship between the flue-curing procedure for tobaccos and microbial communities in tobaccos was revealed by measuring the dynamic change of microbial communities. The results indicated that:(1) Relative to surface wiping method, washing method was more suitable for the sampling of microbes on the surface of tobacco leaves; (2) Dry-ball temperature set and wet-ball temperature degradation flue-curing procedure was more favorable for maintaining the microbial diversity of tobaccos; (3) Relative to bacteria of the tobaccos, the succession rule of the fungal communities in tobaccos was relatively steady; (4)Compared with bacterial community diversity, the fungal community diversity presented an obvious negative correlation with temperature and humidity during the flue-curing process. (5) The function of bacterial communities in tobaccos matched with the material transformation law of tobaccos, having a direct correlation on the flue-curing process. In short, Dry-ball temperature set and wet-ball temperature degradation flue-curing procedure can more favorably maintain the microbial diversity of tobaccos; moreover, the function of the tobacco system involved in microbes in tobaccos was closely related to the material transformation law of tobaccos in the flue-curing process. It validated that the bacteria in tobaccos play an important role in the flue-curing process of tobaccos.

Response of Phenylpropanoid Pathway and the Role of Polyphenols in Plants under Abiotic Stress

Phenolic compounds are an important class of plant secondary metabolites which play crucial physiological roles throughout the plant life cycle. Phenolics are produced under optimal and suboptimal conditions in plants and play key roles in developmental processes like cell division, hormonal regulation, photosynthetic activity, nutrient mineralization, and reproduction. Plants exhibit increased synthesis of polyphenols such as phenolic acids and flavonoids under abiotic stress conditions, which help the plant to cope with environmental constraints. Phenylpropanoid biosynthetic pathway is activated under abiotic stress conditions (drought, heavy metal, salinity, high/low temperature, and ultraviolet radiations) resulting in accumulation of various phenolic compounds which, among other roles, have the potential to scavenge harmful reactive oxygen species. Deepening the research focuses on the phenolic responses to abiotic stress is of great interest for the scientific community. In the present article, we discuss the biochemical and molecular mechanisms related to the activation of phenylpropanoid metabolism and we describe phenolic-mediated stress tolerance in plants. An attempt has been made to provide updated and brand-new information about the response of phenolics under a challenging environment.

Defense potential of secondary metabolites in medicinal plants under UV-B stress

Ultraviolet-B (UV-B) radiation has, for many decades now, been widely studied with respect to its consequences on plant and animal health. Though according to NASA, the ozone hole is on its way to recovery, it will still be a considerable time before UV-B levels reach pre-industrial limits. Thus, for the present, excessive UV-B reaching the Earth is a cause for concern, and UV-B related human ailments are on the rise. Plants produce various secondary metabolites as one of the defense strategies under UV-B. They provide photoprotection via their UV-B screening effects and by quenching the reactive oxygen- and nitrogen species produced under UV-B influence. These properties of plant secondary metabolites (PSMs) are being increasingly recognized and made use of in sunscreens and cosmetics, and pharma- and nutraceuticals are gradually becoming a part of the regular diet. Secondary metabolites derived from medicinal plants (alkaloids, terpenoids, and phenolics) are a source of pharmaceuticals, nutraceuticals, as well as more rigorously tested and regulated drugs. These metabolites have been implicated in providing protection not only to plants under the influence of UV-B, but also to animals/animal cell lines, when the innate defenses in the latter are not adequate under UV-B-induced damage. The present review focuses on the defense potential of secondary metabolites derived from medicinal plants in both plants and animals. In plants, the concentrations of the alkaloids, terpenes/terpenoids, and phenolics have been discussed under UV-B irradiation as well as the fate of the genes and enzymes involved in their biosynthetic pathways. Their role in providing protection to animal models subjected to UV-B has been subsequently elucidated. Finally, we discuss the possible futuristic scenarios and implications for plant, animal, and human health pertaining to the defense potential of these secondary metabolites under UV-B radiation-mediated damages.

Species composition and diversity of ground bryophytes across a forest edge-to-interior gradient

Understanding diversity patterns and community structure of bryophytes will help integrate nature conservation at multiple biotic-group levels. We conducted a survey of ground bryophytes in a subtropical forest along an edge-to-interior gradient in South China. We recorded 11 liverwort species from 10 genera of seven families, and 26 moss species from 23 genera of 16 families in three transects. A two-way cluster analysis detected the environmental gradient between the forest edge and forest interior for bryophytes with habitat specificity. Functional diversity of bryophytes differed significantly across an edge-to-interior gradient. The range and median in both structural and functional diversity decreased remarkably from the forest edge to the interior. Multi-response permutation procedures showed significant differences in species composition between the forest-edge and forest-interior, and between the intermediate and forest-interior transects. Seven species were detected with a significant indicator value for indicating environmental conditions in the forest edge, while only one such species was found indicative of the intermediate transect. Our results demonstrate that remarkable edge effects exist for species composition and functional diversity patterns, and the forest edge is a marginal habitat with high biotic heterogeneity. Furthermore, functional diversity metrics are more sensitive to the edge effect than species diversity.

Interactive effects of supplemental ultraviolet-B radiation and indole-3-acetic acid on Coleus forskohlii Briq.: Alterations in morphological-, physiological-, and biochemical characteristics and essential oil content

Ultraviolet (UV)-B radiation and the growth hormone indole-3-acetic acid (IAA) have been known to cause various changes in plants at morphological and physiological levels as individual entities, but their interactive effects on the overall plant performance remain practically unknown. The present study was conducted under near-natural field conditions to evaluate the effects of supplemental (s)-UV-B (ambient+3.6kJm^-2day^-1) treatment alone, and in combination with two doses of IAA (200ppm and 400ppm) exogenously applied as foliar spray on various growth-, morphological-, physiological-, and biochemical parameters of an indigenous medicinal plant, Coleus forskohlii. Under s-UV-B, the plant growth and morphology were adversely affected (along with reductions in protein- and chlorophyll contents) with concomitant increase in secondary metabolites (as substantiated by an increase in the activities of various enzymes of the phenylpropanoid pathway) and cumulative antioxidative potential (CAP), suggesting the plant's capability of adaptive resilience against UV-B. The essential oil content of the plant was, however, compromised reducing its pharmaceutical value. IAA application at both doses led to a reversal in the effects caused by s-UV-B radiation alone; both the plant growth as well as the essential oil content improved, especially at the higher IAA dose, suggesting its ameliorative role against UV-B induced oxidative stress, and also in improving the plant's medicinal value.

Abietane-type diterpenoids from the roots of Caryopteris mongolica and their cholinesterase inhibitory activities

Eleven abietane-type diterpenoids and two known abietanes were isolated from the roots of Caryopteris mongolica, and their structures were characterized. The absolute configurations at C-5 and C-10 were determined from the NMR data, including from the nuclear Overhauser effect and CD spectra, and the absolute configuration of C-16 in the hydroxypropyl group was determined via a modified Mosher's method. Furthermore, the previously unknown absolute configuration of the C-15 of cyrtophyllone B was determined to be in an R-configuration using X-ray crystallography. To estimate the preventive effects of the isolates for neurodegenerative disease development, their inhibitory activities against acetylcholinesterase (AChE) from human erythrocytes and butyrylcholinesterase (BChE) from horse serum were evaluated.

Impact of UV-B on drought- or cadmium-induced changes in the fatty acid composition of membrane lipid fractions in wheat

UV-B radiation may have either a positive or negative impact under the same conditions in wheat, depending on the type of secondary abiotic stressor: Cd or drought. Supplemental UV-B prevented the wilting and leaf rolling induced by PEG treatment. In contrast, combined UV-B and Cd treatment resulted in pronounced oxidative stress. The opposite effect of UV-B radiation in the case of drought or cadmium stress may be related to the alteration induced in the fatty acid composition. UV-B caused changes in the unsaturation of leaf phosphatidylglycerol fractions, and the accumulation of flavonoid in the leaves may prevent the stress induced by subsequent drought treatment. However it resulted in pronounced injury despite the increased flavonoid content in roots exposed to Cd. This was manifested in a drastic decrease in the unsaturation of the leaf monogalactosyldiacylglycerol and the root phosphatidylglycerol and digalactosyldiacylglycerol fractions. Data on the flavonoid content and fatty acid composition showed that oxidative stress was induced by drought in the leaves, by Cd in the roots, and interestingly, by UV-B radiation in both the leaves and roots. The additive effect of the combined stresses was also detected in the roots. The results presented here suggest a relationship between the capacity of the plant to remodel the fatty acid composition and its resistance to various stress factors.

Influence of UV radiation on chlorophyll, and antioxidant enzymes of wetland plants in different types of constructed wetland

A surface- and vertical subsurface-flow-constructed wetland were designed to study the response of chlorophyll and antioxidant enzymes to elevated UV radiation in three types of wetland plants (Canna indica, Phragmites austrail, and Typha augustifolia). Results showed that (1) chlorophyll content of C. indica, P. austrail, and T. augustifolia in the constructed wetland was significantly lower where UV radiation was increased by 10 and 20 % above ambient solar level than in treatment with ambient solar UV radiation (p < 0.05). (2) The malondialdehyde (MDA) content, guaiacol peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activities of wetland plants increased with elevated UV radiation intensity. (3) The increased rate of MDA, SOD, POD, and CAT activities of C. indica, P. australis, and T. angustifolia by elevated UV radiation of 10 % was higher in vertical subsurface-flow-constructed wetland than in surface-flow-constructed wetland. The sensitivity of MDA, SOD, POD, and CAT activities of C. indica, P. austrail, and T. augustifolia to the elevated UV radiation was lower in surface-flow-constructed wetland than in the vertical subsurface-flow-constructed wetland, which was related to a reduction in UV radiation intensity through the dissolved organic carbon and suspended matter in the water. C. indica had the highest SOD and POD activities, which implied it is more sensitive to enhanced UV radiation. Therefore, different wetland plants had different antioxidant enzymes by elevated UV radiation, which were more sensitive in vertical subsurface-flow-constructed wetland than in surface-flow-constructed wetland.

Short-term UV-B dose stimulates production of protective metabolites in Matricaria chamomilla leaves

Physiological response of two cultivars of Matricaria chamomilla plants on UV irradiation was studied. The impact of used short-time UV dose was evaluated in three time points; 2, 24 and 48 h after irradiation. Used UV irradiation immediately resulted in changes in plant oxidative status monitored as increased concentration of H2 O2 . Decrease in chlorophyll a and b indicated the impact on photosynthetic apparatus. For phenolic secondary metabolites, an increase in total soluble phenols and AlCl3 -reactive flavonols was observed. The activity of main phenolic enzyme, phenylalanine ammonia-lyase, increased with time after irradiation. Significant changes, mainly decreasing trends, in the content of free coumarins and their glycosidic precursors were observed. Enhanced accumulation in chlorogenic and 1,5-dicaffeoylquinic acid and in (Z)-isoform of dicycloethers was detected. From these results, the redirecting precursors of coumarin biosynthesis to biosynthesis of substances with higher antioxidative potential can be assumed. Different reactions in diploid and tetraploid plants were recorded, too.