UV-B induces the expression of flavonoid biosynthetic pathways in blueberry (Vaccinium corymbosum) calli

Genetic analysis and fine mapping reveal that AhRt3, which encodes an anthocyanin reductase, is responsible for red testa in cultivated peanuts

KEY MESSAGE

AhRt3, which governs the red testa of peanut, was narrowed down to a 125.30 kb region, and one gene encoding anthocyanin reductase was identified as the putative candidate gene. Testa color is a special characteristic of peanuts (Arachis hypogaea L.), and those with dark testa have been focused on recent years owing to their high-anthocyanin content and increased antioxidant nutritional value. However, the genetic mechanisms underlying this trait remain limited. To identify the gene responsible for the red testa color in peanuts, an F2 population was constructed by crossing YH91 (pink testa) with JHT1 (red testa). Genetic analysis revealed that the red testa was controlled by a single dominant gene named AhRt3 (Arachis hypogaea Red Testa 3). Through bulked segregant analysis sequencing, AhRt3 was preliminarily mapped to the chromosome Arahy.03 and subsequently narrowed to a 125.30 kb genomic region containing 12 potential candidate genes. RNA-seq analysis revealed that 4,880 genes were differentially expressed in the seed testa, with only the candidate gene Arahy.W8TDEC exhibiting higher expression levels in JHT1 than in YH91. Additionally, sequence variation, functional annotation, and expression profiling confirmed that Arahy.W8TDEC, which encodes an anthocyanin reductase, may be a candidate gene for AhRt3. The structural variation involving an inversion between the sixth exon and the 3'UTR of Arahy.W8TDEC resulted in altered amino acids closely associated with the red testa phenotype in peanuts. In conclusion, this study highlights the role of a novel gene in regulating red testa and contributes valuable insights into the genetic basis of seed testa in peanuts.

Effect of UV-B stress on olive (Olea europaea L.) pollen tubes: A study of callose plug deposition and male germ unit integrity

While UV-B radiation is beneficial to plant growth, it can also cause adverse effects. The pollen tube, a key component of plant reproduction with a tip growth mechanism, is an excellent cellular model for understanding how environmental stressors such as UV-B radiation affect plant cell growth. This research investigated the effect of UV-B on olive pollen both before and after germination. Pollen grains were hydrated and exposed to UV-B radiation for 1 h. Pollen tube germination was then evaluated 4 and 24 h after exposure. To study the effect of UV-B radiation on developing pollen tubes, pollen was germinated for 4 h prior to 1 h of UV-B exposure. Pollen tube growth was evaluated by assessing the distribution of cell wall components, the distance between callose plugs and nuclei, and the distance between the male germ unit and the pollen tube tip. We also examined the accumulation of callose synthase. The results showed that UV-B radiation significantly inhibited the growth of pollen tubes, thereby preventing successful fertilization. The effect of UV-B exposure on pollen tube growth was mainly due to the alteration of position of callose plugs and the level of callose synthase in the pollen tube, potentially affecting its growth. In addition, UV-B radiation affected the movement and integrity of the male germ unit, a critical element for successful fertilization. This research sheds light on how UV-B radiation affects the growth of pollen tubes and highlights the need for further research into the effects of UV-B radiation on plant cells and plant reproduction.

An integrated transcriptome, metabolome, and microbiome dataset of Populus under nutrient-poor conditions

The rhizosphere microbiota recruited by plants contributes significantly to maintaining host productivity and resisting stress. However, the genetic mechanisms by which plants regulate this recruitment process remain largely unclear. Here, we generated a comprehensive dataset, including 27 root transcriptomes, 27 root metabolomes, and 54 bulk or rhizosphere soil 16S rRNA amplicons across nine poplar species from four sections grown in nutrient-poor natural soil, along with eleven growth phenotype data. We provided a thorough description of this dataset, followed by a comprehensive co-expression network analysis example that broke down the wall of the four-way relationship between plant gene-metabolite-microbe-phenotype, thus identifying the links between plant gene expression, metabolite accumulation, growth behavior, and rhizosphere microbiome variation under nutrient-poor conditions. Overall, this dataset enhances our understanding of plant and microbe interactions, offering valuable strategies and novel insights for resolving how plants regulate rhizosphere microbial compositions and functions, thereby improving host fitness, which will benefit future research.

Molecular underpinnings of EbMYBP1-mediated plant defense against UV-B radiation

MYB transcription factors play an important role in the response of plants to abiotic stress. The flavonoids found in Erigeron breviscapus have significant anti-inflammatory and cardiovascular therapeutic effects. It has been discovered that EbMYBP1, a gene cloned from E.breviscapus, positively regulates flavonoid synthesis. However, it is uncertain whether EbMYBP1-OE directly responds to ultraviolet B (UV-B) by increasing flavonoids accumulation. Here, an integrated metabolome-transcriptome analysis revealed an important role for EbMYBP1 in transgenic tobacco seeds in response to UV-B. The role of EbMYBP1 under UV-B has been examined. The results showed that a higher level of UV-B tolerance was observed in seedlings and leaves of EbMYBP1-OE lines (OE8, OE10, OE15) than in wild-type line (WT), identifying several flavonoid biosynthesis genes and metabolites. Compared with WT, a significant decrease in reactive oxygen species (ROS), an increase in antioxidant enzyme expression, and significant induction of genes involved in flavonoids synthesis, UV-B response, and ROS was observed after UV-B treatment in EbMYBP1-OE lines. Overall, EbMYBP1 modulates ROS scavengers and upregulates stress response genes to increase UV-B tolerance.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-025-01598-y.

Comparative role of betalains and other key antioxidant metabolites in the photoprotection against acute exposure to UV-B radiation in Chenopodium quinoa and C. berlandieri seedlings

Chenopodium quinoa Willd. is a betalainic crop with remarkable tolerance to extreme environmental conditions. Despite numerous varieties grow at high altitudes, where UV-B radiation is intense, research on the effects of UV-B stress on this and related species is very scarce. In the present work we aimed to determine whether UV-B radiation induces the production of betalains, and evaluated the role of these pigments and other key antioxidants in preventing oxidative damage, in seedlings of C. quinoa (ecotypes CICA and Villarrica) and its close relative C. berlandieri Moq., grown in darkness and after exposure to an acute pulse of UV-B radiation (24 h, 2.5 W m-2). UV-B significantly increased MDA accumulation and induced the production of betalains (particularly betacyanins), polyphenols and UV-B-absorbing compounds in all seedlings tested. The activity of antioxidant enzymes showed comparatively minor changes, with the exception of GPOX which consistently decreased after UV-B irradiation. The degree of oxidative damage was not correlated to the concentration of betalains present in the tissues at the end of the treatment. However, when pigment synthesis was stimulated by short white light pulses prior to UV-B irradiation, the increase in MDA levels could be prevented in C. berlandieri seedlings despite no major changes occurred in most of the remaining metabolites evaluated, suggesting that betalains have an important role in controlling oxidative damage in this species. In contrast, the presence of high levels of polyphenolic compounds rather than the accumulation of betalains contributed to improved UV-B tolerance in C. quinoa seedlings.

Combining Abiotic Stresses as a Low-Cost Strategy for Increasing the Phenolic Content in Apple Agro-Industrial By-Products

The circular economy approach offers innovative solutions for valorizing apple by-products through biofortification strategies transforming waste into high-value products and reducing environmental impact. This study evaluates innovative solutions for valorizing Granny Smith apple peel (RM) through biofortification in phenolic compounds using individual or combined abiotic stresses, like wounding stress and ultraviolet A (UVA) radiation. The effects of cutting type (Ct) [whole (C1), 5 mm (C2), 1.5 mm (C3)], storage temperature (ST) [20, 15, 10, 5 °C], and storage time (TM) [0, 12, 24, 48, 72 h] on phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) activity, total phenolic content (TPC), and phenolic profiles were studied first. The results show that higher stress intensity (C3, 15 °C, 48 h) significantly enhanced secondary metabolism, leading to notable increases in PAL activity (1201%), PPO activity (308%), TPC levels (108-118%), and Procyanidin B2 (PACB2, 22%), the predominant phenolic compound. These changes were critical for improving the bioactive properties and antioxidant potential of RM. The second assay combined wounding stress (same levels of Ct and ST of previous assay, TM: 56 h) with UVA radiation (UVA-D) [0, 86.4 KJ m-2, 172.8 KJ m-2], determining the optimal conditions (C3, UVA-D 66 KJ m-2, 17 °C) for maximizing PAL activity (0.12-0.20 ΔA h⁻1 mg⁻1), and TPC (3.3 g GAE kg⁻1). This study demonstrates the potential of combined abiotic stresses as cost-effective scalable tools to biofortify RM, promoting the sustainable and value-added utilization of agro-industrial by-products.

Identification and characteristics of differentially expressed genes under UV-B stress in Gossypium hirsutum

Objective

This study aimed to screen the differentially expressed genes (DEGs) of Gossypium hirsutum under UV-B stress and identify the significant pathways based on gene enrichment analysis results.

Methods

In this study, the allotetraploid crop G. hirsutum was used to examine changes in various physiological indexes under UV-B stress, and screened out all DEGs under UV-B stress (16 kJ m-2 d-1) based on six leaf transcriptomes. The main enrichment pathways of DEGs were analyzed according to gene annotation. Finally, we predicted the regulatory genes of phenylpropanoid pathway under UV-B stress by co-expression network analysis, and selected GhMYB4 for verification.

Results

Gene annotation analysis revealed that DEGs were predominantly enriched in pathways related to photosynthesis and secondary metabolism. Further analysis revealed that UV-B stress impaired photosynthesis mainly by damaging photosystem II (PSII) and inhibiting electron transport, whereas G. hirsutum responded to UV-B stress by synthesizing secondary metabolites such as anthocyanins and lignin. We selected the regulatory genes GhMYB4 for verification. It was found to be an anthocyanin negative regulator in response to UV-B stress.

Conclusions

UV-B stress impaired photosynthesis mainly by damaging photosystem II (PSII) and inhibiting electron transport, whereas G. hirsutum responded to UV-B stress by synthesizing secondary metabolites such as anthocyanins and lignin.

The effect of supplemental LED lighting in the range of UV, blue, and red wavelengths at different ratios on the accumulation of phenolic compounds in pak choi and swiss chard

Phenolic compounds are known for their health-promoting effects on humans. Pak choi (Brassica rapa ssp. chinensis) and Swiss chard (Beta vulgaris subsp. vulgaris) are used here as model plants, as they are eaten raw as baby leaf lettuce and differ in their phenolic compound profile while showing similar morphology. In a greenhouse an artificial light source with UV-B (215 mW m-2), blue (104 μmol m-2 s-1) and red (245 μmol m-2 s-1) LEDs was implemented to increase phenolic compounds during the last days before harvest. Pak choi shows an increase or trend towards an increase in the monoacylated triglycosides of kaempferol and quercetin after 4 days of irradiation for 4 h each. For example kaempferol-3-caffeoyl-sophoroside-7-glucoside was increased at low PAR values in the third run and red-dominated light treatment by up to 120 %. In addition, it was observed that the red variety 'Amur' has higher concentrations of quercetin glycosides which were increased often. In swiss chard, on the other hand, there was only a sporadic increase in vitexin glycosides. Despite very different concentrations in some samples, 2″-glucosyl-vitexin and 2″-glucosyl-6″-malonyl-vitexin showed significant increases of up to 350 % in the two chard varieties Lukullus and Rhubarb chard. The results suggest that the exposure time or intensity of UV-B radiation needs to be optimized for each species and has not yet consistently led to an increase but trends in phenolic compounds and in antioxidant activity in this study.

Variability of plant transcriptomic responses under stress acclimation: a review from high throughput studies

Plant transcriptomes are complex entities shaped spatially and temporally by a multitude of stressors. The aim of this review was to summarize the most relevant transcriptomic responses to selected abiotic (UV radiation, chemical compounds, drought, suboptimal temperature) and biotic (bacteria, fungi, viruses, viroids) stress conditions in a variety of plant species, including model species, crops, and medicinal plants. Selected basic and applicative studies employing RNA-seq from various sequencing platforms and single-cell RNA-seq were involved. The transcriptomic responsiveness of various plant species and the diversity of affected gene families were discussed. Under stress acclimation, plant transcriptomes respond particularly dynamically. Stress response involved both distinct, but also similar gene families, depending on the species, tissue, and the quality and dosage of the stressor. We also noted the over-representation of transcriptomic data for some plant organs. Studies on plant transcriptomes allow for a better understanding of response strategies to environmental conditions. Functional analyses reveal the multitude of stress-affected genes as well as acclimatory mechanisms and suggest metabolome diversity, particularly among medicinal species. Extensive characterization of transcriptomic responses to stress would result in the development of new cultivars that would cope with stress more efficiently. These actions would include modern methodological tools, including advanced genetic engineering, as well as gene editing, especially for the expression of selected stress proteins in planta and for metabolic modifications that allow more efficient synthesis of secondary metabolites.

Metabolite and Transcriptome Profiling Analysis Provides New Insights into the Distinctive Effects of Exogenous Melatonin on Flavonoids Biosynthesis in Rosa rugosa

Although the petals of Rosa rugosa are rich in flavonoids and their bioactivity has a significant impact on human health, the flavonoid content decreases during flower development. In this study, R. rugosa 'Feng hua' was used to investigate the effects of the melatonin foliar spray on enhancing the quality of rose by focusing on major flavonoids. The results showed that the contents of total flavonoids in rose petals at the full bloom stage induced by melatonin obeyed a bell-shaped curve, with a maximum at 0.3 mM, indicating the concentration-dependent up-regulation of flavonoid biosynthesis. In the treatment with 0.3 mM melatonin, metabolomic analyses showed that the concentrations of ten main flavonoids were identified to be increased by melatonin induction, with high levels and increases observed in three flavonols and two anthocyanins. KEGG enrichment of transcriptomic analysis revealed a remarkable enrichment of DEGs in flavonoid and flavonol biosynthesis, such as Rr4CL, RrF3H, and RrANS. Furthermore, functional validation using virus-induced gene silencing technology demonstrated that Rr4CL3 is the crucial gene regulating flavonoid biosynthesis in response to the stimulant of melatonin. This study provides insights into the exogenous melatonin regulation mechanism of biosynthesis of flavonoids, thereby offering potential industrial applications.

The miR6445-NAC029 module regulates drought tolerance by regulating the expression of glutathione S-transferase U23 and reactive oxygen species scavenging in Populus

MicroRNAs are essential in plant development and stress resistance, but their specific roles in drought stress require further investigation. Here, we have uncovered that a Populus-specific microRNAs (miRNA), miR6445, targeting NAC (NAM, ATAF, and CUC) family genes, is involved in regulating drought tolerance of poplar. The expression level of miR6445 was significantly upregulated under drought stress; concomitantly, seven targeted NAC genes showed significant downregulation. Silencing the expression of miR6445 by short tandem target mimic technology significantly decreased the drought tolerance in poplar. Furthermore, 5' RACE experiments confirmed that miR6445 directly targeted NAC029. The overexpression lines of PtrNAC029 (OE-NAC029) showed increased sensitivity to drought compared with knockout lines (Crispr-NAC029), consistent with the drought-sensitive phenotype observed in miR6445-silenced strains. PtrNAC029 was further verified to directly bind to the promoters of glutathione S-transferase U23 (GSTU23) and inhibit its expression. Both Crispr-NAC029 and PtrGSTU23 overexpressing plants showed higher levels of PtrGSTU23 transcript and GST activity while accumulating less reactive oxygen species (ROS). Moreover, poplars overexpressing GSTU23 demonstrated enhanced drought tolerance. Taken together, our research reveals the crucial role of the miR6445-NAC029-GSTU23 module in enhancing poplar drought tolerance by regulating ROS homeostasis. This finding provides new molecular targets for improving the drought resistance of trees.

Multi-omics analysis reveals key regulatory defense pathways and genes involved in salt tolerance of rose plants

Salinity stress causes serious damage to crops worldwide, limiting plant production. However, the metabolic and molecular mechanisms underlying the response to salt stress in rose (Rosa spp.) remain poorly studied. We therefore performed a multi-omics investigation of Rosa hybrida cv. Jardin de Granville (JDG) and Rosa damascena Mill. (DMS) under salt stress to determine the mechanisms underlying rose adaptability to salinity stress. Salt treatment of both JDG and DMS led to the buildup of reactive oxygen species (H2O2). Palisade tissue was more severely damaged in DMS than in JDG, while the relative electrolyte permeability was lower and the soluble protein content was higher in JDG than in DMS. Metabolome profiling revealed significant alterations in phenolic acid, lipids, and flavonoid metabolite levels in JDG and DMS under salt stress. Proteome analysis identified enrichment of flavone and flavonol pathways in JDG under salt stress. RNA sequencing showed that salt stress influenced primary metabolism in DMS, whereas it substantially affected secondary metabolism in JDG. Integrating these datasets revealed that the phenylpropane pathway, especially the flavonoid pathway, is strongly enhanced in rose under salt stress. Consistent with this, weighted gene coexpression network analysis (WGCNA) identified the key regulatory gene chalcone synthase 1 (CHS1), which is important in the phenylpropane pathway. Moreover, luciferase assays indicated that the bHLH74 transcription factor binds to the CHS1 promoter to block its transcription. These results clarify the role of the phenylpropane pathway, especially flavonoid and flavonol metabolism, in the response to salt stress in rose.

Multifaceted roles of WRKY transcription factors in abiotic stress and flavonoid biosynthesis

Increasing biotic and abiotic stresses are seriously impeding the growth and yield of staple crops and threatening global food security. As one of the largest classes of regulators in vascular plants, WRKY transcription factors play critical roles governing flavonoid biosynthesis during stress responses. By binding major W-box cis-elements (TGACCA/T) in target promoters, WRKYs modulate diverse signaling pathways. In this review, we optimized existing WRKY phylogenetic trees by incorporating additional plant species with WRKY proteins implicated in stress tolerance and flavonoid regulation. Based on the improved frameworks and documented results, we aim to deduce unifying themes of distinct WRKY subfamilies governing specific stress responses and flavonoid metabolism. These analyses will generate experimentally testable hypotheses regarding the putative functions of uncharacterized WRKY homologs in tuning flavonoid accumulation to enhance stress resilience.

Enhanced UV-B Radiation in Potato Stems and Leaves Promotes the Accumulation of Anthocyanins in Tubers

Enhanced ultraviolet-B (UV-B) radiation promotes anthocyanin biosynthesis in leaves, flowers and fruits of plants. However, the effects and underlying mechanisms of enhanced UV-B radiation on the accumulation of anthocyanins in the tubers of potatoes (Solanum tuberosum L.) remain unclear. Herein, reciprocal grafting experiments were first conducted using colored and uncolored potatoes, demonstrating that the anthocyanins in potato tubers were synthesized in situ, and not transported from the leaves to the tubers. Furthermore, the enhanced UV-B radiation (2.5 kJ·m-2·d-1) on potato stems and leaves significantly increased the contents of total anthocyanin and monomeric pelargonidin and peonidin in the red-fleshed potato '21-1' tubers, compared to the untreated control. A comparative transcriptomic analysis showed that there were 2139 differentially expressed genes (DEGs) under UV-B treatment in comparison to the control, including 1724 up-regulated and 415 down-regulated genes. The anthocyanin-related enzymatic genes in the tubers such as PAL, C4H, 4CL, CHS, CHI, F3H, F3'5'H, ANS, UFGTs, and GSTs were up-regulated under UV-B treatment, except for a down-regulated F3'H. A known anthocyanin-related transcription factor StbHLH1 also showed a significantly higher expression level under UV-B treatment. Moreover, six differentially expressed MYB transcription factors were remarkably correlated to almost all anthocyanin-related enzymatic genes. Additionally, a DEGs enrichment analysis suggested that jasmonic acid might be a potential UV-B signaling molecule involved in the UV-B-induced tuber biosynthesis of anthocyanin. These results indicated that enhanced UV-B radiation in potato stems and leaves induced anthocyanin accumulation in the tubers by regulating the enzymatic genes and transcription factors involved in anthocyanin biosynthesis. This study provides novel insights into the mechanisms of enhanced UV-B radiation that regulate the anthocyanin biosynthesis in potato tubers.

Genome-Wide Analysis of the Universal Stress Protein Gene Family in Blueberry and Their Transcriptional Responses to UV-B Irradiation and Abscisic Acid

Universal stress proteins (USPs) play essential roles in plant development, hormonal regulation, and abiotic stress responses. However, the characteristics and functional divergence of USP family members have not been studied in blueberry (Vaccinium corymbosum). In this study, we identified 72 VcUSP genes from the Genome Database for Vaccinium. These VcUSPs could be divided into five groups based on their phylogenetic relationships. VcUSPs from groups Ⅰ, Ⅳ, and Ⅴ each possess one UspA domain; group Ⅰ proteins also contain an ATP-binding site that is not present in group Ⅳ and Ⅴ proteins. Groups Ⅱ and Ⅲ include more complex proteins possessing one to three UspA domains and UspE or UspF domains. Prediction of cis-regulatory elements in the upstream sequences of VcUSP genes indicated that their protein products are likely involved in phytohormone signaling pathways and abiotic stress responses. Analysis of RNA deep sequencing data showed that 21 and 7 VcUSP genes were differentially expressed in response to UV-B radiation and exogenous abscisic acid (ABA) treatments, respectively. VcUSP41 and VcUSP68 expressions responded to both treatments, and their encoded proteins may integrate the UV-B and ABA signaling pathways. Weighted gene co-expression network analysis revealed that VcUSP22, VcUSP26, VcUSP67, VcUSP68, and VcUSP41 were co-expressed with many transcription factor genes, most of which encode members of the MYB, WRKY, zinc finger, bHLH, and AP2 families, and may be involved in plant hormone signal transduction, circadian rhythms, the MAPK signaling pathway, and UV-B-induced flavonoid biosynthesis under UV-B and exogenous ABA treatments. Our study provides a useful reference for the further functional analysis of VcUSP genes and blueberry molecular breeding.

Genome-wide analysis of blueberry B-box family genes and identification of members activated by abiotic stress

BACKGROUND

B-box (BBX) proteins play important roles in regulating plant growth, development, and abiotic stress responses. BBX family genes have been identified and functionally characterized in many plant species, but little is known about the BBX family in blueberry (Vaccinium corymbosum).

RESULT

In this study, we identified 23 VcBBX genes from the Genome Database for Vaccinium (GDV). These VcBBXs can be divided into five clades based on gene structures and conserved domains in their encoded proteins. The prediction of cis-acting elements in the upstream sequences of VcBBX genes and protein-protein interactions indicated that VcBBX proteins are likely involved in phytohormone signaling pathways and abiotic stress responses. Analysis of transcriptome deep sequencing (RNA-seq) data showed that VcBBX genes exhibited organ-specific expression pattern and 11 VcBBX genes respond to ultraviolet B (UV-B) radiation. The co-expression analysis revealed that the encoded 11 VcBBX proteins act as bridges integrating UV-B and phytohormone signaling pathways in blueberry under UV-B radiation. Reverse-transcription quantitative PCR (RT-qPCR) analysis showed that most VcBBX genes respond to drought, salt, and cold stress. Among VcBBX proteins, VcBBX24 is highly expressed in all the organs, not only responds to abiotic stress, but it also interacts with proteins in UV-B and phytohormone signaling pathways, as revealed by computational analysis and co-expression analysis, and might be an important regulator integrating abiotic stress and phytohormone signaling networks.

CONCLUSIONS

Twenty-three VcBBX genes were identified in blueberry, in which, 11 VcBBX genes respond to UV-B radiation, and act as bridges integrating UV-B and phytohormone signaling pathways according to RNA-seq data. The expression patterns under abiotic stress suggested that the functional roles of most VcBBX genes respose to drought, salt, and cold stress. Our study provides a useful reference for functional analysis of VcBBX genes and for improving abiotic stress tolerance in blueberry.

Rice Mitogen-Activated Protein Kinase regulates serotonin accumulation and interacts with cell cycle regulators under prolonged UV-B exposure

Stress conditions such as UV-B exposure activates MAPKs in Arabidopsis and rice. UV-B radiation is hazardous to plant as it causes photosystem disruption, DNA damage and ROS generation. Here we report its effect on biological pathways by studying the global changes in transcript profile in rice seedling exposed to UV-B radiation for 1 h and 16 h. Short UV-B exposure (1 h) led to moderate changes, while a drastic change in transcript landscape was observed after long term UV-B exposure (16 h) in rice seedlings. Prolonged UV-B exposure negatively impacts the expression of cell cycle regulating genes and several other metabolic pathways in developing seedlings. MAP kinase signaling cascade gets activated upon UV-B exposure similar to reports in Arabidopsis indicating conservation of its function in both dicot and monocot. Expression analysis in inducible overexpression transgenic lines of MPK3 and MPK6 shows higher transcript abundance of phytoalexin biosynthesis gene like Oryzalexin D synthase and Momilactone A synthase, along with serotonin biosynthesis genes. An accumulation of serotonin was observed upon UV-B exposure and its abundance positively correlates with the MPK3 and MPK6 transcript level in the respective over-expression lines. Interestingly, multiple cell cycle inhibitor proteins including WEE1 and SMR1 interact with MPK3 and MPK6 thus, implying a major role of this pathway in cell cycle regulation under stress condition. Overall overexpression of MPK3 and MPK6 found to be detrimental for rice as overexpression lines shows higher cell death and compromised tolerance to UV-B.

Advances in the study of the function and mechanism of the action of flavonoids in plants under environmental stresses

MAIN CONCLUSION

This review summarizes the anti-stress effects of flavonoids in plants and highlights its role in the regulation of polar auxin transport and free radical scavenging mechanism. As secondary metabolites widely present in plants, flavonoids play a vital function in plant growth, but also in resistance to stresses. This review introduces the classification, structure and synthetic pathways of flavonoids. The effects of flavonoids in plant stress resistance were enumerated, and the mechanism of flavonoids in plant stress resistance was discussed in detail. It is clarified that plants under stress accumulate flavonoids by regulating the expression of flavonoid synthase genes. It was also determined that the synthesized flavonoids are transported in plants through three pathways: membrane transport proteins, vesicles, and bound to glutathione S-transferase (GST). At the same time, the paper explores that flavonoids regulate polar auxin transport (PAT) by acting on the auxin export carrier PIN-FORMED (PIN) in the form of ATP-binding cassette subfamily B/P-glycoprotein (ABCB/PGP) transporter, which can help plants to respond in a more dominant form to stress. We have demonstrated that the number and location of hydroxyl groups in the structure of flavonoids can determine their free radical scavenging ability and also elucidated the mechanism by which flavonoids exert free radical removal in cells. We also identified flavonoids as signaling molecules to promote rhizobial nodulation and colonization of arbuscular mycorrhizal fungi (AMF) to enhance plant-microbial symbiosis in defense to stresses. Given all this knowledge, we can foresee that the in-depth study of flavonoids will be an essential way to reveal plant tolerance and enhance plant stress resistance.

MYB pathways that regulate UV-B-induced anthocyanin biosynthesis in blueberry (Vaccinium corymbosum)

Ultraviolet-B (UV-B) promotes anthocyanin accumulation and improves fruit quality in plants. To explore the underlying network of MYB transcription factors that regulates UV-B-induced anthocyanin biosynthesis in blueberry (Vaccinium corymbosum), we analyzed the response of MYB transcription factor genes to UV-B treatment. Transcriptome sequencing analysis revealed that VcMYBA2 and VcMYB114 expression were upregulated and were positively correlated with the expression of anthocyanin structural genes under UV-B radiation according to weighted gene co-expression network analysis (WGCNA) data. The VcUVR8-VcCOP1-VcHY5 pathway perceives UV-B signals and promotes the expression of anthocyanin structural genes by upregulating VcMYBA2 and VcMYB114 or by regulating the VcBBXs-VcMYB pathway, ultimately promoting anthocyanin accumulation. By contrast, VcMYB4a and VcUSP1 were downregulated under UV-B treatment, and VcMYB4a expression was negatively correlated with that of anthocyanin biosynthesis genes in response to UV-B. Analysis of VcMYB4a-overexpressing and wild-type blueberry calli exposed to UV-B radiation revealed that VcMYB4a represses UV-B-induced anthocyanin accumulation. Yeast one-hybrid and dual luciferase assays showed that the universal stress protein VcUSP1 directly bound to the promoter of VcMYB4a. These results suggest that the VcUSP1-VcMYB4a pathway negatively regulates UV-B-induced anthocyanin biosynthesis and provide insight into UV-B-induced anthocyanin biosynthesis.