Plant responses to UV-B radiation: signaling, acclimation and stress tolerance

Can autophagy enhance crop resilience to environmental stress?

Climate change imposes abiotic stress on plants, significantly threatening global agriculture and food security. This indicates a need to apply our understanding of plant stress responses to improve crop resilience to these threats. Stress damages critical cellular components such as mitochondria, chloroplasts and the endoplasmic reticulum. Left unmitigated, abiotic stress can lead to cell death, which typically decreases overall plant health and productivity. Autophagy is a catabolic process that maintains cellular homeostasis by degrading and recycling damaged and dysfunctional cell components and organelles. Importantly, autophagy promotes plant tolerance to a wide range of environmental stresses, and manipulation of autophagy may lead to improved stress resilience in crops. Here, we discuss recent advances in our understanding of how autophagy affects abiotic stress resistance. We discuss the function of autophagy in different abiotic stresses (including nutrient stress, salt stress, drought, heat, cold, hypoxia, light stress and combined stresses) and provide insights from functional and genome-wide transcriptomic studies. We also evaluate the potential to enhance crop survival and productivity in suboptimal environmental conditions by activating autophagy, emphasizing the importance of targeted manipulation of key genes involved in the autophagy pathway.This article is part of the theme issue 'Crops under stress: can we mitigate the impacts of climate change on agriculture and launch the 'Resilience Revolution'?'.

Engineering plant photoreceptors towards enhancing plant productivity

Light is a critical environmental factor that governs the growth and development of plants. Plants have specialised photoreceptor proteins, which allow them to sense both quality and quantity of light and drive a wide range of responses critical for optimising growth, resource use and adaptation to changes in environment. Understanding the role of these photoreceptors in plant biology has opened up potential avenues for engineering crops with enhanced productivity by engineering photoreceptor activity and/or action. The ability to manipulate plant genomes through genetic engineering and synthetic biology approaches offers the potential to unlock new agricultural innovations by fine-tuning photoreceptors or photoreceptor pathways that control plant traits of agronomic significance. Additionally, optogenetic tools which allow for precise, light-triggered control of plant responses are emerging as powerful technologies for real-time manipulation of plant cellular responses. As these technologies continue to develop, the integration of photoreceptor engineering and optogenetics into crop breeding programs could potentially revolutionise how plant researchers tackle challenges of plant productivity. Here we provide an overview on the roles of key photoreceptors in regulating agronomically important traits, the current state of plant photoreceptor engineering, the emerging use of optogenetics and synthetic biology, and the practical considerations of applying these approaches to crop improvement. This review seeks to highlight both opportunities and challenges in harnessing photoreceptor engineering approaches for enhancing plant productivity. In this review, we provide an overview on the roles of key photoreceptors in regulating agronomically important traits, the current state of plant photoreceptor engineering, the emerging use of optogenetics and synthetic biology, and the practical considerations of applying these approaches to crop improvement.

UV-B Irradiation Does Not Promote Flowering in Arabidopsis Despite Increased FT Expression

Various environmental factors control the plant flowering time. However, the specific effects of ultraviolet (UV)-B radiation on flowering remain unclear. UV-B irradiation delays flowering in Arabidopsis during short-day (SD) photoperiods. In contrast, UV-B irradiation causes a variety of flowering phenotypes during long-day (LD) photoperiods, including unchanged, delayed, and accelerated flowering. We hypothesized that variations in UV-B intensity are responsible for the phenotypic changes under LD photoperiods. Therefore, in this study, Arabidopsis plants were exposed to two distinct UV-B intensities: a low UV-B intensity that activates UVR8-dependent pathways and high UV-B intensity that activates both UVR8-dependent and -independent pathways. Under LD photoperiods, neither the wild-type (WT) nor the uvr8 mutant showed any change in flowering time at either UV-B irradiation intensity. Under the SD photoperiod, UV-B irradiation delayed WT flowering. The expression of flowering locus T (FT) increased after UV-B irradiation under the LD photoperiod in a UVR8-dependent manner. However, despite the increased expression of FT, expression levels of floral meristem identity genes in shoot apical meristem (SAM) were not increased by UV-B irradiation. As UV-B irradiation is known to suppress flowering in SAM in a UVR8-dependent manner, increase in FT expression induced by UV-B irradiation possibly antagonized the suppressive effect of UV-B irradiation. Overall, these results suggest that flowering phenotypes do not change with UV-B intensity but with the balance between the inhibitory and promotive effects of UVR8 activated by UV-B irradiation.

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.

Developing Light-Emitting Plants (LEPs) with SrAl2O4: Eu2+, Dy3+ by Using Pressure Infiltration, Optimal Conditions for Glowing and Plant Stress Response

Developing light-emitting plants (LEPs) using SrAl2O4 has been working for the past few years because SrAl2O4 is a phosphorescent material with long-lasting and bright glowing properties. The six plant species (Episcia cupreata, Tabebuia argentea, Syngonium hybrid, Mimusops elengi, Schefflera arboricola, and Pilea cadierei) were infused with SrAl2O4, which has a particle size of 2.7 µm. The E. cupreata exhibited the highest phosphorescence (a relative phosphorescence value of 36.93) compared to other plant species. The optimal pressure to infuse SrAl2O4 into the plant is 7 × 104 N/m2 exposed for 60 min while 17.5 g/L SrAl2O4 is the best concentration. After infusion, the plants did not show physical abnormalities. However, the amount of MDA and antioxidants in plants was increased. Based on metabolomics analysis, SrAl2O4 might stress plants, but plants might be able to respond by producing antioxidant compounds. Therefore, using SrAl2O4 to LEPs did not kill the plants and provided high light output.

Analysis of allohexaploid wheatgrass genome reveals its Y haplome origin in Triticeae and high-altitude adaptation

Phylogenetic origin of the Y haplome present in allopolyploid Triticeae species remains unknown. Here, we report the 10.47 Gb chromosome-scale genome of allohexaploid Elymus nutans (StStYYHH). Phylogenomic analyses reveal that the Y haplome is sister to the clade comprising V and Jv haplomes from Dasypyrum and Thinopyum. In addition, H haplome from the Hordeum-like ancestor, St haplome from the Pseudoroegneria-like ancestor and Y haplome are placed in the successively diverged clades. Resequencing data reveal the allopolyploid origins with St, Y, and H haplome combinations in Elymus. Population genomic analyses indicate that E. nutans has expanded from medium to high/low-altitude regions. Phenotype/environmental association analyses identify MAPKKK18 promoter mutations reducing its expression, aiding UV-B adaptation in high-altitude populations. These findings enhance understanding of allopolyploid evolution and aid in breeding forage and cereal crops through intergeneric hybridization within Triticeae.

Genome-wide identification and expression analysis of the ADH gene family in Artemisia annua L. under UV-B stress

ADHs are key genes that catalyze the interconversion between alcohols and aldehydes, which play crucial roles in plant adaptation to a range of abiotic stresses. However, the characterization and evolutionary pathways of ADH genes in the antimalarial plant Artemisia annua are still unclear. This study identified 49 ADH genes in A. annua and conducted a detailed analysis of their structural features, conserved motifs, and duplication types, revealing that tandem and dispersed duplications are the primary mechanisms of gene expansion. Evolutionary analysis of ADH genes between A. annua (AanADH) and A. argyi (AarADH) revealed dynamic changes, with 35 genes identified deriving from their most recent common ancestor in both species. ADH1, crucial for artemisinin production, had two copies in both species, expanding via dispersed duplication in A. annua but whole-genome duplication in A. argyi. CREs and WGCNA analysis suggested that AanADH genes may be regulated by UV-B stress. Following short-term UV-B treatment, 16 DEGs were identified, including ADH1 (AanADH6 and AanADH7), and these genes were significantly downregulated after two hours treatment (UV2h) and upregulated after four hours treatment (UV4h). The expression changes of these genes were further confirmed by GO enrichment analysis and qRT-PCR experiments. Overall, this study comprehensively characterized the ADH gene family in A. annua and systematically identified AanADH genes that were responsive to UV-B stress, providing a foundation for further research on their roles in abiotic stress responses.

CtWD40-6 enhances the UV-B tolerance of safflower by regulating flavonoid accumulation

Moderate UV-B promotes plant growth, but excessive UV-B inhibits plant development. The induction mechanism of how CtWD40-6 responds to UV-B is still unclear in safflower. Our results showed that CtWD40-6 is expressed at the top of safflower leaves and is strongly induced by UV-B. To further understand the function of the CtWD40-6 gene, we overexpressed the CtWD40-6 gene in safflower or Arabidopsis. First, different transgenic materials were treated with UV-B, and we found that the survival rate of plants overexpressing CtWD40-6 was significantly higher than that of the WT type. In contrast, the survival rate of wd40-6 mutant plants was significantly decreased compared with WT type. Then DAB, NBT and Trypan Blue staining were performed on different transgenic plants before and after UV-B treatment and the results showed that the staining of mutant and WT was significantly higher than that of overexpressing CtWD40-6. By comparing the data before and after UV-B stress, we found that the flavonoid content, antioxidant enzyme activity, chlorophyll content and photosynthetic rate of transgenic plants overexpressing CtWD40-6 were higher than those of WT and mutants, thereby obtaining better UV-B tolerance. Finally, we used yeast two-hybrid and luciferase complementation experiments to prove that CtWD40-6 increases the content of safflower flavonoids by interacting with CtANS1/CtCHS1/Ct4CL1/CtFLS1, thereby enhancing the plant's UV-B tolerance. The above results provide a theoretical basis for preliminary analysis of how safflower responds to UV-B stress through the transcriptional regulation of CtWD40-6.

Integrating Transcriptomics and Metabolomics to Comprehensively Analyze Phytohormone Regulatory Mechanisms in Rhododendron chrysanthum Pall. Under UV-B Radiation

In order to fully elucidate the roles and systems of phytohormones in UV-B radiation (UV-B) leaves of the Rhododendron chrysanthum Pall. (R. chrysanthum), we conducted a comprehensive analysis of how R. chrysanthum protects itself against UV-B using transcriptomic and metabolomic data. Transcript and metabolite profiles were generated by a combination of deep sequencing and LC-MS/MS (liquid chromatography-tandem mass spectrometry), respectively. Combined with physiological and biochemical assays, we studied compound accumulation, biosynthesis and expression of signaling genes of seven hormones and the effects of hormones on plant photosynthesis. The findings indicate that during leaf defense against UV-B, photosynthesis declined, the photosynthetic system was impaired and the concentration of salicylic acid (SA) hormones increased, whereas the contents of cytokinin (CK), abscisic acid (ABA), ethylene, auxin, jasmonic acid (JA) and gibberellins (GAs) continued to decrease. Finally, correlation tests between hormone content and genes were analyzed, and genes closely related to leaf resistance to UV-B were identified in seven pathways. These results will expand our understanding of the hormonal regulatory mechanisms of plant resistance to UV-B and at the same time lay the foundation for plant resistance to adversity stress.

Recent advances in UV-B signalling: interaction of proteins with the UVR8 photoreceptor

The UV RESISTANCE LOCUS 8 (UVR8) photoreceptor mediates many plant responses to UV-B and short wavelength UV-A light. UVR8 functions through interactions with other proteins which lead to extensive changes in gene expression. Interactions with particular proteins determine the nature of the response to UV-B. It is therefore important to understand the molecular basis of these interactions: how are different proteins able to bind to UVR8 and how is differential binding regulated? This concise review highlights recent developments in addressing these questions. Key advances are discussed with regard to: identification of proteins that interact with UVR8; the mechanism of UVR8 accumulation in the nucleus; the photoactivation of UVR8 monomer; the structural basis of interaction between UVR8 and CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) and REPRESSOR OF UV-B PHOTOMORPHOGENESIS (RUP) proteins; and the role of UVR8 phosphorylation in modulating interactions and responses to UV-B. Nevertheless, much remains to be understood, and the need to extend future research to the growing list of interactors is emphasized.

Agrivoltaics development progresses: From the perspective of photovoltaic impact on crops, soil ecology and climate

Agrivoltaics, the simultaneous use of land for both agriculture and photovoltaic (PV) energy production, has gained significant attention as a sustainable land-use strategy. This review investigates the progress of agrivoltaics from the perspective of its impacts on crops, soil ecology, and climate. First, the impacts of agrivoltaic systems on solar radiation were assessed, including soil humidity and, temperature dynamics, while considering the potential for changes in soil microbial communities. Second, how PV panels influence crop growth, yield, and quality through the modification of light distribution, temperature regulation, and soil humidity were explored. Lastly, the challenges and propose recommendations for optimizing the integration of agriculture and PV systems were addressed. This review aims to highlight the benefits and trade-offs of agrivoltaics, offering a roadmap for future research and implementation strategies to enhance the synergy between renewable energy production and sustainable agriculture.

The Role of Carnosic Acid in the UV-B Stress Resistance Signalling Pathway in Arabidopsis thaliana

Carnosic acid (CA) is recognized as an antioxidant that confers protection to plants against various forms of oxidative stress, including UV-B stress. However, limited research has been conducted to elucidate the molecular mechanisms underlying its defence against UV-B stress. In this study, we demonstrated that CA exhibits more efficacy compared to other antioxidants in UV-B resistance. Moreover, CA was found to enhance the accumulation of secondary metabolites in Arabidopsis leaves. Through the analysis of differentially expressed genes in response to UV-B stress with or without CA treatment, we uncovered that the exogenous application of CA effectively activates the flavonoid biosynthesis pathway in Arabidopsis to improve resistance of Arabidopsis to UV-B stress.

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.

Regulatory Mechanism of Exogenous ABA on Gibberellin Signaling and Antioxidant Responses in Rhododendron chrysanthum Pall. Under UV-B Stress

In the present work, we examined the effects of exogenous abscisic acid (ABA) under ultraviolet B (UV-B) exposure on gibberellin (GA) production, signaling, and antioxidant-related genes in Rhododendron chrysanthum Pall (R. chrysanthum). Using transcriptomics, acetylated proteomics, and widely targeted metabolomics, the effects of UV-B stress on R. chrysanthum and the regulatory effects of exogenous ABA on it were revealed from multiple perspectives. The findings revealed that R. chrysanthum's antioxidant enzyme genes were differentially expressed by UV-B radiation and were substantially enriched in the glutathione metabolic pathway. Exogenous ABA supplementation boosted plant resistance to UV-B damage and further enhanced the expression of antioxidant enzyme genes. Furthermore, under UV-B stress, glutathione reductase, glutathione peroxidase, and L-ascorbate peroxidase were found to be the primary antioxidant enzymes controlled by exogenous ABA. In addition, gibberellin content was altered due to UV-B and exogenous ABA treatments, with greater effects on GA3 and GA53. The acetylation proteomics study's outcomes disclosed that the three main oxidative enzymes' acetylation modifications were dramatically changed during UV-B exposure, which may have an impact on the antioxidant enzymes' functions and activities. The protective impact of exogenous ABA and gibberellin on R. chrysanthum's photosynthetic system was further established by measuring the parameters of chlorophyll fluorescence. This research offers a theoretical foundation for the development of breeding highly resistant plant varieties as well as fresh insights into how hormone levels and antioxidant systems are regulated by plants in response to UV-B damage.

Strigolactone modulates phenolic acid accumulation and thereby improves tolerance to UV-B stress in Rhododendron chrysanthum Pall

KEY MESSAGE

Multi-omics studies have shown that strigolactone modulates phenolic acid accumulation in the leaves of R. chrysanthum and can enable it to cope with UV-B stress. UV-B stress is an abiotic stress that plants will inevitably suffer during growth and can seriously affect the normal physiological state of plants. Strigolactone, a phytohormone, has been less studied and it is important to investigate its regulation of plant growth under UV-B radiation. In the present study, we investigated the changes in leaves of Rhododendron chrysanthum Pall. (R. chrysanthum) under UV-B radiation. The leaves of R. chrysanthum were collected for widely targeted metabolomics, hormonomics, transcriptomics, proteomics and acetylated proteomics assays. The results showed that the leaves of R. chrysanthum were able to produce a large amount of differential phenolic acids with antioxidant effects under UV-B stress, the content of strigolactone was significantly elevated, and the genes and proteins involved in phenolic acid biosynthesis and strigolactone biosynthesis were significantly altered, and some of the proteins (ASP1, 4CLL7, and CCD1) underwent acetylation modification. Meanwhile, correlation analysis showed that strigolactone was strongly correlated with differential phenolic acids, which might regulate the adaptive responses of the R. chrysanthum under UV-B stress. In this paper, we investigated the effects of strigolactone on the accumulation of phenolic acid compounds and found a strong correlation between strigolactone and elevated phenolic acid levels, which provided insights into the molecular mechanism of plant regulation of phenolic acid accumulation, and facilitated the adoption of measures to mitigate the adverse effects of UV-B stress on plant growth, and to achieve the purpose of protecting plant germplasm resources.

Emerging Functions of Protein Tyrosine Phosphatases in Plants

Reversible protein phosphorylation, known as the "switch" of the cell, is controlled by protein kinases (PKs) and protein phosphatases (PPs). Based on substrate specificity, PPs are classified into protein serine/threonine phosphatases and protein tyrosine phosphatases (PTPs). PTPs can dephosphorylate phosphotyrosine and phosphoserine/phosphothreonine. In plants, PTPs monitor plant physiology, growth, and development. This review summarizes an overview of the PTPs' classification and describes how PTPs regulate various plant processes, including plant growth and development, plant hormone responses, and responses to abiotic and biotic stresses. Then, future research directions on the PTP family in plants are discussed. This summary will serve as a reference for researchers studying PTPs in plants.

Metabolomic Analysis of Elymus sibiricus Exposed to UV-B Radiation Stress

Plants cultivated on the Qinghai-Tibet Plateau (QTP) are exposed to high ultraviolet radiation intensities, so they require effective mechanisms to adapt to these stress conditions. UV-B radiation is an abiotic stress factor that affects plant growth, development, and environmental adaptation. Elymus sibiricus is a common species in the alpine meadows of the QTP, with high-stress resistance, large biomass, and high nutritional value. This species plays an important role in establishing artificial grasslands and improving degraded grasslands. In this study, UV-B radiation-tolerant and UV-B radiation-sensitive E. sibiricus genotypes were subjected to simulated short-term (5 days, 10 days) and long-term (15 days, 20 days) UV-B radiation stress and the metabolite profiles evaluated to explore the mechanism underlying UV-B radiation resistance in E. sibiricus. A total of 699 metabolites were identified, including 11 primary metabolites such as lipids and lipid-like molecules, phenylpropanoids and polyketides, organic acids and their derivatives, and organic oxygen compounds. Principal component analysis distinctly clustered the samples according to the cultivar, indicating that the two genotypes exhibit distinct response mechanisms to UV-B radiation stress. The results showed that 14 metabolites, including linoleic acid, LPC 18:2, xanthosine, and 23 metabolites, including 2-one heptamethoxyflavone, glycyrrhizin, and caffeic acid were differentially expressed under short-term and long-term UV-B radiation stress, respectively. Therefore, these compounds are potential biomarkers for evaluating E. sibiricus response to UV-B radiation stress. Allantoin specific and consistent expression was up-regulated in the UV-B radiation-tolerant genotype, thereby it can be used to identify varieties resistant to UV-B radiation. Different metabolic profiles and UV-B radiation response mechanisms were observed between the UV-B radiation-tolerant and UV-B radiation-sensitive E. sibiricus genotypes. A model for the metabolic pathways and metabolic profiles was constructed for the two genotypes. This metabolomic study on the E. sibiricus response to UV-B radiation stress provides a reference for the breeding of new UV-B radiation-tolerant E. sibiricus cultivars.

A review on ubiquitin ligases: Orchestrators of plant resilience in adversity

Ubiquitin- proteasome system (UPS) is universally present in plants and animals, mediating many cellular processes needed for growth and development. Plants constantly defend themselves against endogenous and exogenous stimuli such as hormonal signaling, biotic stresses such as viruses, fungi, nematodes, and abiotic stresses like drought, heat, and salinity by developing complex regulatory mechanisms. Ubiquitination is a regulatory mechanism involving selective elimination and stabilization of regulatory proteins through the UPS system where E3 ligases play a central role; they can bind to the targets in a substrate-specific manner, followed by poly-ubiquitylation, and subsequent protein degradation by 26 S proteasome. Increasing evidence suggests different types of E3 ligases play important roles in plant development and stress adaptation. Herein, we summarize recent advances in understanding the regulatory roles of different E3 ligases and primarily focus on protein ubiquitination in plant-environment interactions. It also highlights the diversity and complexity of these metabolic pathways that enable plant to survive under challenging conditions. This reader-friendly review provides a comprehensive overview of E3 ligases and their substrates associated with abiotic and biotic stresses that could be utilized for future crop improvement.

Mechanism of Phloretin Accumulation in Malus hupehensis Grown at High Altitudes: Evidence from Quantitative 4D Proteomics

Phloretin is a natural dihydrochalcone (DHC) that exhibits various pharmacological and therapeutic activities. Malus hupehensis Rehd. (M. hupehensis) is widely planted in the middle of China and its leaves contain an extremely high content of phloridzin, a glycosylated derivative of phloretin. In the present study, we observed a significant increase in phloretin content in the leaves of M. hupehensis planted at high altitudes. To investigate the mechanisms of phloretin accumulation, we explored changes in the proteome profiles of M. hupehensis plants grown at various altitudes. The results showed that at high altitudes, photosynthesis- and DHC biosynthesis-related proteins were downregulated and upregulated, respectively, leading to reduced chlorophyll content and DHC accumulation in the leaves. Moreover, we identified a novel phloridzin-catalyzing glucosidase whose expression level was significantly increased in high-altitude-cultivated plants. This work provided a better understanding of the mechanism of phloretin accumulation and effective and economic strategies for phloretin production.

Variation in ultraviolet-B (UV-B)-induced DNA damage repair mechanisms in plants and humans: an avenue for developing protection against skin photoaging

PURPOSE

The increasing amounts of ultraviolet-B (UV-B) light in our surroundings have sparked worries about the possible effects on humans and plants. The detrimental effects of heightened UV-B exposure on these two vital elements of terrestrial life are different due to their unique and concurrent nature. Understanding common vulnerabilities and distinctive adaptations of UV-B radiation by exploring the physiological and biochemical responses of plants and the effects on human health is of huge importance. The comparative effects of UV-B radiation on plants and animals, however, are poorly studied. This review sheds light on the sophisticated web of UV-B radiation effects by navigating the complex interaction between botanical and medical perspectives, drawing upon current findings.

CONCLUSION

By providing a comprehensive understanding of the complex effects of heightened UV-B radiation on plants and humans, this study summarizes relevant adaptation strategies to the heightened UV-B radiation stress, which offer new approaches for improving human cellular resilience to environmental stressors.

Study of changes in folding/unfolding properties and stability of Arabidopsis thaliana MYB12 transcription factor following UV-B exposure in vitro

Flavonoids mostly protect plant cells from the harmful effects of UV-B radiation from the sun. In plants, the R2R3-subfamily of the MYB transcription factor, MYB12, is a key inducer of the biosynthesis of flavonoids. Our study involves the biophysical characterization of Arabidopsis thaliana MYB12 protein (AtMYB12) under UV-B exposure in vitro. Tryptophan fluorescence studies using recombinant full-length AtMYB12 (native) and the N-terminal truncated versions (first N-terminal MYB domain absent in AtMYB12Δ1, and both the first and second N-terminal MYB domains absent in AtMYB12Δ2) have revealed prominent alteration in the tryptophan microenvironment in AtMYB12Δ1 and AtMYB12Δ2 protein as a result of UV-B exposure as compared with the native AtMYB12. Bis-ANS binding assay and urea-mediated denaturation profiling showed an appreciable change in the structural conformation in AtMYB12Δ1 and AtMYB12Δ2 proteins as compared with the native AtMYB12 protein following UV-B irradiation. UV-B-treated AtMYB12Δ2 showed a higher predisposition of aggregate formation in vitro. CD spectral analyses revealed a decrease in α-helix percentage with a concomitant increase in random coiled structure formation in AtMYB12Δ1 and AtMYB12Δ2 as compared to native AtMYB12 following UV-B treatment. Overall, these findings highlight the critical function of the N-terminal MYB domains in maintaining the stability and structural conformation of the AtMYB12 protein under UV-B stress in vitro.

Golden 2-like Transcription Factors Regulate Photosynthesis under UV-B Stress by Regulating the Calvin Cycle

UV-B stress can affect plant growth at different levels, and although there is a multitude of evidence confirming the effects of UV-B radiation on plant photosynthesis, there are fewer studies using physiological assays in combination with multi-omics to investigate photosynthesis in alpine plants under stressful environments. Golden 2-like (G2-like/GLK) transcription factors (TFs) are highly conserved during evolution and may be associated with abiotic stress. In this paper, we used Handy-PEA and Imaging-PAM Maxi to detect chlorophyll fluorescence in leaves of Rhododendron chrysanthum Pall. (R. chrysanthum) after UV-B stress, and we also investigated the effect of abscisic acid (ABA) on photosynthesis in plants under stress environments. We used a combination of proteomics, widely targeted metabolomics, and transcriptomics to study the changes of photosynthesis-related substances after UV-B stress. The results showed that UV-B stress was able to impair the donor side of photosystem II (PSII), inhibit electron transfer and weaken photosynthesis, and abscisic acid was able to alleviate the damage caused by UV-B stress to the photosynthetic apparatus. Significant changes in G2-like transcription factors occurred in R. chrysanthum after UV-B stress, and differentially expressed genes localized in the Calvin cycle were strongly correlated with members of the G2-like TF family. Multi-omics assays and physiological measurements together revealed that G2-like TFs can influence photosynthesis in R. chrysanthum under UV-B stress by regulating the Calvin cycle. This paper provides insights into the study of photosynthesis in plants under stress, and is conducive to the adoption of measures to improve photosynthesis in plants under stress to increase yield.

UV light and adaptive divergence of leaf physiology, anatomy, and ultrastructure drive heat stress tolerance in genetically distant grapevines

The genetic basis of plant response to light and heat stresses had been unveiled, and different molecular mechanisms of leaf cell homeostasis to keep high physiological performances were recognized in grapevine varieties. However, the ability to develop heat stress tolerance strategies must be further elucidated since the morpho-anatomical and physiological traits involved may vary with genotype × environment combination, stress intensity, and duration. A 3-year experiment was conducted on potted plants of Sardinian red grapevine cultivars Cannonau (syn. Grenache) and Carignano (syn. Carignan), exposed to prolonged heat stress inside a UV-blocking greenhouse, either submitted to low daily UV-B doses of 4.63 kJ m-2 d-1 (+UV) or to 0 kJ m-2 d-1 (-UV), and compared to a control (C) exposed to solar radiation (4.05 kJ m-2 d-1 average UV-B dose). Irrigation was supplied to avoid water stress, and canopy light and thermal microclimate were monitored continuously. Heat stress exceeded one-third of the duration inside the greenhouse and 6% in C. In vivo spectroscopy, including leaf reflectance and fluorescence, allowed for characterizing different patterns of leaf traits and metabolites involved in oxidative stress protection. Cannonau showed lower stomatal conductance under C (200 mmol m-2 s-1) but more than twice the values inside the greenhouse (400 to 900 mmol m-2 s-1), where water use efficiency was reduced similarly in both varieties. Under severe heat stress and -UV, Cannonau showed a sharper decrease in primary photochemical activity and higher leaf pigment reflectance indexes and leaf mass area. UV-B increased the leaf pigments, especially in Carignano, and different leaf cell regulatory traits to prevent oxidative damage were observed in leaf cross-sections. Heat stress induced chloroplast swelling, plastoglobule diffusion, and the accumulation of secretion deposits in both varieties, aggravated in Cannonau -UV by cell vacuolation, membrane dilation, and diffused leaf blade spot swelling. Conversely, in Carignano UV-B, cell wall barriers and calcium oxalate crystals proliferated in mesophyll cells. These responses suggest an adaptive divergence among cultivars to prolonged heat stress and UV-B light. Further research on grapevine biodiversity, heat, and UV-B light interactions may give new insights on the extent of stress tolerance to improve viticulture adaptive strategies in climate change hotspots.

Effects of Different Doses of sUV-B Exposure on Taxane Compounds' Metabolism in Taxus wallichiana var. Mairei

UV-B is an important environmental factor that differentially affects plant growth and secondary metabolites. The effects of supplemental ultraviolet-B (sUV-B) exposure (T1, 1.40 kJ·m-2·day-1; T2, 2.81 kJ·m-2·day-1; and T3, 5.62 kJ·m-2·day-1) on the growth biomass, physiological characteristics, and secondary metabolites were studied. Our results indicated that leaf thickness was significantly (p < 0.05) reduced under T3 relative to the control (natural light exposure, CK); The contents of 6-BA and IAA were significantly reduced (p < 0.05); and the contents of ABA, 10-deacetylbaccatin III, and baccatin III were significantly (p < 0.05) increased under T1 and T2. The paclitaxel content was the highest (0.036 ± 0.0018 mg·g-1) under T3. The cephalomannine content was significantly increased under T1. Hmgr gene expression was upregulated under T1 and T3. The gene expressions of Bapt and Dbtnbt were significantly (p < 0.05) upregulated under sUV-B exposure, and the gene expressions of CoA, Ts, and Dbat were significantly (p < 0.05) downregulated. A correlation analysis showed that the 6-BA content had a significantly (p < 0.05) positive correlation with Dbat gene expression. The IAA content had a significantly (p < 0.05) positive correlation with the gene expression of Hmgr, CoA, Ts, and Dbtnbt. The ABA content had a significantly (p < 0.05) positive correlation with Bapt gene expression. Dbat gene expression had a significantly (p < 0.05) positive correlation with the 10-deacetylbaccatin content. Hmgr gene expression was positively correlated with the contents of baccatin III and cephalomannine. Bapt gene expression had a significantly (p < 0.01) positive correlation with the paclitaxel content. A factor analysis showed that the accumulation of paclitaxel content was promoted under T2, which was helpful in clarifying the accumulation of taxane compounds after sUV-B exposure.

MYB4, a member of R2R3-subfamily of MYB transcription factor functions as a repressor of key genes involved in flavonoid biosynthesis and repair of UV-B induced DNA double strand breaks in Arabidopsis

Plants accumulate flavonoids as part of UV-B acclimation, while a high level of UV-B irradiation induces DNA damage and leads to genome instability. Here, we show that MYB4, a member of the R2R3-subfamily of MYB transcription factor plays important role in regulating plant response to UV-B exposure through the direct repression of the key genes involved in flavonoids biosynthesis and repair of DNA double-strand breaks (DSBs). Our results demonstrate that MYB4 inhibits seed germination and seedling establishment in Arabidopsis following UV-B exposure. Phenotype analyses of atmyb4-1 single mutant line along with uvr8-6/atmyb4-1, cop1-6/atmyb4-1, and hy5-215/atmyb4-1 double mutants indicate that MYB4 functions downstream of UVR8 mediated signaling pathway and negatively affects UV-B acclimation and cotyledon expansion. Our results indicate that MYB4 acts as transcriptional repressor of two key flavonoid biosynthesis genes, including 4CL and FLS, via directly binding to their promoter, thus reducing flavonoid accumulation. On the other hand, AtMYB4 overexpression leads to higher accumulation level of DSBs along with repressed expression of several key DSB repair genes, including AtATM, AtKU70, AtLIG4, AtXRCC4, AtBRCA1, AtSOG1, AtRAD51, and AtRAD54, respectively. Our results further suggest that MYB4 protein represses the expression of two crucial DSB repair genes, AtKU70 and AtXRCC4 through direct binding with their promoters. Together, our results indicate that MYB4 functions as an important coordinator to regulate plant response to UV-B through transcriptional regulation of key genes involved in flavonoids biosynthesis and repair of UV-B induced DNA damage.

Exogenous Cytokinin 4PU-30 Modulates the Response of Wheat and Einkorn Seedlings to Ultraviolet B Radiation

Abiotic stress is responsible for a significant reduction in crop plant productivity worldwide. Ultraviolet (UV) radiation is a natural component of sunlight and a permanent environmental stimulus. This study investigated the distinct responses of young wheat and einkorn plants to excessive UV-B radiation (180 min at λmax 312 nm) following foliar pretreatment with 1 µM synthetic cytokinin 4PU-30. Results demonstrated that UV radiation significantly amplified hydrogen peroxide levels in both wheat and einkorn, with einkorn exhibiting a more pronounced increase compared to wheat. This elevation indicated the induction of oxidative stress by UV radiation in the two genotypes. Intensified antioxidant enzyme activities and the increased accumulation of typical stress markers and non-enzyme protectants were evidenced. Transcriptional activity of genes encoding the key antioxidant enzymes POX, GST, CAT, and SOD was also investigated to shed some light on their genetic regulation in both wheat and einkorn seedlings. Our results suggested a role for POX1 and POX7 genes in the UV-B tolerance of the two wheat species as well as a cytokinin-stimulated UV-B stress response in einkorn involving the upregulation of the tau subfamily gene GSTU6. Based on all our findings, it could be concluded that 4PU-30 had the potential of alleviating oxidative stress by attenuating the symptoms of superfluous UV-B illumination in the two examined plant species.

Pivotal role of heterotrimeric G protein in the crosstalk between sugar signaling and abiotic stress response in plants

Heterotrimeric G-proteins are key modulators of multiple signaling and developmental pathways in plants, in which they act as molecular switches to engage in transmitting various stimuli signals from outside into the cells. Substantial studies have identified G proteins as essential components of the organismal response to abiotic stress, leading to adaptation and survival in plants. Meanwhile, sugars are also well acknowledged key players in stress perception, signaling, and gene expression regulation. Connections between the two significant signaling pathways in stress response are of interest to a general audience in plant biology. In this article, advances unraveling a pivotal role of G proteins in the process of sugar signals outside the cells being translated into the operation of autophagy in cells during stress are reviewed. In addition, we have presented recent findings on G proteins regulating the response to drought, salt, alkali, cold, heat and other abiotic stresses. Perspectives on G-protein research are also provided in the end. Since G protein signaling regulates many agronomic traits, elucidation of detailed mechanism of the related pathways would provide useful insights for the breeding of abiotic stress resistant and high-yield crops.

Phosphorylation of Arabidopsis UVR8 photoreceptor modulates protein interactions and responses to UV-B radiation

Exposure of plants to ultraviolet-B (UV-B) radiation initiates transcriptional responses that modify metabolism, physiology and development to enhance viability in sunlight. Many of these regulatory responses to UV-B radiation are mediated by the photoreceptor UV RESISTANCE LOCUS 8 (UVR8). Following photoreception, UVR8 interacts directly with multiple proteins to regulate gene expression, but the mechanisms that control differential protein binding to initiate distinct responses are unknown. Here we show that UVR8 is phosphorylated at several sites and that UV-B stimulates phosphorylation at Serine 402. Site-directed mutagenesis to mimic Serine 402 phosphorylation promotes binding of UVR8 to REPRESSOR OF UV-B PHOTOMORPHOGENESIS (RUP) proteins, which negatively regulate UVR8 action. Complementation of the uvr8 mutant with phosphonull or phosphomimetic variants suggests that phosphorylation of Serine 402 modifies UVR8 activity and promotes flavonoid biosynthesis, a key UV-B-stimulated response that enhances plant protection and crop nutritional quality. This research provides a basis to understand how UVR8 interacts differentially with effector proteins to regulate plant responses to UV-B radiation.

Abscisic Acid Affects Phenolic Acid Content to Increase Tolerance to UV-B Stress in Rhododendron chrysanthum Pall

The presence of the ozone hole increases the amount of UV radiation reaching a plant's surface, and UV-B radiation is an abiotic stress capable of affecting plant growth. Rhododendron chrysanthum Pall. (R. chrysanthum) grows in alpine regions, where strong UV-B radiation is present, and has been able to adapt to strong UV-B radiation over a long period of evolution. We investigated the response of R. chrysanthum leaves to UV-B radiation using widely targeted metabolomics and transcriptomics. Although phytohormones have been studied for many years in plant growth and development and adaptation to environmental stresses, this paper is innovative in terms of the species studied and the methods used. Using unique species and the latest research methods, this paper was able to add information to this topic for the species R. chrysanthum. We treated R. chrysanthum grown in a simulated alpine environment, with group M receiving no UV-B radiation and groups N and Q (externally applied abscisic acid treatment) receiving UV-B radiation for 2 days (8 h per day). The results of the MN group showed significant changes in phenolic acid accumulation and differential expression of genes related to phenolic acid synthesis in leaves of R. chrysanthum after UV-B radiation. We combined transcriptomics and metabolomics data to map the metabolic regulatory network of phenolic acids under UV-B stress in order to investigate the response of such secondary metabolites to stress. L-phenylalanine, L-tyrosine and phenylpyruvic acid contents in R. chrysanthum were significantly increased after UV-B radiation. Simultaneously, the levels of 3-hydroxyphenylacetic acid, 2-phenylethanol, anthranilate, 2-hydroxycinnamic acid, 3-hydroxycinnamic acid, α-hydroxycinnamic acid and 2-hydroxy-3-phenylpropanoic acid in this pathway were elevated in response to UV-B stress. In contrast, the study in the NQ group found that externally applied abscisic acid (ABA) in R. chrysanthum had greater tolerance to UV-B radiation, and phenolic acid accumulation under the influence of ABA also showed greater differences. The contents of 2-phenylethanol, 1-o-p-coumaroyl-β-d-glucose, 2-hydroxy-3-phenylpropanoic acid, 3-(4-hydroxyphenyl)-propionic acid and 3-o-feruloylquinic ac-id-o-glucoside were significantly elevated in R. chrysanthum after external application of ABA to protect against UV-B stress. Taken together, these studies of the three groups indicated that ABA can influence phenolic acid production to promote the response of R. chrysanthum to UV-B stress, which provided a theoretical reference for the study of its complex molecular regulatory mechanism.

Aerobic methane production by phytoplankton as an important methane source of aquatic ecosystems: Reconsidering the global methane budget

Biological methane, a major source of global methane budget, is traditionally thought to be produced in anaerobic environments. However, the recent reports about methane supersaturation occurring in oxygenated water layer, termed as "methane paradox", have challenged this prevailing paradigm. Significantly, growing evidence has indicated that phytoplankton including prokaryotic cyanobacteria and eukaryotic algae are capable of generating methane under aerobic conditions. In this regard, a systematic review of aerobic methane production by phytoplankton is expected to arouse the public attention, contributing to the understanding of methane paradox. Here, we comprehensively summarize the widespread phenomena of methane supersaturation in oxic layers. The remarkable correlation relationships between methane concentration and several key indicators (depth, chlorophyll a level and organic sulfide concentration) indicate the significance of phytoplankton in in-situ methane accumulation. Subsequently, four mechanisms of aerobic methane production by phytoplankton are illustrated in detail, including photosynthesis-driven metabolism, reactive oxygen species (ROS)-driven demethylation of methyl donors, methanogenesis catalyzed by nitrogenase and demethylation of phosphonates catalyzed by CP lyase. The first two pathways occur in various phytoplankton, while the latter two have been specially discovered in cyanobacteria. Additionally, the effects of four crucial factors on aerobic methane production by phytoplankton are also discussed, including phytoplankton species, light, temperature and crucial nutrients. Finally, the measures to control global methane emissions from phytoplankton, the precise intracellular mechanisms of methane production and a more complete global methane budget model are definitely required in the future research on methane production by phytoplankton. This review would provide guidance for future studies of aerobic methane production by phytoplankton and emphasize the potential contribution of aquatic ecosystems to global methane budget.

Physiological and omics-based insights for underpinning the molecular regulation of secondary metabolite production in medicinal plants: UV stress resilience

Despite complex phytoconstituents, the commercial potential of medicinal plants under ultraviolet (UV) stress environment hasn't been fully comprehended. Due to sessile nature, these plants are constantly exposed to damaging radiation, which disturbs their natural physiological and biochemical processes. To combat with UV stress, plants synthesized several small organic molecules (natural products of low molecular mass like alkaloids, terpenoids, flavonoids and phenolics, etc.) known as plant secondary metabolites (PSMs) that come into play to counteract the adverse effect of stress. Plants adapted a stress response by organizing the expression of several genes, enzymes, transcription factors, and proteins involved in the synthesis of chemical substances and by making the signaling cascade (a series of chemical reactions induced by a stimulus within a biological cell) flexible to boost the defensive response. To neutralize UV exposure, secondary metabolites and their signaling network regulate cellular processes at the molecular level. Conventional breeding methods are time-consuming and difficult to reveal the molecular pattern of the stress tolerance medicinal plants. Acquiring in-depth knowledge of the molecular drivers behind the defensive mechanism of medicinal plants against UV radiation would yield advantages (economical and biological) that will bring prosperity to the burgeoning world's population. Thus, this review article emphasized the comprehensive information and clues to identify several potential genes, transcription factors (TFs), proteins, biosynthetic pathways, and biological networks which are involved in resilience mechanism under UV stress in medicinal plants of high-altitudes.

α-Tocopherol application as a countermeasure to UV-B stress in bread wheat (Triticum aestivum L.)

The source of energy for all photoautotrophic organisms is light, which is absorbed by photosynthetic processes and used to transform carbon dioxide and H2O into organic molecules. The majority of UV-B light (280 to 320 nm) is absorbed by stratospheric ozone layer, although some of it does reach at the Earth's surface. Because of the sedentary lifestyle of plants, this form of abiotic stress is unavoidable and can induce growth and even cell death. Ten-day-old calli generated from mature Kirik wheat embryos were subjected to UV-B radiation for 0, 2, 4, and 6 h to examine the function of exogenous α-tocopherol, a lipophilic antioxidant, in wheat tolerance to UV-B radiation stress. The calli were then moved to a callus medium containing α-tocopherol (0, 50, and 100 mg/l) and cultivated there for 20 days after being subjected to UV-B stress. For plant regeneration, embryogenic calli were put on a medium for plant regeneration after 30 days. The findings of this investigation demonstrated that an increase in UV-B exposure period resulted in a substantial drop in the relative growth rate of callus, the rate of embryogenic callus, the rate of responding embryogenic callus, and the number of plants in each explant. On the other hand, with the application of α-tocopherol, all these parameters improved, and the best result was observed in the application of 100 mg/l of α-tocopherol in terms of plant regeneration under UV-B stress.

The Role of Reactive Oxygen Species in Plant Response to Radiation

Radiation is widespread in nature, including ultraviolet radiation from the sun, cosmic radiation and radiation emitted by natural radionuclides. Over the years, the increasing industrialization of human beings has brought about more radiation, such as enhanced UV-B radiation due to ground ozone decay, and the emission and contamination of nuclear waste due to the increasing nuclear power plants and radioactive material industry. With additional radiation reaching plants, both negative effects including damage to cell membranes, reduction of photosynthetic rate and premature aging and benefits such as growth promotion and stress resistance enhancement have been observed. ROS (Reactive oxygen species) are reactive oxidants in plant cells, including hydrogen peroxide (H2O2), superoxide anions (O2•-) and hydroxide anion radicals (·OH), which may stimulate the antioxidant system of plants and act as signaling molecules to regulate downstream reactions. A number of studies have observed the change of ROS in plant cells under radiation, and new technology such as RNA-seq has molecularly revealed the regulation of radiative biological effects by ROS. This review summarized recent progress on the role of ROS in plant response to radiations including UV, ion beam and plasma, and may help to reveal the mechanisms of plant responses to radiation.