Tomato UV-B receptor SlUVR8 mediates plant acclimation to UV-B radiation and enhances fruit chloroplast development via regulating SlGLK2

The recent possible strategies for breeding ultraviolet-B-resistant crops

The sensitivity of crops to ultraviolet B (UVB, 280-315 nm) radiation varies significantly. Plants' sensitivity to UVB is heavily influenced by the activity of the enzyme cyclobutane pyrimidine dimer (CPD) photolyase, which fixes UVB-induced CPDs. Crops grown in tropical areas with high level of UVB radiation, like O. glaberrima from Africa and O. sativa ssp. indica rice from Bengal, are more sensitive to UVB radiation and could suffer more as a result of rising UVB levels on the earth's surface. Therefore, creating crops that can withstand high UVB is crucial in tropical regions. There is, however, little information on current techniques for breeding UVB-resistant plants. The most recent techniques for producing UVB-resistant crops are presented in this review. The use of DNA methylation, boosting the antioxidant system, regulating the expression of micro-RNA396, and overexpressing CPD photolyase in transgenic plants are some of the methods that are discussed. CPD photolyase overexpression in transgenic plants is the most popular technique for producing UVB-resistant rice. The study also offers several strategies for creating UVB-resistant plants using gene editing techniques. To feed the world's rapidly expanding population, researchers can use the information from this study to improve food production.

METACASPASE8 (MC8) Is a Crucial Protein in the LSD1-Dependent Cell Death Pathway in Response to Ultraviolet Stress

LESION-SIMULATING DISEASE1 (LSD1) is one of the well-known cell death regulatory proteins in Arabidopsis thaliana. The lsd1 mutant exhibits runaway cell death (RCD) in response to various biotic and abiotic stresses. The phenotype of the lsd1 mutant strongly depends on two other proteins, ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) and PHYTOALEXIN-DEFICIENT 4 (PAD4) as well as on the synthesis/metabolism/signaling of salicylic acid (SA) and reactive oxygen species (ROS). However, the most interesting aspect of the lsd1 mutant is its conditional-dependent RCD phenotype, and thus, the defined role and function of LSD1 in the suppression of EDS1 and PAD4 in controlled laboratory conditions is different in comparison to a multivariable field environment. Analysis of the lsd1 mutant transcriptome in ambient laboratory and field conditions indicated that there were some candidate genes and proteins that might be involved in the regulation of the lsd1 conditional-dependent RCD phenotype. One of them is METACASPASE 8 (AT1G16420). This type II metacaspase was described as a cell death-positive regulator induced by UV-C irradiation and ROS accumulation. In the double mc8/lsd1 mutant, we discovered reversion of the lsd1 RCD phenotype in response to UV radiation applied in controlled laboratory conditions. This cell death deregulation observed in the lsd1 mutant was reverted like in double mutants of lsd1/eds1 and lsd1/pad4. To summarize, in this work, we demonstrated that MC8 is positively involved in EDS1 and PAD4 conditional-dependent regulation of cell death when LSD1 function is suppressed in Arabidopsis thaliana. Thus, we identified a new protein compound of the conditional LSD1-EDS1-PAD4 regulatory hub. We proposed a working model of MC8 involvement in the regulation of cell death and we postulated that MC8 is a crucial protein in this regulatory pathway.

Enhanced ultraviolet-B radiation alleviates structural damages on rice leaf caused by Magnaporthe oryzae infection

Enhanced ultraviolet-B (UV-B) radiation can change the interaction between crops and pathogens. The effects of single and compound stresses of enhanced UV-B radiation (5.0 kJ·m-2) and Magnaporthe oryzae on the morphology, anatomy, and ultrastructure of rice leaves were investigated. M. oryzae infection decreased the leaf area and thickness, reduced the stomatal area and density, and caused damages to the leaf ultrastructure, such as cytoplasm-cell wall separation, atrophy and sinking of fan-shaped bulliform cells, and chloroplast deformation. The enhanced UV-B radiation supplied before or during M. oryzae infection remarkably decreased the mycelia number of M. oryzae in leaf epidermis, increased the leaf area, leaf thickness, stomatal density, and mastoid number; and alleviated the ultrastructural damages induced by M. oryzae to keep an integral chloroplast. While the UV-B radiation was supplied after M. oryzae infection, its alleviation effects on the damages induced by M. oryzae infection on the morphology and structure of rice leaf were attenuated. Thus, the alleviation of enhanced UV-B radiation on damages induced by M. oryzae infection on rice leaves was related to its application period. The enhanced UV-B radiation supplied before or during M. oryzae infection allowed the rice leaf to resist M. oryzae infection.

The flavour of grape colour: anthocyanin content tunes aroma precursor composition by altering the berry microenvironment

Anthocyaninless (white) instead of black/red (coloured) fruits develop in grapevine cultivars without functional VviMYBA1 and VviMYBA2 genes, and this conditions the colour of wines that can be produced. To evaluate whether this genetic variation has additional consequences on fruit ripening and composition, we performed comparisons of microenvironment, transcriptomics, and metabolomics of developing grapes between near-isogenic white- and black-berried somatic variants of Garnacha and Tempranillo cultivars. Berry temperature was as much as 3.5 ºC lower in white- compared to black-berried Tempranillo. An RNA-seq study combined with targeted and untargeted metabolomics revealed that ripening fruits of white-berried variants were characterized by the up-regulation of photosynthesis-related and other light-responsive genes and by their higher accumulation of specific terpene aroma precursors, fatty acid-derived aldehyde volatiles, and phenylpropanoid precursor amino acids. MYBA1-MYBA2 function proved essential for flavonol trihydroxylation in black-berried somatic variants, which were also characterized by enhanced expression of pathogen defence genes in the berry skin and increased accumulation of C6-derived alcohol and ester volatiles and γ-aminobutyric acid. Collectively, our results indicate that anthocyanin depletion has side-effects on grape composition by altering the internal microenvironment of the berry and the partitioning of the phenylpropanoid pathway. Our findings show how fruit colour can condition other fruit features, such as flavour potential and stress homeostasis.

OsCM regulates rice defence system in response to UV light supplemented with drought stress

Studies on plant responses to combined abiotic stresses are very limited, especially in major crop plants. The current study evaluated the response of chorismate mutase overexpressor (OxCM) rice line to combined UV light and drought stress. The experiments were conducted in pots in a growth chamber, and data were assessed for gene expression, antioxidant and hormone regulation, flavonoid accumulation, phenotypic variation, and amino acid accumulation. Wild-type (WT) rice had reduced the growth and vigour, while transgenic rice maintained growth and vigour under combined UV light and drought stress. ROS and lipid peroxidation analysis revealed that chorismate mutase (OsCM) reduced oxidative stress mediated by ROS scavenging and reduced lipid peroxidation. The combined stresses reduced biosynthesis of total flavonoids, kaempferol and quercetin in WT plants, but increased significantly in plants with OxCM. Phytohormone analysis showed that SA was reduced by 50% in WT and 73% in transgenic plants, while ABA was reduced by 22% in WT plants but increased to 129% in transgenic plants. Expression of chorismate mutase regulates phenylalanine biosynthesis, UV light and drought stress-responsive genes, e.g., phenylalanine ammonia lyase (OsPAL), dehydrin (OsDHN), dehydration-responsive element-binding (OsDREB), ras-related protein 7 (OsRab7), ultraviolet-B resistance 8 (OsUVR8), WRKY transcription factor 89 (OsWRKY89) and tryptophan synthase alpha chain (OsTSA). Moreover, OsCM also increases accumulation of free amino acids (aspartic acid, glutamic acid, leucine, tyrosine, phenylalanine and proline) and sodium (Na), potassium (K), and calcium (Ca) ions in response to the combined stresses. Together, these results suggest that chorismate mutase expression induces physiological, biochemical and molecular changes that enhance rice tolerance to combined UV light and drought stresses.

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

Ultraviolet-B (UV-B) light is an intrinsic part of sunlight that reaches the earth's surface, and affects plant survival and adaptation. How plants respond to UV-B light is regulated by the wavelength, intensity and duration of UV-B radiation, and is also regulated by photosynthetically active radiation perceived by phytochrome and cryptochrome photoreceptors. Non-damaging UV-B light promotes plant photomorphogenesis and UV-B acclimation which enhances plant tolerance against UV-B stress. However, high-level UV-B radiation induces DNA damage, generates reactive oxygen species (ROS) and impairs photosynthesis. Plants have evolved efficient mechanisms to utilize informational UV-B signal, and protect themselves from UV-B stress. UV RESISTANCE LOCUS8 (UVR8) is a conserved plant-specific UV-B photoreceptor. It interacts with CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1) to initiate UV-B-specific light signaling and regulate UV-B responsive gene expression. A set of transcription factors such as ELONGATED HYPOCOTYL5 (HY5) function downstream of the UVR8-COP1 module to promote seedling de-etiolation for photomorphogenic development and biosynthesis of sunscreen flavonoids for UV-B stress tolerance. In addition to UVR8 signaling pathways, plants subjected to damaging UV-B radiation initiate stress protection and repair mechanisms through UVR8-independent pathways. In this review, we summarize the emerging mechanisms underlying UV-B stress acclimation and protection in plants, primarily revealed in the model plant Arabidopsis thaliana.

Chromosomal fragment deletion in APRR2-repeated locus modulates the dark stem color in Cucurbita pepo

Cp4.1LG15g03420 (CpDsc-1), which encodes a two-component response regulator-like protein (APRR2) in the nucleus, influences dark green stem formation in Cucurbita pepo by regulating the chlorophyll content. Stem color is an important agronomic trait in zucchini (Cucurbita pepo) for robust seeding and high yield. However, the gene controlling the stem color has not been characterized. In this study, we identified a single locus accounting for the dark green stem color of C. pepo (CpDsc-1). Genetic analysis of this trait in segregated populations derived from two parental lines (line 296 with dark green stems and line 274 with light green stems) revealed that stem color was controlled by a single dominant gene (dark green vs. light green). In bulked segregant analysis, CpDsc-1 was mapped to a 2.09-Mb interval on chromosome 15. This region was further narrowed to 65.2 kb using linkage analysis of the F₂ population. Sequencing analysis revealed a 14 kb deletion between Cp4.1LG15g03420 and Cp4.1LG15g03360; these two genes both encoded a two-component response regulator-like protein (APRR2). The incomplete structures of the two APRR2 genes and abnormal chloroplasts in line 274 might be the main cause of the light green phenotype. Gene expression pattern analysis showed that only Cp4.1LG15g03420 was upregulated in line 296. Subcellular localization analysis indicated that Cp4.1LG15g03420 was a nuclear gene. Furthermore, a co-dominant marker, G4563 (93% accuracy rate), and a co-segregation marker, Fra3, were established in 111 diverse germplasms; both of these markers were tightly linked with the color trait. This study provided insights into chlorophyll regulation mechanisms and revealed the markers valuable for marker-assisted selection in future zucchini breeding.

Identification and characterization of tsyl1, a thermosensitive chlorophyll-deficient mutant in rice (Oryza sativa)

Chloroplast development and chlorophyll biosynthesis are affected by temperature. However, the underlying molecular mechanism of this phenomenon remains elusive. Here, we isolated and characterized a thermosensitive yellow-green leaf mutant named tsyl1 (thermosensitive yellow leaf 1) from an ethylmethylsulfone (EMS)-mutagenized pool of rice. The mutant exhibits a yellow-green leaf phenotype and decreased leaf chlorophyll contents throughout development. At the mature stage of the tsyl1 mutant, the plant height, tiller number, number of spikelets per panicle and 1000 seed weight were decreased significantly compared to those of wild-type plants, but the seed setting rate and panicle length were not. The mutant phenotype was controlled by a single recessive nuclear gene on the short arm of rice chromosome 11. Map-based cloning of TSYL1, followed by a complementation experiment, showed a G base deletion at the coding region of LOC_Os11g05552, leading to the yellow-green phenotype. The TSYL1 gene encodes a signal recognition particle 54 kDa (SRP54) protein that is conserved in all organisms. The expression of tsyl1 was induced by high temperature. Furthermore, the expression of chlorophyll biosynthesis- and chloroplast development-related genes was influenced in tsyl1 at different temperatures. These results indicated that the TSYL1 gene plays a key role in chlorophyll biosynthesis and is affected by temperature at the transcriptional level.

Tea GOLDEN2-LIKE genes enhance catechin biosynthesis through activating R2R3-MYB transcription factor

The biosynthesis of catechins, a major type of flavonoids accumulated in tea, is mediated by developmental cues and environmental stimuli. Light enhances but shading treatment reduces catechin accumulation in tea leaves. However, the transcription factors involved in light-mediated catechin biosynthesis remain to be identified. Two GOLDEN2 LIKE genes from tea plant (CsGLK1 and CsGLK2) were isolated and characterized in both tomato and tea plants. Transcripts of both CsGLK1 and CsGLK2 were affected by light intensity in tea plants. Overexpression of CsGLK1 and CsGLK2 promoted chloroplast development and carotenoid accumulation in tomato fruits. An integrated metabolomic and transcriptomic approach revealed that both catechin content and related biosynthetic genes were upregulated in CsGLK-overexpressing tomato leaves. Our further studies in tea plants indicated that CsGLKs directly regulate the transcription of CsMYB5b, a transcription factor involved in catechin biosynthesis. Suppression of CsGLKs in tea leaves led to the reduction of both CsMYB5b expression and catechin accumulation. Taken together, the results show that CsGLKs are involved in light-regulated catechin accumulation in tea plants by regulating expression of CsMYB5b and have great potential for enhancing the accumulation of both carotenoids and flavonoids in fruits of horticultural crops.

Drought and UV Radiation Stress Tolerance in Rice Is Improved by Overaccumulation of Non-Enzymatic Antioxidant Flavonoids

Drought and ultraviolet radiation (UV radiation) are the coexisting environmental factors that negatively affect plant growth and development via oxidative damage. Flavonoids are reactive, scavenging oxygen species (ROS) and UV radiation-absorbing compounds generated under stress conditions. We investigated the biosynthesis of kaempferol and quercetin in wild and flavanone 3-hydroxylase (F3H) overexpresser rice plants when drought and UV radiation stress were imposed individually and together. Phenotypic variation indicated that both kinds of stress highly reduced rice plant growth parameters in wild plants as compared to transgenic plants. When combined, the stressors adversely affected rice plant growth parameters more than when they were imposed individually. Overaccumulation of kaempferol and quercetin in transgenic plants demonstrated that both flavonoids were crucial for enhanced tolerance to such stresses. Oxidative activity assays showed that kaempferol and quercetin overaccumulation with strong non-enzymatic antioxidant activity mitigated the accumulation of ROS under drought and UV radiation stress. Lower contents of salicylic acid (SA) in transgenic plants indicated that flavonoid accumulation reduced stress, which led to the accumulation of low levels of SA. Transcriptional regulation of the dehydrin (DHN) and ultraviolet-B resistance 8 (UVR8) genes showed significant increases in transgenic plants compared to wild plants under stress. Taken together, these results confirm the usefulness of kaempferol and quercetin in enhancing tolerance to both drought and UV radiation stress.

Flavonoid deficiency disrupts redox homeostasis and terpenoid biosynthesis in glandular trichomes of tomato

Glandular trichomes (GTs) are epidermal structures that provide the first line of chemical defense against arthropod herbivores and other biotic threats. The most conspicuous structure on leaves of cultivated tomato (Solanum lycopersicum) is the type-VI GT (tVI-GT), which accumulates both flavonoids and volatile terpenoids. Although these classes of specialized metabolites are derived from distinct metabolic pathways, previous studies with a chalcone isomerase 1 (CHI1)-deficient mutant called anthocyanin free (af) showed that flavonoids are required for terpenoid accumulation in tVI-GTs. Here, we combined global transcriptomic and proteomic analyses of isolated trichomes as a starting point to show that the lack of CHI1 is associated with reduced levels of terpenoid biosynthetic transcripts and enzymes. The flavonoid deficiency in af trichomes also resulted in the upregulation of abiotic stress-responsive genes associated with DNA damage and repair. Several lines of biochemical and genetic evidence indicate that the terpenoid defect in af mutants is specific for the tVI-GT and is associated with the absence of bulk flavonoids rather than loss of CHI1 per se. A newly developed genome-scale model of metabolism in tomato tVI-GTs helped identify metabolic imbalances caused by the loss of flavonoid production. We provide evidence that flavonoid deficiency in this cell type leads to increased production of reactive oxygen species (ROS), which may impair terpenoid biosynthesis. Collectively, our findings support a role for flavonoids as ROS-scavenging antioxidants in GTs.

Perception and Signaling of Ultraviolet-B Radiation in Plants

Ultraviolet-B (UV-B) radiation is an intrinsic fraction of sunlight that plants perceive through the UVR8 photoreceptor. UVR8 is a homodimer in its ground state that monomerizes upon UV-B photon absorption via distinct tryptophan residues. Monomeric UVR8 competitively binds to the substrate binding site of COP1, thus inhibiting its E3 ubiquitin ligase activity against target proteins, which include transcriptional regulators such as HY5. The UVR8-COP1 interaction also leads to the destabilization of PIF bHLH factor family members. Additionally, UVR8 directly interacts with and inhibits the DNA binding of a different set of transcription factors. Each of these UVR8 signaling mechanisms initiates nuclear gene expression changes leading to UV-B-induced photomorphogenesis and acclimation. The two WD40-repeat proteins RUP1 and RUP2 provide negative feedback regulation and inactivate UVR8 by facilitating redimerization. Here, we review the molecular mechanisms of the UVR8 pathway from UV-B perception and signal transduction to gene expression changes and physiological UV-B responses.

Selection and optimization of reference genes for RT-qPCR normalization: A case study in Solanum lycopersicum exposed to UV-B

Quantitative RT- PCR is one of the most common methods to study gene expression in response to stress. Therefore, it is crucial to have suitable reference genes (RGs) for result normalization. Although several reports describe UV-B-modulated gene expression in Solanum lycopersicum, there are no suitable RGs identified until now. The aim of this work was to evaluate the suitability of seven traditional genes: actin (ACT), tubulin (TUB), ubiquitin (UBI), glyceraldehyde- 3 phosphate dehydrogenase (GAPDH), elongation factor 1α (EF1α), phosphatase 2A catalytic subunit (PP2A) and GAGA binding transcriptional activator (GAGA); and two non-traditional genes: thioredoxin h1 (TRX h1) and UV-B RESISTANCE LOCUS 8 (UVR8), as candidate RGs for their potential use as reliable internal controls in leaves, stems and roots of tomato seedlings exposed to acute and chronic UV-B. The stability of these genes expression was evaluated using five statistical algorithms: geNorm, NormFinder, BestKeeper, Delta Ct and ANOVA. Considering the comprehensive stability ranking, we recommend ACT+TUB as the best pair of RGs for leaves, PP2A+GAPDH+TRX h1 for stems and TUB+UVR8 for roots. The reliability of the selected RGs for each tissue was verified amplifying tomato chalcone synthase 1 (CHS1) and cyclobutane pyrimidine dimer (CPD) photolyase (PHR1-LIKE). Under UV-B treatment, CHS1 was upregulated in leaves, stems and roots whereas PHR1-LIKE was only upregulated in leaves and stems. This interpretation differs when the most and least stable RGs are chosen. This is the first report regarding suitable RGs selection for accurate normalization of gene expression in tomato seedlings exposed to UV-B irradiation.

A constitutively monomeric UVR8 photoreceptor confers enhanced UV-B photomorphogenesis

Coping with UV-B is crucial for plant survival in sunlight. The UV-B photoreceptor UVR8 regulates gene expression associated with photomorphogenesis, acclimation, and UV-B stress tolerance. UV-B photon reception by UVR8 homodimers results in monomerization, followed by interaction with the key signaling protein COP1. We have discovered a UV-B hypersensitive UVR8 photoreceptor that confers strongly enhanced UV-B tolerance and generated a UVR8 variant based on the underlying mutation that shows extremely enhanced constitutive signaling activity. Our findings provide key mechanistic insight into how plants respond and acclimate to UV-B radiation.

The plant ultraviolet-B (UV-B) photoreceptor UVR8 plays an important role in UV-B acclimation and survival. UV-B absorption by homodimeric UVR8 induces its monomerization and interaction with the E3 ubiquitin ligase COP1, leading ultimately to gene expression changes. UVR8 is inactivated through redimerization, facilitated by RUP1 and RUP2. Here, we describe a semidominant, hyperactive allele, namely uvr8-17D, that harbors a glycine-101 to serine mutation. UVR8^G101S overexpression led to weak constitutive photomorphogenesis and extreme UV-B responsiveness. UVR8^G101S was observed to be predominantly monomeric in vivo and, once activated by UV-B, was not efficiently inactivated. Analysis of a UVR8 crystal structure containing the G101S mutation revealed the distortion of a loop region normally involved in stabilization of the UVR8 homodimer. Plants expressing a UVR8 variant combining G101S with the previously described W285A mutation exhibited robust constitutive photomorphogenesis. This work provides further insight into UVR8 activation and inactivation mechanisms and describes a genetic tool for the manipulation of photomorphogenic responses.

The Photomorphogenic Transcription Factor PpHY5 Regulates Anthocyanin Accumulation in Response to UVA and UVB Irradiation

Red coloration contributes to fruit quality and is determined by anthocyanin content in peach (Prunus persica). Our previous study illustrated that anthocyanin accumulation is strongly regulated by light, and the effect of induction differs according to light quality. Here we showed that both ultraviolet-A (UVA) and ultraviolet-B (UVB) irradiation promoted anthocyanin biosynthesis in "Hujingmilu" peach fruit, and a combination of UVA and UVB had additional effects. The expression of anthocyanin biosynthesis and light signaling related genes, including transcription factor genes and light signaling elements, were induced following UV irradiation as early as 6 h post-treatment, earlier than apparent change in coloration which occurred at 72 h. To investigate the molecular mechanisms for UVA- and UVB-induced anthocyanin accumulation, the genes encoding ELONGATED HYPOCOTYL 5 (HY5), CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1), Cryptochrome (CRY), and UV RESISTANCE LOCUS 8 (UVR8) in peach were isolated and characterized through functional complementation in corresponding Arabidopsis (Arabidopsis thaliana) mutants. PpHY5 and PpCOP1.1 restored hypocotyl length and anthocyanin content in Arabidopsis mutants under white light; while PpCRY1 and PpUVR8.1 restored AtHY5 expression in Arabidopsis mutants in response to UV irradiation. Arabidopsis PpHY5/hy5 transgenic lines accumulated higher amounts of anthocyanin under UV supplementation (compared with weak white light only), especially when UVA and UVB were applied together. These data indicated that PpHY5, acting as AtHY5 counterpart, was a vital regulator in UVA and UVB signaling pathway. In peach, the expression of PpHY5 was up-regulated by UVA and UVB, and PpHY5 positively regulated both its own transcription by interacting with an E-box in its own promoter, and the transcription of the downstream anthocyanin biosynthetic genes chalcone synthase 1 (PpCHS1), chalcone synthase 2 (PpCHS2), and dihydroflavonol 4-reductase (PpDFR1) as well as the transcription factor gene PpMYB10.1. In summary, functional evidence supports the role of PpHY5 in UVA and UVB light transduction pathway controlling anthocyanin biosynthesis. In peach this is via up-regulation of expression of genes encoding biosynthetic enzymes, as well as the transcription factor PpMYB10.1 and PpHY5 itself.

Progress on Understanding Transcriptional Regulation of Chloroplast Development in Fleshy Fruit

Edible fleshy fruits are important food sources in the human diet. Their yield and nutritional quality have long been considered as breeding targets for improvement. Various developing fleshy fruits with functional chloroplasts are capable of photosynthesis and contribute to fruit photosynthate, leading to the accumulation of metabolites associated with nutritional quality in ripe fruit. Although tomato high-pigment mutants with dark-green fruits have been isolated for more than 100 years, our understanding of the mechanism of chloroplast development in fleshy fruit remain poor. During the past few years, several transcription factors that regulate chloroplast development in fleshy fruit were identified through map-based cloning. In addition, substantial progress has been made in elucidating the mechanisms that how these transcription factors regulate chloroplast development. This review provides a summary and update on this progress, with a framework for further investigations of the multifaceted and hierarchical regulation of chloroplast development in fleshy fruit.

Molecular Evolution and Interaction of Membrane Transport and Photoreception in Plants

Light is a vital regulator that controls physiological and cellular responses to regulate plant growth, development, yield, and quality. Light is the driving force for electron and ion transport in the thylakoid membrane and other membranes of plant cells. In different plant species and cell types, light activates photoreceptors, thereby modulating plasma membrane transport. Plants maximize their growth and photosynthesis by facilitating the coordinated regulation of ion channels, pumps, and co-transporters across membranes to fine-tune nutrient uptake. The signal-transducing functions associated with membrane transporters, pumps, and channels impart a complex array of mechanisms to regulate plant responses to light. The identification of light responsive membrane transport components and understanding of their potential interaction with photoreceptors will elucidate how light-activated signaling pathways optimize plant growth, production, and nutrition to the prevailing environmental changes. This review summarizes the mechanisms underlying the physiological and molecular regulations of light-induced membrane transport and their potential interaction with photoreceptors in a plant evolutionary and nutrition context. It will shed new light on plant ecological conservation as well as agricultural production and crop quality, bringing potential nutrition and health benefits to humans and animals.

A perspective on ecologically relevant plant-UV research and its practical application

Plants perceive ultraviolet-B (UV-B) radiation through the UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8), and initiate regulatory responses via associated signalling networks, gene expression and metabolic pathways. Various regulatory adaptations to UV-B radiation enable plants to harvest information about fluctuations in UV-B irradiance and spectral composition in natural environments, and to defend themselves against UV-B exposure. Given that UVR8 is present across plant organs and tissues, knowledge of the systemic signalling involved in its activation and function throughout the plant is important for understanding the context of specific responses. Fine-scale understanding of both UV-B irradiance and perception within tissues and cells requires improved application of knowledge about UV-attenuation in leaves and canopies, warranting greater consideration when designing experiments. In this context, reciprocal crosstalk among photoreceptor-induced pathways also needs to be considered, as this appears to produce particularly complex patterns of physiological and morphological response. Through crosstalk, plant responses to UV-B radiation go beyond simply UV-protection or amelioration of damage, but may give cross-protection over a suite of environmental stressors. Overall, there is emerging knowledge showing how information captured by UVR8 is used to regulate molecular and physiological processes, although understanding of upscaling to higher levels of organisation, i.e. organisms, canopies and communities remains poor. Achieving this will require further studies using model plant species beyond Arabidopsis, and that represent a broad range of functional types. More attention should also be given to plants in natural environments in all their complexity, as such studies are needed to acquire an improved understanding of the impact of climate change in the context of plant-UV responses. Furthermore, broadening the scope of experiments into the regulation of plant-UV responses will facilitate the application of UV radiation in commercial plant production. By considering the progress made in plant-UV research, this perspective highlights prescient topics in plant-UV photobiology where future research efforts can profitably be focussed. This perspective also emphasises burgeoning interdisciplinary links that will assist in understanding of UV-B effects across organisational scales and gaps in knowledge that need to be filled so as to achieve an integrated vision of plant responses to UV-radiation.