Study on the immunomodulatory mechanism of vitamin D in patients with unexplained recurrent spontaneous abortion.

Background: To investigate the mechanism of vitamin D level on the regulation of peripheral blood lymphocyte subsets and serum Th1/Th2 cytokines in patients with unexplained recurrent spontaneous abortion (URSA). Methods: Eighty female patients with URSA attending Sichuan Jinxin Xinan Women's and Children's Hospital from January 2020 to May 2021 were selected as the study group, and 30 age-matched women with a history of healthy deliveries were chosen as the control group, and peripheral blood lymphocyte subpopulations and serum Th1/Th2 cytokines of people with different levels of vitamin D were detected in the study group by flow cytometry, respectively. The results of immune factors before and after supplementation were analyzed in 40 of these patients with low vitamin D levels. The results of lymphoid subpopulations and Th1/Th2 cytokines in 19 patients with normal pregnancy before and after vitamin D supplementation and after normal pregnancy were also analyzed comparatively. Results: (1) Serum 25(OH)D in the study group was lower than in the control group; peripheral blood Th cells, B cells and NK cells in the study group were higher than in the control group; IL-2, TNF-α, IFN-γ and IL-6 in the study group were higher than in the control group, while IL-4 and IL-10 in the study group were lower than in the control group (P < 0.05). (2) Th cells, B cells and NK cells of URSA patients in the vitamin D low level group were higher than those in the vitamin D normal group; serum cytokines IL-2, TNF-α and IFN-γ of patients in the vitamin D low level group were higher than those in the vitamin D normal group (P < 0.05); (3) Th cells, B cells and NK cells in URSA patients after vitamin D supplementation were lower than before vitamin D supplementation; serum cytokines IL-2, TNF-α and IFN-γ after vitamin D supplementation were lower than before vitamin D supplementation, IL-4 and IL-10 after vitamin D supplementation were higher than before vitamin D supplementation (P < 0.05), and there was no significant difference in IL-6 before and after vitamin D supplementation. (4) Th cells, B cells and NK cells in patients with normal pregnancy after vitamin D supplementation and after pregnancy were lower than those before vitamin D supplementation; serum cytokines IL-2, TNF-α and IFN-γ after vitamin D supplementation and after pregnancy were lower than those before vitamin D supplementation, and serum cytokines IL-4 and IL-10 after vitamin D supplementation and after pregnancy were higher than those before vitamin D supplementation, TNF -α, IFN-γ after pregnancy were lower than after vitamin D supplementation (P < 0.05), IL-6 was not significantly different before and after vitamin D supplementation and after pregnancy. Conclusion: Vitamin D deficiency rate was high in URSA patients. Th、B、NK cells and IL-2, TNF-α, IFN-γ, IL-6 cytokines were high, while IL-6 and IL-10 were low in URSA patients. IL-2, TNF-α, IFN-γ cytokines and Th, B, NK cells were increased in vitamin D deficient URSA patients, and Vitamin D deficiency may be an important cause or aggravating factor of immune dysfunction in URSA patients. Vitamin D has an immunomodulatory effect on URSA patients, promoting successful pregnancy by down-regulating peripheral blood Th, B, and NK cells and IL-2, TNF-α, and IFN-γ cytokines, while up-regulating IL-4 and IL-10.

Dysregulated low-density granulocyte contributes to early spontaneous abortion.

Spontaneous abortion (SA) is a common adverse pregnancy event with unclarified pathogenesis and limited therapeutic efficiency. Although most SA cases with the euploid embryo(s) are associated with immunological factors, the contribution of low-density granulocyte (LDG) in SA pathogenesis is rarely reported. This study aimed to investigate the serial characteristics and possible contribution of LDG and their subpopulations in early pregnancy, especially in early SA. Unpregnant (UP), normally pregnant (NP), and SA women were recruited, and the peripheral blood and endometrium/decidua were collected for LDG isolation and histological observation. The percentage, phenotype, and subpopulations of LDG were analyzed via flow cytometric analysis, and the ability of Nets formation was assessed by immunofluorescent and immunohistochemical assays. As a result, 43 participants were enrolled, including 10 UP, 15 NP, and 18 SA women. Compared with the UP group, the LDG percentage in peripheral blood mononuclear cells (PBMCs) and decidual immune cells (DICs) increased in the NP group, while the loss of this increase was observed in the SA group. Meanwhile, CD16int/- cell percentage in peripheral blood LDG (PB-LDG) increased in the NP and SA groups, and insufficient activation of CD16hi PB-LDG characterized by reduced CD11b expression was discovered in the SA group. Moreover, the LDG percentage in DICs was higher than that in PBMCs, and the decidual LDG (D-LDG) showed a surface marker expression profile that is easier to be activated in the pregnant cohort (NP + SA women). Finally, increased decidual Nets formation was observed in the SA group compared with the NP group, and more Nets formation was detected in D-LDG of NP and SA women following PMA stimulation. Overall, LDG participates in the maintenance of early pregnancy, while dysregulated LDG is responsible for early SA, providing novel potential targets for further exploration of SA pathogenesis and therapeutics.

Reciprocity between a retrograde signal and a putative metalloprotease reconfigures plastidial metabolic and structural states.

Reconfiguration of the plastidial proteome in response to environmental cues is central to tailoring adaptive responses. To define the underlying mechanisms and consequences of these reconfigurations, we performed a suppressor screen, using a mutant (ceh1) accumulating high levels of a plastidial retrograde signaling metabolite, MEcPP. We isolated a revertant partially suppressing the dwarf stature and high salicylic acid of ceh1 and identified the mutation in a putative plastidial metalloprotease (VIR3). Biochemical analyses showed increased VIR3 levels in ceh1, accompanied by reduced abundance of VIR3-target enzymes, ascorbate peroxidase, and glyceraldehyde 3-phophate dehydrogenase B. These proteomic shifts elicited increased H2O2, salicylic acid, and MEcPP levels, as well as stromule formation. High light recapitulated VIR3-associated reconfiguration of plastidial metabolic and structural states. These results establish a link between a plastidial stress-inducible retrograde signaling metabolite and a putative metalloprotease and reveal how the reciprocity between the two components modulates plastidial metabolic and structural states, shaping adaptive responses.

Comprehensive profile of circRNAs in formaldehyde induced heart development.

Circular RNAs (circRNAs) are a novel type of long non-coding RNAs that can regulate gene expression in heart development and heart disease. However, the expression pattern of circRNAs in congenital heart disease (CHD) induced by formaldehyde exposure is still unknown. We detected circRNAs expression profiles in heart tissue taken from six neonatal rat pups with formaldehyde exposure group and normal group using RNA-sequencing. Results revealed that a total of 54 circRNAs were dysregulated in the formaldehyde exposure group compared to the normal group. Among them, 31 were upregulated and 23 were downregulated (fold change = 2.0, p < 0.0 5). The qRT-qPCR results showed that expressions of 12:628708|632694, 18:77477060|77520779, 5:167486001|167526275 were significantly upregulated, while that of 7:41167312|4116775 and 20:50659751|5068786 were notably downregulated; the expression pattern was consistent with the RNA sequencing data. Bioinformatics analysis shows that the pathogenesis of formaldehyde exposure-induced CHD may involve Hippo-YAP pathway、Notch signaling pathway and other pathways. A key miRNA (rno-miR-665) was identified by constructing a circRNA-miRNA-mRNA co-expression network. In summary, the study illustrated that circRNAs differentially expressed in fetal heart tissues during formaldehyde exposure has potential biological functions and may be a biomarker or therapeutic target for CHD.

The cellular function and molecular mechanism of formaldehyde in cardiovascular disease and heart development.

As a common air pollutant, formaldehyde is widely present in nature, industrial production and consumer products. Endogenous formaldehyde is mainly produced through the oxidative deamination of methylamine catalysed by semicarbazide-sensitive amine oxidase (SSAO) and is ubiquitous in human body fluids, tissues and cells. Vascular endothelial cells and smooth muscle cells are rich in this formaldehyde-producing enzyme and are easily damaged owing to consequent cytotoxicity. Consistent with this, increasing evidence suggests that the cardiovascular system and stages of heart development are also susceptible to the harmful effects of formaldehyde. Exposure to formaldehyde from different sources can induce heart disease such as arrhythmia, myocardial infarction (MI), heart failure (HF) and atherosclerosis (AS). In particular, long-term exposure to high concentrations of formaldehyde in pregnant women is more likely to affect embryonic development and cause heart malformations than long-term exposure to low concentrations of formaldehyde. Specifically, the ability of mouse embryos to effect formaldehyde clearance is far lower than that of the rat embryos, more readily allowing its accumulation. Formaldehyde may also exert toxic effects on heart development by inducing oxidative stress and cardiomyocyte apoptosis. This review focuses on the current progress in understanding the influence and underlying mechanisms of formaldehyde on cardiovascular disease and heart development.

Nicotine: Regulatory roles and mechanisms in atherosclerosis progression.

Smoking is an independent risk factor for atherosclerosis. The smoke produced by tobacco burning contains more than 7000 chemicals, among which nicotine is closely related to the occurrence and development of atherosclerosis. Nicotine, a selective cholinergic agonist, accelerates the formation of atherosclerosis by stimulating nicotinic acetylcholine receptors (nAChRs) located in neuronal and non-neuronal tissues. This review introduces the pathogenesis of atherosclerosis and the mechanisms involving nicotine and its receptors. Herein, we focus on the various roles of nicotine in atherosclerosis, such as upregulation of growth factors, inflammation, and the dysfunction of endothelial cells, vascular smooth muscle cells (VSMC) as well as macrophages. In addition, nicotine can stimulate the generation of reactive oxygen species, cause abnormal lipid metabolism, and activate immune cells leading to the onset and progression of atherosclerosis. Exosomes, are currently a research hotspot, due to their important connections with macrophages and the VSMC, and may represent a novel application into future preventive treatment to promote the prevention of smoking-related atherosclerosis. In this review, we will elaborate on the regulatory mechanism of nicotine on atherosclerosis, as well as the effects of interference with nicotine receptors and the use of exosomes to prevent atherosclerosis development.

Targeting the epigenome in in-stent restenosis: from mechanisms to therapy.

Coronary artery disease (CAD) is one of the most common causes of death worldwide. The introduction of percutaneous revascularization has revolutionized the therapy of patients with CAD. Despite the advent of drug-eluting stents, restenosis remains the main challenge in treating patients with CAD. In-stent restenosis (ISR) indicates the reduction in lumen diameter after percutaneous coronary intervention, in which the vessel's lumen re-narrowing is attributed to the aberrant proliferation and migration of vascular smooth muscle cells (VSMCs) and dysregulation of endothelial cells (ECs). Increasing evidence has demonstrated that epigenetics is involved in the occurrence and progression of ISR. In this review, we provide the latest and comprehensive analysis of three separate but related epigenetic mechanisms regulating ISR, namely, DNA methylation, histone modification, and non-coding RNAs. Initially, we discuss the mechanism of restenosis. Furthermore, we discuss the biological mechanism underlying the diverse epigenetic modifications modulating gene expression and functions of VSMCs, as well as ECs in ISR. Finally, we discuss potential therapeutic targets of the small molecule inhibitors of cardiovascular epigenetic factors. A more detailed understanding of epigenetic regulation is essential for elucidating this complex biological process, which will assist in developing and improving ISR therapy.

ßII spectrin (SPTBN1): biological function and clinical potential in cancer and other diseases.

ßII spectrin, the most common isoform of non-erythrocyte spectrin, is a cytoskeleton protein present in all nucleated cells. Interestingly, ßII spectrin is essential for the development of various organs such as nerve, epithelium, inner ear, liver and heart. The functions of ßII spectrin include not only establishing and maintaining the cell structure but also regulating a variety of cellular functions, such as cell apoptosis, cell adhesion, cell spreading and cell cycle regulation. Notably, ßII spectrin dysfunction is associated with embryonic lethality and the DNA damage response. More recently, the detection of altered ßII spectrin expression in tumors indicated that ßII spectrin might be involved in the development and progression of cancer. Its mutations and disorders could result in developmental disabilities and various diseases. The versatile roles of ßII spectrin in disease have been examined in an increasing number of studies; nonetheless, the exact mechanisms of ßII spectrin are still poorly understood. Thus, we summarize the structural features and biological roles of ßII spectrin and discuss its molecular mechanisms and functions in development, homeostasis, regeneration and differentiation. This review highlight the potential effects of ßII spectrin dysfunction in cancer and other diseases, outstanding questions for the future investigation of therapeutic targets. The investigation of the regulatory mechanism of ßII spectrin signal inactivation and recovery may bring hope for future therapy of related diseases.

miR-153-3p Targets ßII Spectrin to Regulate Formaldehyde-Induced Cardiomyocyte Apoptosis.

Background: Formaldehyde (FA) is ubiquitous in the environment and can be transferred to the fetus through placental circulation, causing miscarriage and congenital heart disease (CHD). Studies have shown that ßII spectrin is necessary for cardiomyocyte survival and differentiation, and its loss leads to heart development defects and cardiomyocyte apoptosis. Additionally, previous studies have demonstrated that miRNA is essential in heart development and remodeling. However, whether miRNA regulates FA-induced CHD and cardiomyocyte apoptosis remains unclear. Methods: Using commercially available rat embryonic cardiomyocytes and a rat model of fetal cardiomyocyte apoptosis. Real-time quantitative PCR (RT-qPCR) and Western blot were performed to examine the level of miR-153-3p, ßII spectrin, caspase 7, cleaved caspase7, Bax, Bcl-2 expression in embryonic cardiomyocytes and a rat model of fetal cardiomyocyte apoptosis. Apoptotic cell populations were evaluated by flow cytometry and Tunel. Luciferase activity assay and RNA pull-down assay were used to detect the interaction between miR-153-3p and ßII spectrin. Masson's trichrome staining detects the degree of tissue fibrosis. Fluorescence in situ hybridization (FISH) and Immunohistochemistry were used to detect the expression of miR-153-3p and ßII spectrin in tissues. Results: Using commercially available rat embryonic cardiomyocytes and a rat model of fetal cardiomyocyte apoptosis, our studies indicate that miR-153-3p plays a regulatory role by directly targeting ßII spectrin to promote cardiomyocyte apoptosis. miR-153-3p mainly regulates cardiomyocyte apoptosis by regulating the expression of caspase7, further elucidating the importance of apoptosis in heart development. Finally, the results with our animal model revealed that targeting the miR-153-3p/ßII spectrin pathway effectively regulated FA-induced damage during heart development. Recovery experiments with miR-153-3p antagomir resulted in the reversal of FA-induced cardiomyocyte apoptosis and fetal cardiac fibrosis. Conclusion: This study investigated the molecular mechanism underpinning the role of ßII spectrin in FA-induced CHD and the associated upstream miRNA pathway. The study findings suggest that miR-153-3p may provide a potential target for the clinical diagnosis and treatment of CHD.

Light modulates the gravitropic responses through organ-specific PIFs and HY5 regulation of LAZY4 expression in Arabidopsis.

Light and gravity are two key environmental factors that control plant growth and architecture. However, the molecular basis of the coordination of light and gravity signaling in plants remains obscure. Here, we report that two classes of transcription factors, PHYTOCHROME INTERACTING FACTORS (PIFs) and ELONGATED HYPOCOTYL5 (HY5), can directly bind and activate the expression of LAZY4, a positive regulator of gravitropism in both shoots and roots in Arabidopsis In hypocotyls, light promotes degradation of PIFs to reduce LAZY4 expression, which inhibits the negative gravitropism of hypocotyls. LAZY4 overexpression can partially rescue the negative gravitropic phenotype of pifq in the dark without affecting amyloplast development. Our identification of the PIFs-LAZY4 regulatory module suggests the presence of another role for PIF proteins in gravitropism, in addition to a previous report demonstrating that PIFs positively regulate amyloplast development to promote negative gravitropism in hypocotyls. In roots, light promotes accumulation of HY5 proteins to activate expression of LAZY4, which promotes positive gravitropism in roots. Together, our data indicate that light exerts opposite regulation of LAZY4 expression in shoots and roots by mediating the protein levels of PIFs and HY5, respectively, to inhibit the negative gravitropism of shoots and promote positive gravitropism of roots in Arabidopsis.

Two E3 ligases antagonistically regulate the UV-B response in Arabidopsis.

Photomorphogenesis is a pivotal developmental strategy used by plants to respond to environmental light levels. During emergence from the soil and the establishment of photomorphogenesis, seedlings encounter increasing levels of UV-B irradiation and develop adaptive responses accordingly. However, the molecular mechanisms that orchestrate UV-B signaling cascades remain elusive. Here, we provide biochemical and genetic evidence that the prolonged signaling circuits of UV-B-induced photomorphogenesis involve two sets of E3 ligases and a transcription factor in Arabidopsis thaliana The UV-B-inducible protein RUP1/RUP2 associates with the CUL4-DDB1 scaffold to form an E3 ligase, which represses photomorphogenesis by mediating the degradation of HY5, the hub transcription factor in the light signaling pathway. Conversely, COP1 directly targets RUP1/RUP2 for ubiquitination and degradation, leading to balanced RUP1/RUP2 accumulation, alleviation of the COP1-HY5 interaction, and stabilization of HY5 protein. Therefore, our study reveals that these two E3-substrate modules, CUL4-DDB1-RUP1/RUP2-HY5 and COP1-RUP1/RUP2, constitute the repression and derepression machinery by which plants respond to prolonged UV-B irradiation in photomorphogenic development.

Initiation of ER Body Formation and Indole Glucosinolate Metabolism by the Plastidial Retrograde Signaling Metabolite, MEcPP.

Plants have evolved tightly regulated signaling networks to respond and adapt to environmental perturbations, but the nature of the signaling hub(s) involved have remained an enigma. We have previously established that methylerythritol cyclodiphosphate (MEcPP), a precursor of plastidial isoprenoids and a stress-specific retrograde signaling metabolite, enables cellular readjustments for high-order adaptive functions. Here, we specifically show that MEcPP promotes two Brassicaceae-specific traits, namely endoplasmic reticulum (ER) body formation and induction of indole glucosinolate (IGs) metabolism selectively, via transcriptional regulation of key regulators NAI1 for ER body formation and MYB51/122 for IGs biosynthesis). The specificity of MEcPP is further confirmed by the lack of induction of wound-inducible ER body genes as well as IGs by other altered methylerythritol phosphate pathway enzymes. Genetic analyses revealed MEcPP-mediated COI1-dependent induction of these traits. Moreover, MEcPP signaling integrates the biosynthesis and hydrolysis of IGs through induction of nitrile-specifier protein1 and reduction of the suppressor, ESM1, and production of simple nitriles as the bioactive end product. The findings position the plastidial metabolite, MEcPP, as the initiation hub, transducing signals to adjust the activity of hard-wired gene circuitry to expand phytochemical diversity and alter the associated subcellular structure required for functionality of the secondary metabolites, thereby tailoring plant stress responses.

The plastidial retrograde signal methyl erythritol cyclopyrophosphate is a regulator of salicylic acid and jasmonic acid crosstalk.

The exquisite harmony between hormones and their corresponding signaling pathways is central to prioritizing plant responses to simultaneous and/or successive environmental trepidations. The crosstalk between jasmonic acid (JA) and salicylic acid (SA) is an established effective mechanism that optimizes and tailors plant adaptive responses. However, the underlying regulatory modules of this crosstalk are largely unknown. Global transcriptomic analyses of mutant plants (ceh1) with elevated levels of the stress-induced plastidial retrograde signaling metabolite 2-C-methyl-D-erythritol cyclopyrophosphate (MEcPP) revealed robustly induced JA marker genes, expected to be suppressed by the presence of constitutively high SA levels in the mutant background. Analyses of a range of genotypes with varying SA and MEcPP levels established the selective role of MEcPP-mediated signal(s) in induction of JA-responsive genes in the presence of elevated SA. Metabolic profiling revealed the presence of high levels of the JA precursor 12-oxo-phytodienoic acid (OPDA), but near wild type levels of JA in the ceh1 mutant plants. Analyses of coronatine-insensitive 1 (coi1)/ceh1 double mutant plants confirmed that the MEcPP-mediated induction is JA receptor COI1 dependent, potentially through elevated OPDA. These findings identify MEcPP as a previously unrecognized central regulatory module that induces JA-responsive genes in the presence of high SA, thereby staging a multifaceted plant response within the environmental context.

DWD HYPERSENSITIVE TO UV-B 1 is negatively involved in UV-B mediated cellular responses in Arabidopsis.

Among T-DNA insertion mutants of various cullin4-RING ubiquitin E3 ligase (CRL4) substrate receptors, one mutant that exhibits enhanced sensitivity in response to ultraviolet-B (UV-B) illumination has been isolated and its corresponding gene has been named DWD HYPERSENSITIVE TO UV-B 1 (DHU1) in Arabidopsis. dhu1 lines showed much shorter hypocotyls than those in wild type under low doses of UV-B. Other light did not alter hypocotyl growth patterns in dhu1, indicating the hypersensitivity of dhu1 is restricted to UV-B. DHU1 was upregulated by more than two times in response to UV-B application of 1.5 µmol m(-2) s(-1), implying its possible involvement in UV-B signaling. DHU1 is able to bind to DDB1, an adaptor of CRL4; accordingly, DHU1 is thought to act as a substrate receptor of CRL4. Microarray data generated from wild-type and dhu1 under low doses of UV-B revealed that 209 or 124 genes were upregulated or downregulated by more than two times in dhu1 relative to wild type, respectively. About 23.4 % of the total upregulated genes in dhu1 were upregulated by more than five times in response to UV-B based on the AtGenExpress Visualization Tool data, while only about 1.4 % were downregulated to the same degree by UV-B, indicating that loss of DHU1 led to the overall enhancement of the upregulation of UV-B inducible genes. dhu1 also showed altered responsiveness under high doses of UV-B. Taken together, these findings indicate that DHU1 is a potent CRL4 substrate receptor that may function as a negative regulator of UV-B response in Arabidopsis.

Coordinated photomorphogenic UV-B signaling network captured by mathematical modeling.

Long-wavelength and low-fluence UV-B light is an informational signal known to induce photomorphogenic development in plants. Using the model plant Arabidopsis thaliana, a variety of factors involved in UV-B-specific signaling have been experimentally characterized over the past decade, including the UV-B light receptor UV resistance locus 8; the positive regulators constitutive photomorphogenesis 1 and elongated hypocotyl 5; and the negative regulators cullin4, repressor of UV-B photomorphogenesis 1 (RUP1), and RUP2. Individual genetic and molecular studies have revealed that these proteins function in either positive or negative regulatory capacities for the sufficient and balanced transduction of photomorphogenic UV-B signal. Less is known, however, regarding how these signaling events are systematically linked. In our study, we use a systems biology approach to investigate the dynamic behaviors and correlations of multiple signaling components involved in Arabidopsis UV-B-induced photomorphogenesis. We define a mathematical representation of photomorphogenic UV-B signaling at a temporal scale. Supplemented with experimental validation, our computational modeling demonstrates the functional interaction that occurs among different protein complexes in early and prolonged response to photomorphogenic UV-B.

Photoactivated UVR8-COP1 module determines photomorphogenic UV-B signaling output in Arabidopsis.

In Arabidopsis, ultraviolet (UV)-B-induced photomorphogenesis is initiated by a unique photoreceptor UV resistance locus 8 (UVR8) which utilizes its tryptophan residues as internal chromophore to sense UV-B. As a result of UV-B light perception, the UVR8 homodimer shaped by its arginine residues undergoes a conformational switch of monomerization. Then UVR8 associates with the constitutively photomorphogenic 1-suppressor of PHYA (COP1-SPA) core complex(es) that is released from the cullin 4-damaged dna binding protein 1 (CUL4-DDB1) E3 apparatus. This association, in turn, causes COP1 to convert from a repressor to a promoter of photomorphogenesis. It is not fully understood, however, regarding the biological significance of light-absorbing and dimer-stabilizing residues for UVR8 activity in photomorphogenic UV-B signaling. Here, we take advantage of transgenic UVR8 variants to demonstrate that two light-absorbing tryptophans, W233 and W285, and two dimer-stabilizing arginines, R286 and R338, play pivotal roles in UV-B-induced photomorphogenesis. Mutation of each residue results in alterations in UV-B light perception, UVR8 monomerization and UVR8-COP1 association in response to photomorphogenic UV-B. We also identify and functionally characterize two constitutively active UVR8 variants, UVR8W285A and UVR8R338A, whose photobiological activities are enhanced by the repression of CUL4, a negative regulator in this pathway. Based on our molecular and biochemical evidence, we propose that the UVR8-COP1 affinity in plants critically determines the photomorphogenic UV-B signal transduction coupling with UVR8-mediated UV-B light perception.

Conversion from CUL4-based COP1-SPA E3 apparatus to UVR8-COP1-SPA complexes underlies a distinct biochemical function of COP1 under UV-B.

The evolutionarily conserved constitutive photomorphogenesis 1 (COP1) is a RING and WD40 protein that functions as a substrate receptor of CULLIN4-damaged DNA binding protein 1 (CUL4-DDB1)-based E3 ubiquitin ligases in both plants and animals. In Arabidopsis, COP1 is a central repressor of photomorphogenesis in the form of COP1-suppressor of PHYA (SPA) complex(es). CUL4-DDB1-COP1-SPA suppresses the photomorphogenic program by targeting the transcription factor elongated hypocotyl 5 for degradation. Intriguingly, under photomorphogenic UV-B light, COP1 reverses its repressive role and promotes photomorphogenesis. However, the mechanism by which COP1 is functionally switched is still obscure. Here, we demonstrate that UV-B triggers the physical and functional disassociation of the COP1-SPA core complex(es) from CUL4-DDB1 and the formation of a unique complex(es) containing the UV-B receptor UV resistance locus 8 (UVR8). The establishment of this UV-B-dependent COP1 complex(es) is associated with its positive modulation of elongated hypocotyl 5 stability and activity, which sheds light on the mechanism of COP1's promotive action in UV-B-induced photomorphogenesis.

Arabidopsis FHY3 and HY5 positively mediate induction of COP1 transcription in response to photomorphogenic UV-B light.

As sessile organisms, higher plants have evolved the capacity to sense and interpret diverse light signals to modulate their development. In Arabidopsis thaliana, low-intensity and long-wavelength UV-B light is perceived as an informational signal to mediate UV-B-induced photomorphogenesis. Here, we report that the multifunctional E3 ubiquitin ligase, CONSTITUTIVE PHOTOMORPHOGENESIS1 (COP1), a known key player in UV-B photomorphogenic responses, is also a UV-B-inducible gene. Two transcription factors, FAR-RED ELONGATED HYPOCOTYL3 (FHY3) and ELONGATED HYPOCOTYL5 (HY5), directly bind to distinct regulatory elements within the COP1 promoter, which are essential for the induction of the COP1 gene mediated by photomorphogenic UV-B signaling. Absence of FHY3 results in impaired UV-B-induced hypocotyl growth and reduced tolerance against damaging UV-B. Thus, FHY3 positively regulates UV-B-induced photomorphogenesis by directly activating COP1 transcription, while HY5 promotes COP1 expression via a positive feedback loop. Furthermore, FHY3 and HY5 physically interact with each other, and this interaction is diminished by UV-B. Together, our findings reveal that COP1 gene expression in response to photomorphogenic UV-B is controlled by a combinatorial regulation of FHY3 and HY5, and this UV-B-specific working mode of FHY3 and HY5 is distinct from that in far-red light and circadian conditions.

Structural basis of ultraviolet-B perception by UVR8.

The Arabidopsis thaliana protein UVR8 is a photoreceptor for ultraviolet-B. Upon ultraviolet-B irradiation, UVR8 undergoes an immediate switch from homodimer to monomer, which triggers a signalling pathway for ultraviolet protection. The mechanism by which UVR8 senses ultraviolet-B remains largely unknown. Here we report the crystal structure of UVR8 at 1.8 Å resolution, revealing a symmetric homodimer of seven-bladed ß-propeller that is devoid of any external cofactor as the chromophore. Arginine residues that stabilize the homodimeric interface, principally Arg 286 and Arg 338, make elaborate intramolecular cation-π interactions with surrounding tryptophan amino acids. Two of these tryptophans, Trp 285 and Trp 233, collectively serve as the ultraviolet-B chromophore. Our structural and biochemical analyses identify the molecular mechanism for UVR8-mediated ultraviolet-B perception, in which ultraviolet-B radiation results in destabilization of the intramolecular cation-π interactions, causing disruption of the critical intermolecular hydrogen bonds mediated by Arg 286 and Arg 338 and subsequent dissociation of the UVR8 homodimer.