Engineered bacterium-metal-organic framework biohybrids for boosting radiotherapy with multiple effects.

Hypoxia and lactate-overexpressed tumor microenvironment always lead to poor therapeutic effect of radiotherapy. Here, platinum nanoparticles-embellished hafnium metal-organic framework (Hf-MOF-Pt NPs) were elaborately integrated with Shewanella oneidensis MR-1 (SO) to construct an engineered biohybrid platform (SO@Hf-MOF-Pt) for enhancing radiotherapy. Benefiting from the tumor-targeting and metabolic respiration characteristics of SO, SO@Hf-MOF-Pt could enrich in tumor sites and continuously metabolize the overexpressed lactate, which specifically downregulated the expression of hypoxia-inducible factor (HIF-1α), thereby relieving the radiosuppressive tumor microenvironment to some extent. Moreover, SO@Hf-MOF-Pt would react with tumor-overexpressed hydrogen peroxide (H2O2) to generate oxygen (O2) and further inhibit the expression of HIF-1α, resulting in the downregulation of lactate dehydrogenase (LDHA) and subsequently reducing the lactate production. Under these multiple cascaded effects, the radiosuppressive tumor microenvironment was significantly reshaped, thus potentiating the radiosentization of SO@Hf-MOF-Pt and remarkably amplifying the therapeutic outcomes of radiotherapy. The designed biohybrid SO@Hf-MOF-Pt represented promising prospects in sensitizing radiotherapy via bacterium-based metabolic regulation.

Anion Receptor-manipulated solvation chemistry and electric double layer enables high Zn-Utilization rate and lean Zn metal batteries.

The practical application of aqueous Zn metal batteries (AZMBs) is impeded by inferior reversibility and stability of Zn metal anode (ZMA) originated from side reactions and dendrite growth. Herein, anion receptor l-Proline (LP) is selected to simultaneously manipulate solvation chemistry and electric double layer (EDL) for constructing dendrite-free and stable AZMBs with an ultra-high depth of discharge (DOD of 100 %) and low negative/positive capacity ratio (N/P of 1.1). Experimental and computational results demonstrate that the strong interaction between -SO32- group from OTf- anion and LP promotes the coordination effect of cation and solvent, which improves the stability of electrolyte and induces fine and uniform Zn nucleus formation. Meanwhile, the preferential reduction of OTf- and adsorption of LP establish an anion-derived ZnF2-rich solid electrolyte interface by altering EDL structure, which enhances the mechanical stability and Zn2+ diffusion kinetics of the interface and prevents the contact of H2O molecules. Consequently, ZMA in LP/Zn(OTf)2 electrolyte delivers a satisfactory cycling lifespan under DOD of 100 % and an outstanding Coulombic efficiency of 99.93 % for 10,000 cycles at 10 mA cm-2. Moreover, Zn||Od-NH4V4O10 full cells with LP/Zn(OTf)2 electrolyte demonstrate excellent cycle stability at high cathode loading (20.412 mg), low N/P (1.1), and high temperature (50 °C).

Simultaneous production of CO and H2O2 by paired electrolysis coupling CO2 reduction and water oxidation.

Here, a novel paired electrolysis system is constructed, where fluorine-doped tin oxide glass serves as the anode for the water oxidation reaction to produce hydrogen peroxide (H2O2), and cobalt phthalocyanine (CoPc)/carbon nanotube (CNT) loaded carbon paper as the cathode for CO2 reduction to generate CO. This system demonstrates a high overall energy efficiency of 34%, where a faradaic efficiency exceeding 90% for CO2 reduction and 60% for water oxidation to H2O2 have been achieved, demonstrating significant energy savings of nearly 40% compared to the respective half-reaction systems.

Covalent Triazine-Based Frameworks with Ru-tda Based Catalyst Anchored via Coordination Bond for Photoinduced Water Oxidation.

Light-induced water splitting (hν-WS) for the production of hydrogen as a solar fuel is considered a promising sustainable strategy for the replacement of fossil fuels. An efficient system for hν-WS involves a photoactive material that, upon shining light, is capable of separating and transferring charges to catalysts for the hydrogen and oxygen evolution processes. Covalent triazine-based frameworks (CTFs) represent an interesting class of 2D organic light-absorbing materials that have recently emerged thanks to their tunable structural, optical and morphological properties. Typically, catalysts (Cat) are metallic nanoparticles generated in situ after photoelectroreduction of metal precursors or directly drop-casted on top of the CTF material to generate Cat-CTF assemblies. In this work, the synthesis, characterization and photocatalytic performance of a novel hybrid material, Ru-CTF, is reported, based on a CTF structure featuring dangling pyridyl groups that allow the Ru-tda (tda is [2,2':6',2'"-terpyridine]-6,6'"-dicarboxylic acid) water oxidation catalyst (WOC) unit to coordinate via covalent bond. The Ru-CTF molecular hybrid material can carry out the light-induced water oxidation reaction efficiently at neutral pH, reaching values of maximum TOF of 17 h-1 and TONs in the range of 220 using sodium persulfate as a sacrificial electron acceptor.

Supramolecular Anchoring of Fe(III) Molecular Redox Catalysts into Graphitic Surfaces Via CH-π and π-π Interactions for CO2 Electroreduction.

Photoelectrochemical devices require solid anodes and cathodes for the easy assembling of the whole cell and thus redox catalysts need to be deposited on the electrodes. Typical catalyst deposition involves drop casting, spin coating, doctor blading or related techniques to generate modified electrodes where the active catalyst in contact with the electrolyte is only a very small fraction of the deposited mass. We have developed a methodology where the redox catalyst is deposited at the electrode based on supramolecular interactions, namely CH-π and π-π between the catalyst and the surface. This generates a very well-defined catalysts-surface structure and electroactivity, together with a very large catalytic response. This approach represents a new anchoring strategy that can be applied to catalytic redox reactions in heterogeneous phase and compared to traditional methods involves about 4-5 orders of magnitude less mass deposition to achieve comparable activity and with very well-behaved electroactivity and stability.

[Magnetic stimulation combined with moxibustion improves mild to moderate overactive bladder and sexual function in women].

OBJECTIVE: To investigate the clinical effect of magnetic stimulation combined with moxibustion on mild to moderate overactive bladder (OAB) and sexual function in women. METHODS: We enrolled 80 female patients with mild to moderate OAB in this study and equally randomized them into a control and an experimental group, the former treated by magnetic stimulation and the latter by magnetic stimulation combined with moxibustion, both for 8 weeks. We obtained from the patients their OAB syndrome scores (OABSS), 72-hour urination diary (72-h UD) scores, International Consultation on Incontinence Questionnaire － Overactive Bladder (ICIQ-OAB) scores and female sexual function indexes (FSFI), and compared them between the two groups before and after intervention. RESULTS: A total of 77 patients completed the study, 37 in the control and 40 in the experimental group. There were no statistically significant differences in the baseline data between the two groups (P > 0.05). Compared with the baseline, the experimental group showed significant improvement after treatment in the OABSS (7.54±1.12 vs 4.46±0.96), 72-h urine volume (ï¼»126.40±46.04ï¼½ vs ï¼»216.63±38.26ï¼½ ml), urination frequency (15.55±3.21 vs 8.03±1.40), ICIQ-OAB score (10.25±1.15 vs 6.32±1.07) and FSFI (20.00±12.40 vs 33.30±21.00) (all P < 0.05), even more significantly than in the control group (OABSS: 4.46±0.96 vs 5.59±0.90; 72-h urine volume: ï¼»216.63±38.26ï¼½ vs ï¼»173.41±15.55ï¼½ ml; urination frequency: 8.03±1.40 vs 9.90±1.49; ICIQ-OAB score: 6.32±1.07 vs 7.89±0.77; FSFI: 33.30±21.00 vs 30.40±10.40) (all P < 0.01). CONCLUSION: Magnetic stimulation combined with moxibustion can improve the symptoms of mild to moderate overactive bladder and improve sexual function in females.

Exploring the Potential of Al(III) Photosensitizers for Energy Transfer Reactions.

Three homoleptic Al(III) complexes (Al1-Al3) with different degrees of methylation at the 2-pyridylpyrrolide ligand were systematically tested for their function as photosensitizers (PS) in two types of energy transfer reactions. First, in the generation of reactive singlet oxygen (1O2), and second, in the isomerization of (E)- to (Z)-stilbene. 1O2 was directly evidenced by its characteristic NIR emission at around 1276 nm and indirectly by the reaction with an organic substrate [e.g. 2,5-diphenylfuran (DPF)] using in situ UV/vis spectroscopy. In a previous study, the presence of additional methyl groups was found to be beneficial for the photocatalytic reduction of CO2 to CO, but here Al1 without any methyl groups exhibits superior performance. To rationalize this behavior, a combination of photophysical experiments (absorption, emission and excited state lifetimes) together with photostability measurements and scalar-relativistic time-dependent density functional theory calculations was applied. As a result, Al1 exhibited the highest emission quantum yield (64%), the longest emission lifetime (8.7 ns) and the best photostability under the reaction conditions required for the energy transfer reactions (e.g. in aerated chloroform). Moreover, Al1 provided the highest rate constant (0.043 min-1) for the photocatalytic oxygenation of DPF, outperforming even noble metal-based competitors such as [Ru(bpy)3]2+. Finally, its superior photostability enabled a long-term test (7 h), in which Al1 was successfully recycled seven times, underlining the high potential of this new class of earth-abundant PSs.

A strategy to distinguish similar traditional Chinese medicines by liquid chromatography-mass spectrometry, electronic senses, and gas chromatography-ion mobility spectrometry: Marsdeniae tenacissimae Caulis and Paederiae scandens Caulis as examples.

INTRODUCTION: Marsdeniae tenacissimae Caulis (MTC), a popular traditional Chinese medicine, has been widely used in the treatment of tumor diseases. Paederiae scandens Caulis (PSC), which is similar in appearance to MTC, is a common counterfeit product. It is difficult for traditional methods to effectively distinguish between MTC and PSC. Therefore, there is an urgent need for a rapid and accurate method to identify MTC and PSC. OBJECTIVES: The aim is to distinguish between MTC and PSC by analyzing the differences in nonvolatile organic compounds (NVOCs), taste, odor, and volatile organic compounds (VOCs). METHODS: Liquid chromatography-mass spectrometry (LC-MS) was utilized to analyze the NVOCs of MTC and PSC. Electronic tongue (E-tongue) and electronic nose (E-nose) were used to analyze their taste and odor respectively. Gas chromatography-ion mobility spectrometry (GC-IMS) was applied to analyze VOCs. Finally, multivariate statistical analyses were conducted to further investigate the differences between MTC and PSC, including principal component analysis, orthogonal partial least squares discriminant analysis, discriminant factor analysis, and soft independent modeling of class analysis. RESULTS: The results of this study indicate that the integrated strategy of LC-MS, E-tongue, E-nose, GC-IMS, and multivariate statistical analysis can be effectively applied to distinguish between MTC and PSC. Using LC-MS, 25 NVOCs were identified in MTC, while 18 NVOCs were identified in PSC. The major compounds in MTC are steroids, while the major compounds in PSC are iridoid glycosides. Similarly, the distinct taste difference between MTC and PSC was precisely revealed by the E-tongue. Specifically, the pronounced bitterness in PSC was proven to stem from iridoid glycosides, whereas the bitterness evident in MTC was intimately tied to steroids. The E-nose detected eight odor components in MTC and six in PSC, respectively. The subsequent statistical analysis uncovered notable differences in their odor profiles. GC-IMS provided a visual representation of the differences in VOCs between MTC and PSC. The results indicated a relatively high relative content of 82 VOCs in MTC, contrasted with 32 VOCs exhibiting a similarly high relative content in PSC. CONCLUSION: In this study, for the first time, the combined use of LC-MS, E-tongue, E-nose, GC-IMS, and multivariate statistical analysis has proven to be an effective method for distinguishing between MTC and PSC from multiple perspectives. This approach provides a valuable reference for the identification of other visually similar traditional Chinese medicines.

Interference of ATP-Adenosine Axis by Engineered Biohybrid for Amplifying Immunogenic Cell Death-Mediated Antitumor Immunotherapy.

Immunogenic cell death (ICD) often results in the production and accumulation of adenosine (ADO), a byproduct that negatively impacts the therapeutic effect as well as facilitates tumor development and metastasis. Here, an innovative strategy is elaborately developed to effectively activate ICD while avoiding the generation of immunosuppressive adenosine. Specifically, ZIF-90, an ATP-responsive consumer, is synthesized as the core carrier to encapsulate AB680 (CD73 inhibitor) and then coated with an iron-polyphenol layer to prepare the ICD inducer (AZTF), which is further grafted onto prebiotic bacteria via the esterification reaction to obtain the engineered biohybrid (Bc@AZTF). Particularly, the designed Bc@AZTF can actively enrich in tumor sites and respond to the acidic tumor microenvironment to offload AZTF nanoparticles, which can consume intracellular ATP (iATP) content and simultaneously inhibit the ATP-adenosine axis to reduce the accumulation of adenosine, thereby alleviating adenosine-mediated immunosuppression and strikingly amplifying ICD effect. Importantly, the synergy of anti-PD-1 (αPD-1) with Bc@AZTF not only establishes a collaborative antitumor immune network to potentiate effective tumoricidal immunity but also activates long-lasting immune memory effects to manage tumor recurrence and rechallenge, presenting a new paradigm for ICD treatment combined with adenosine metabolism.

Plant regeneration in the new era: from molecular mechanisms to biotechnology applications.

Plants or tissues can be regenerated through various pathways. Like animal regeneration, cell totipotency and pluripotency are the molecular basis of plant regeneration. Detailed systematic studies on Arabidopsis thaliana gradually unravel the fundamental mechanisms and principles underlying plant regeneration. Specifically, plant hormones, cell division, epigenetic remodeling, and transcription factors play crucial roles in reprogramming somatic cells and reestablishing meristematic cells. Recent research on basal non-vascular plants and monocot crops has revealed that plant regeneration differs among species, with various plant species using distinct mechanisms and displaying significant differences in regenerative capacity. Conducting multi-omics studies at the single-cell level, tracking plant regeneration processes in real-time, and deciphering the natural variation in regenerative capacity will ultimately help understand the essence of plant regeneration, improve crop regeneration efficiency, and contribute to future crop design.

Recent progress on nickel phthalocyanine-based electrocatalysts for CO2 reduction.

The electrocatalytic reduction of CO2 to high-value fuels by renewable electricity is a sustainable strategy, which can substitute for fossil fuels and circumvent climate changes induced by elevated CO2 emission levels, making the rational design of versatile electrocatalysts highly desirable. Among all the electrocatalytic materials used in the CO2 reduction reaction, nickel phthalocyanine (NiPc)-based electrocatalysts have attracted considerable attention recently because of their high CO selectivity and catalytic activity. Herein, we review the latest advances in CO2 electroreduction to CO catalyzed by immobilized NiPc and its derivatives on diverse surfaces. Specific strategies, the structure-performance relationship and the CO2-to-CO reaction mechanism of these NiPc-based electrocatalysts are analyzed. Future opportunities and challenges for this series of powerful heterogeneous electrocatalysts are also highlighted.

Highly Efficient, Noble-Metal-Free, Fully Aqueous CO2 Photoreduction Sensitized by a Robust Organic Dye.

The development of efficient, selective, and durable CO2 photoreduction systems presents a long-standing challenge in full aqueous solutions owing to the presence of scarce CO2 and the fierce competition against H2 evolution, which is even more challenging when noble metals are not utilized. Herein, we present the facile decorations of four phosphonic acid groups on a donor-acceptor-type organic dye to obtain a water-soluble photosensitizer (4P-DPAIPN), which succeeds the excellent photophysical and photoredox properties of its prototype, exhibiting long-lived delayed fluorescence (>10 µs) in aqueous solutions. Combining 4P-DPAIPN with a cationic cobalt porphyrin catalyst has accomplished record-high apparent quantum yields of 9.4-17.4% at 450 nm for CO2-to-CO photoconversion among the precedented systems (maximum 13%) in fully aqueous solutions. Remarkable selectivity of 82-93% and turnover number of 2700 for CO production can also be achieved with this noble-metal-free system, outperforming a benchmarking ruthenium photosensitizer and a commercial organic dye under parallel conditions. Such high performances of 4P-DPAIPN can be well maintained under real sunlight. More impressively, no significant decomposition of 4P-DPAIPN was detected during the long-term photocatalysis. Eventually, the photoinduced electron transfer pathways were proposed.

In Situ Sprayed Exosome-Cross-Linked Gel as Artificial Lymph Nodes for Postoperative Glioblastoma Immunotherapy.

One key challenge in postoperative glioblastoma immunotherapy is to guarantee a potent and durable T-cell response, which is restricted by the immunosuppressive microenvironment within the lymph nodes (LNs). Here, we develop an in situ sprayed exosome-cross-linked gel that acts as an artificial LN structure to directly activate the tumor-infiltrating T cells for prevention of glioma recurrence. Briefly, this gel is generated by a bio-orthogonal reaction between azide-modified chimeric exosomes and alkyne-modified alginate polymers. Particularly, these chimeric exosomes are generated from dendritic cell (DC)-tumor hybrid cells, allowing for direct and robust T-cell activation. The gel structure with chimeric exosomes as cross-linking points avoids the quick clearance by the immune system and thus prolongs the durability of antitumor T-cell immunity. Importantly, this exosome-containing immunotherapeutic gel provides chances for ameliorating functions of antigen-presenting cells (APCs) through accommodating different intracellular-acting adjuvants, such as stimulator of interferon genes (STING) agonists. This further enhances the antitumor T-cell response, resulting in the almost complete elimination of residual lesions after surgery. Our findings provide a promising strategy for postsurgical glioma immunotherapy that warrants further exploration in the clinical arena.

Reciprocal conversion between annual and polycarpic perennial flowering behavior in the Brassicaceae.

The development of perennial crops holds great promise for sustainable agriculture and food security. However, the evolution of the transition between perenniality and annuality is poorly understood. Here, using two Brassicaceae species, Crucihimalaya himalaica and Erysimum nevadense, as polycarpic perennial models, we reveal that the transition from polycarpic perennial to biennial and annual flowering behavior is a continuum determined by the dosage of three closely related MADS-box genes. Diversification of the expression patterns, functional strengths, and combinations of these genes endows species with the potential to adopt various life-history strategies. Remarkably, we find that a single gene among these three is sufficient to convert winter-annual or annual Brassicaceae plants into polycarpic perennial flowering plants. Our work delineates a genetic basis for the evolution of diverse life-history strategies in plants and lays the groundwork for the generation of diverse perennial Brassicaceae crops in the future.

[Effect of Thermal Hydrolysis Pretreatment Time on Microbial Community Structure in Sludge Anaerobic Digestion System].

To evaluate the effect of thermal hydrolysis pretreatment time on the sludge anaerobic digestion system of wastewater treatment plants (WWTPs) in Daxing district, Beijing, the structure and diversity of microbial communities in primary sludge and an activated sludge anaerobic digestion system with different thermal hydrolysis pretreatment times (15 min, 30 min, and 45 min) were analyzed using Illumina MiSeq high-throughput sequencing. The results showed that the dominant groups of digested sludge were mainly distributed in Firmicutes, Cloacimonadota, Chloroflexi, and Synergistota, with W5 being the most common genus. The sum of relative abundance of the dominant phylum was greater than 60%, and W5 accounted for 20.8%-54.5%, showing a high abundance of a few dominant species. During the anaerobic digestion of thermo-hydrolyzed sludge, the relative abundance of acetogenic methanogens decreased due to high levels of volatile fatty acids (VFAs) and ammonia nitrogen (NH4+-N) concentrations, which suggested that the hydrogenophilic methanogenic pathway was more than that of the acetogenic methanogenic pathway. Correlation analysis showed that the soluble protein and pH of thermo-hydrolyzed sludge, NH4+-N of digested sludge, and thermal hydrolysis pretreatment time were the four main environmental factors affecting microbial community structure, and NH4+-N of digested sludge had the largest negative correlation with methanogens. The thermal hydrolysis pretreatment time was negatively correlated with both the Chao index and Shannon index, so longer thermal hydrolysis pretreatment time was not conducive to microbial flora during anaerobic digestion.

Facile Access to High Solid Content Monodispersed Microspheres via Dual-Component Surfactants Regulation toward High-Performance Colloidal Photonic Crystals.

Monodispersed microspheres play a major role in optical science and engineering, providing ideal building blocks for structural color materials. However, the method toward high solid content (HSC) monodispersed microspheres has remained a key hurdle. Herein, a facile access to harvest monodispersed microspheres based on the emulsion polymerization mechanism is demonstrated, where anionic and nonionic surfactants are employed to achieve the electrostatic and steric dual-stabilization balance in a synergistic manner. Monodispersed poly(styrene-butyl acrylate-methacrylic acid) colloidal latex with 55 wt% HSC is achieved, which shows an enhanced self-assembly efficiency of 280% compared with the low solid content (10 wt%) latex. In addition, Ag-coated colloidal photonic crystal (Ag@CPC) coating with near-zero refractive index is achieved, presenting the characteristics of metamaterials. And an 11-fold photoluminescence emission enhancement of CdSe@ZnS quantum dots is realized by the Ag@CPC metamaterial coating. Taking advantage of high assembly efficiency, easily large-scale film-forming of the 55 wt% HSC microspheres latex, robust Ag@CPC metamaterial coatings could be easily produced for passive cooling. The coating demonstrates excellent thermal insulation performance with theoretical cooling power of 30.4 W m-2, providing practical significance for scalable CPC architecture coatings in passive cooling.

Highly efficient electrocatalytic CO2 reduction by a CrIII quaterpyridine complex.

Design tactics and mechanistic studies both remain as fundamental challenges during the exploitations of earth-abundant molecular electrocatalysts for CO2 reduction, especially for the rarely studied Cr-based ones. Herein, a quaterpyridyl CrIII catalyst is found to be highly active for CO2 electroreduction to CO with 99.8% Faradaic efficiency in DMF/phenol medium. A nearly one order of magnitude higher turnover frequency (86.6 s-1) over the documented Cr-based catalysts (<10 s-1) can be achieved at an applied overpotential of only 190 mV which is generally 300 mV lower than these precedents. Such a high performance at this low driving force originates from the metal-ligand cooperativity that stabilizes the low-valent intermediates and serves as an efficient electron reservoir. Moreover, a synergy of electrochemistry, spectroelectrochemistry, electron paramagnetic resonance, and quantum chemical calculations allows to characterize the key CrII, CrI, Cr0, and CO-bound Cr0 intermediates as well as to verify the catalytic mechanism.

Directed Electron Delivery from a Pb-Free Halide Perovskite to a Co(II) Molecular Catalyst Boosts CO2 Photoreduction Coupled with Water Oxidation.

The development of high-performance photocatalytic systems for CO2 reduction is appealing to address energy and environmental issues, while it is challenging to avoid using toxic metals and organic sacrificial reagents. We here immobilize a family of cobalt phthalocyanine catalysts on Pb-free halide perovskite Cs2AgBiBr6 nanosheets with delicate control on the anchors of the cobalt catalysts. Among them, the molecular hybrid photocatalyst assembled by carboxyl anchors achieves the optimal performance with an electron consumption rate of 300±13 µmol g-1 h-1 for visible-light-driven CO2-to-CO conversion coupled with water oxidation to O2, over 8 times of the unmodified Cs2AgBiBr6 (36±8 µmol g-1 h-1), also far surpassing the documented systems (<150 µmol g-1 h-1). Besides the improved intrinsic activity, electrochemical, computational, ex-/in situ X-ray photoelectron and X-ray absorption spectroscopic results indicate that the electrons photogenerated at the Bi atoms of Cs2AgBiBr6 can be directionally transferred to the cobalt catalyst via the carboxyl anchors which strongly bind to the Bi atoms, substantially facilitating the interfacial electron transfer kinetics and thereby the photocatalysis.

Flowering time: From physiology, through genetics to mechanism.

Plant species have evolved different requirements for environmental/endogenous cues to induce flowering. Originally, these varying requirements were thought to reflect the action of different molecular mechanisms. Thinking changed when genetic and molecular analysis in Arabidopsis thaliana revealed that a network of environmental and endogenous signaling input pathways converge to regulate a common set of "floral pathway integrators." Variation in the predominance of the different input pathways within a network can generate the diversity of requirements observed in different species. Many genes identified by flowering time mutants were found to encode general developmental and gene regulators, with their targets having a specific flowering function. Studies of natural variation in flowering were more successful at identifying genes acting as nodes in the network central to adaptation and domestication. Attention has now turned to mechanistic dissection of flowering time gene function and how that has changed during adaptation. This will inform breeding strategies for climate-proof crops and help define which genes act as critical flowering nodes in many other species.

The structure of B-ARR reveals the molecular basis of transcriptional activation by cytokinin.

The phytohormone cytokinin has various roles in plant development, including meristem maintenance, vascular differentiation, leaf senescence, and regeneration. Prior investigations have revealed that cytokinin acts via a phosphorelay similar to the two-component system by which bacteria sense and respond to external stimuli. The eventual targets of this phosphorelay are type-B ARABIDOPSIS RESPONSE REGULATORS (B-ARRs), containing the conserved N-terminal receiver domain (RD), middle DNA binding domain (DBD), and C-terminal transactivation domain. While it has been established for two decades that the phosphoryl transfer from a specific histidyl residue in ARABIDOPSIS HIS PHOSPHOTRANSFER PROTEINS (AHPs) to an aspartyl residue in the RD of B-ARRs results in a rapid transcriptional response to cytokinin, the underlying molecular basis remains unclear. In this work, we determine the crystal structures of the RD-DBD of ARR1 (ARR1RD-DBD) as well as the ARR1DBD-DNA complex from Arabidopsis. Analyses of the ARR1DBD-DNA complex have revealed the structural basis for sequence-specific recognition of the GAT trinucleotide by ARR1. In particular, comparing the ARR1RD-DBD and ARR1DBD-DNA structures reveals that unphosphorylated ARR1RD-DBD exists in a closed conformation with extensive contacts between the RD and DBD. In vitro and vivo functional assays have further suggested that phosphorylation of the RD weakens its interaction with DBD, subsequently permits the DNA binding capacity of DBD, and promotes the transcriptional activity of ARR1. Our findings thus provide mechanistic insights into phosphorelay activation of gene transcription in response to cytokinin.