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

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

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

BACKGROUND: B-box (BBX) proteins play important roles in regulating plant growth, development, and abiotic stress responses. BBX family genes have been identified and functionally characterized in many plant species, but little is known about the BBX family in blueberry (Vaccinium corymbosum). RESULT: In this study, we identified 23 VcBBX genes from the Genome Database for Vaccinium (GDV). These VcBBXs can be divided into five clades based on gene structures and conserved domains in their encoded proteins. The prediction of cis-acting elements in the upstream sequences of VcBBX genes and protein-protein interactions indicated that VcBBX proteins are likely involved in phytohormone signaling pathways and abiotic stress responses. Analysis of transcriptome deep sequencing (RNA-seq) data showed that VcBBX genes exhibited organ-specific expression pattern and 11 VcBBX genes respond to ultraviolet B (UV-B) radiation. The co-expression analysis revealed that the encoded 11 VcBBX proteins act as bridges integrating UV-B and phytohormone signaling pathways in blueberry under UV-B radiation. Reverse-transcription quantitative PCR (RT-qPCR) analysis showed that most VcBBX genes respond to drought, salt, and cold stress. Among VcBBX proteins, VcBBX24 is highly expressed in all the organs, not only responds to abiotic stress, but it also interacts with proteins in UV-B and phytohormone signaling pathways, as revealed by computational analysis and co-expression analysis, and might be an important regulator integrating abiotic stress and phytohormone signaling networks. CONCLUSIONS: Twenty-three VcBBX genes were identified in blueberry, in which, 11 VcBBX genes respond to UV-B radiation, and act as bridges integrating UV-B and phytohormone signaling pathways according to RNA-seq data. The expression patterns under abiotic stress suggested that the functional roles of most VcBBX genes respose to drought, salt, and cold stress. Our study provides a useful reference for functional analysis of VcBBX genes and for improving abiotic stress tolerance in blueberry.

Solution-Processed Hybrid Europium (II) Iodide Scintillator for Sensitive X-Ray Detection.

Lead halide perovskite nanocrystals have recently demonstrated great potential as x-ray scintillators, yet they still suffer toxicity issues, inferior light yield (LY) caused by severe self-absorption. Nontoxic bivalent europium ions (Eu2+) with intrinsically efficient and self-absorption-free d-f transition are a prospective replacement for the toxic Pb2+. Here, we demonstrated solution-processed organic-inorganic hybrid halide BA10EuI12 (BA denotes C4H9NH4+) single crystals for the first time. BA10EuI12 was crystallized in a monoclinic space group of P21/c, with photoactive sites of [EuI6]4- octahedra isolated by BA+ cations, which exhibited high photoluminescence quantum yield of 72.5% and large Stokes shift of 97 nm. These properties enable an appreciable LY value of 79.6% of LYSO (equivalent to ~27,000 photons per MeV) for BA10EuI12. Moreover, BA10EuI12 shows a short excited-state lifetime (151 ns) due to the parity-allowed d-f transition, which boosts the potential of BA10EuI12 for use in real-time dynamic imaging and computer tomography applications. In addition, BA10EuI12 demonstrates a decent linear scintillation response ranging from 9.21 µGyair s-1 to 145 µGyair s-1 and a detection limit as low as 5.83 nGyair s-1. The x-ray imaging measurement was performed using BA10EuI12 polystyrene (PS) composite film as a scintillation screen, which exhibited clear images of objects under x-ray irradiation. The spatial resolution was determined to be 8.95 lp mm-1 at modulation transfer function = 0.2 for BA10EuI12/PS composite scintillation screen. We anticipate that this work will stimulate the exploration of d-f transition lanthanide metal halides for sensitive x-ray scintillators.

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

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

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

Ultraviolet-B (UV-B) radiation is an environmental signal that affects the accumulation of secondary metabolites in plants. In particular, UV-B promotes flavonoid biosynthesis, leading to improved fruit quality. To explore the underlying molecular mechanism, we exposed blueberry (Vaccinium corymbosum) calli to UV-B radiation and performed a transcriptome deep sequencing (RNA-seq) analysis to identify differentially expressed genes (DEGs). We detected 16,899 DEGs among different treatments, with the largest number seen after 24 h of UV-B exposure relative to controls. Functional annotation and enrichment analysis showed a significant enrichment for DEGs in pathways related to plant hormone signal transduction and phenylpropanoid and flavonoid biosynthesis. In agreement with the transcriptome data, flavonol, anthocyanin and proanthocyanidin accumulated upon UV-B radiation, and most DEGs mapping to the phenylpropanoid and flavonoid biosynthetic pathways using the KEGG mapper tool were upregulated under UV-B radiation. We also performed a weighted gene co-expression network analysis (WGCNA) to explore the relationship among genes involved in plant hormone signal transduction, encoding transcription factors or participating in flavonoid biosynthesis. The transcription factors VcMYBPA1, MYBPA2.1, MYB114, MYBA2, MYBF, and MYB102 are likely activators, whereas MYB20, VcMYB14, MYB44, and VcMYB4a are inhibitors of the flavonoid biosynthetic pathway, as evidenced by the direction of correlation between the expression of these MYBs and flavonoid biosynthesis-related genes. The transcription factors bHLH74 and bHLH25 might interact with MYB repressors or directly inhibited the expression of flavonoid biosynthetic genes to control flavonoid accumulation. We also observed the downregulation of several genes belonging to the auxin, gibberellin and brassinosteroid biosynthetic pathways, suggesting that MYB inhibitors or activators are directly or indirectly regulated to promote flavonoid biosynthesis under UV-B radiation.

All-vacuum fabrication of yellow perovskite light-emitting diodes.

Yellow light-emitting diodes (LEDs) are widely utilized in high-quality lighting, light communication, indicator lamps, etc. Owing to their outstanding material properties and device performance, the metal halide perovskites have demonstrated a significant potential for LED applications. However, the performance of the yellow perovskite LEDs (PeLEDs) is inferior to that of their green and red counterparts, with the maximum external quantum efficiency (EQE) limited to ∼3.1%. Further, a majority of the yellow PeLEDs are fabricated using the spin-coating methods. The current study reports the development of the yellow CsPbBr2I PeLEDs based on an all-vacuum deposition approach, which has been widely employed in the commercial organic LEDs (OLEDs). By controlling the co-evaporation rate of CsI and PbBr2, the growth kinetics of the perovskite layer are regulated to achieve a small grain size of ∼31.8 nm. Consequently, an improved radiative recombination rate (8.04 × 10-9 cm3/s) is obtained owing to the spatial confinement effect. The PeLEDs based on the optimal perovskite film demonstrate the yellow electroluminescence (574 nm) with a maximum EQE of ∼3.7% and luminance of ∼16,200 cd/m2, thus, representing one of the most efficient and bright yellow PeLEDs. Overall, this study provides a useful guideline for realizing the efficient PeLEDs based on the thermal evaporation strategy and highlights the potential of PeLED as an efficient and bright yellow light source.

Spectra stable deep-blue light-emitting diodes based on cryolite-like cerium(III) halides with nanosecond d-f emission.

Next-generation wide color gamut displays require the development of efficient and toxic-free light-emitting materials meeting the crucial Rec. 2020 standard. With the rapid progress of green and red perovskite light-emitting diodes (PeLEDs), blue PeLEDs remain a central challenge because of the undesirable color coordinates and poor spectra stability. Here, we report Cs3CeBrxI6-x (x = 0 to 6) with the cryolite-like structure and stable and tunable color coordinates from (0.17, 0.02) to (0.15, 0.04). Further encouraged by the short exciton lifetime (26.1 ns) and high photoluminescence quantum yield (~76%), we construct Cs3CeBrxI6-x-based rare-earth LEDs via thermal evaporation. A seed layer strategy is conducted to improve the device's performance. The optimal Cs3CeI6 device achieves a maximum external quantum efficiency of 3.5% and a luminance of 470 cd m-2 with stable deep-blue color coordinates of (0.15, 0.04). Our work opens another avenue to achieving efficient and spectrally stable deep-blue LEDs.

Conservation and Diversity of miR166 Family Members From Highbush Blueberry (Vaccinium corymbosum) and Their Potential Functions in Abiotic Stress.

MicroRNA166 (miR166) is highly conserved and has diverse functions across plant species. The highbush blueberry (Vaccinium corymbosum) genome is thought to harbor 10 miRNA166 loci (Vco-miR166), but the extent of their evolutionary conservation or functional diversification remains unknown. In this study, we identified six additional Vco-miR166 loci based on conserved features of the miR166 family. Phylogenetic analyses showed that mature Vco-miR166s and their precursor cluster in several clades are evolutionary conserved with diverse species. The cis-regulatory elements in the Vco-miR166 promoters indicated functions related to different phytohormones and defense responses. We also identified putative targets of vco-miR166s, which targeted the same gene families, suggesting the functional conservation and diversification of Vco-miR166 family members. Furthermore, we examined the accumulation patterns of six mature Vco-miR166s in response to abiotic stresses by stem-loop reverse RT-qPCR, which revealed their upregulation under freezing, cold, and heat stress, while they were downregulated by drought compared to control growth conditions. However, Vco-miR166 members showed different expression patterns when exposed to salt stress. These results showed that conserved Vco-miR166 family members display functional diversification but also coordinately influence plant responses to abiotic stress.

Light Emission of Self-Trapped Excitons in Inorganic Metal Halides for Optoelectronic Applications.

Self-trapped excitons (STEs) have recently attracted tremendous interest due to their broadband emission, high photoluminescence quantum yield, and self-absorption-free properties, which enable a large range of optoelectronic applications such as lighting, displays, radiation detection, and special sensors. Unlike free excitons, the formation of STEs requires strong coupling between excited state excitons and the soft lattice in low electronic dimensional materials. The chemical and structural diversity of metal halides provides an ideal platform for developing efficient STE emission materials. Herein, an overview of recent progress on STE emission materials for optoelectronic applications is presented. The relationships between the fundamental emission mechanisms, chemical compositions, and device performances are systematically reviewed. On this basis, currently existing challenges and possible development opportunities in this field are presented.

Tomato BZR/BES transcription factor SlBZR1 positively regulates BR signaling and salt stress tolerance in tomato and Arabidopsis.

Brassinosteroids (BRs) play critical roles in plant growth and development, as well as in responses to abiotic stresses. The BRASSINAZOLE RESISTANT 1 (BZR1) and BRI1-EMS-SUPPRESSOR 1 (BES1) families of transcription factors have been elucidated largely in Arabidopsis and rice but not in other plant species. Here, we studied the functional characterization of a tomato (Solanum lycopersicum) BZR homolog gene, SlBZR1, in BR-regulated plant growth and tolerance to salt stress. SlBZR1 was highly expressed in the flowers and developing fruits of tomato. Both SlBZR1 and SlBZR1D (proline to leucine mutation at the 239th amino acid of SlBZR1) were transcriptional repressors and localized in the nucleus. SlBZR1 or SlBZR1D could interact with SlMYB30, SlMYBL2, SlPIF4, SlHAT1, SlIWS1 and SlREF6 in tomato. Overexpression of SlBZR1D enhanced the BR response and improved tolerance to salt stress in Arabidopsis, consistent with the phenotype of the Arabidopsis bes1-D mutant. Moreover, SlBZR1D-overexpressing tomato lines showed a short plant height, smaller and curly leaves, and delayed flowering. Additionally, SlBZR1D positively regulated salt tolerance in tomato and upregulated the expression of multiple stress-related genes. Our study provides new insights for understanding the function and mechanism of BZR transcription factors in BR-regulated plant growth and abiotic stress responses.

VcMYB4a, an R2R3-MYB transcription factor from Vaccinium corymbosum, negatively regulates salt, drought, and temperature stress.

MYB transcription factors (TFs) play important roles in the plant's response to abiotic stress. In this study, we cloned a novel MYB TF gene from Vaccinium corymbosum (blueberry) using rapid amplification of cDNA ends (RACE). The cDNA contained a 798-bp open reading frame that encodes a 265-amino acid protein. VcMYB4a possessed a C2/EAR-repressor motif domain and phylogenetic analysis showed that it clustered into a subgroup 4 with six Arabidopsis thaliana MYBs. Quantitative RT-PCR analysis demonstrated that VcMYB4a expression was downregulated by salt, drought, and cold treatment, but was induced by freezing and heat. Overexpression of VcMYB4a in blueberry callus enhanced sensitivity to salt, drought, cold, freezing, and heat stress. These results indicate that VcMYB4a may be an important repressor of abiotic stress in blueberry.

Ultrahigh-performance transparent conductive films of carbon-welded isolated single-wall carbon nanotubes.

Single-wall carbon nanotubes (SWCNTs) are ideal for fabricating transparent conductive films because of their small diameter, good optical and electrical properties, and excellent flexibility. However, a high intertube Schottky junction resistance, together with the existence of aggregated bundles of SWCNTs, leads to a degraded optoelectronic performance of the films. We report a network of isolated SWCNTs prepared by an injection floating catalyst chemical vapor deposition method, in which crossed SWCNTs are welded together by graphitic carbon. Pristine SWCNT films show a record low sheet resistance of 41 ohm □-1 at 90% transmittance for 550-nm light. After HNO3 treatment, the sheet resistance further decreases to 25 ohm □-1. Organic light-emitting diodes using this SWCNT film as anodes demonstrate a low turn-on voltage of 2.5 V, a high current efficiency of 75 cd A-1, and excellent flexibility. Investigation of isolated SWCNT-based field-effect transistors shows that the carbon-welded joints convert the Schottky contacts between metallic and semiconducting SWCNTs into near-ohmic ones, which significantly improves the conductivity of the transparent SWCNT network. Our work provides a new avenue of assembling individual SWCNTs into macroscopic thin films, which demonstrate great potential for use as transparent electrodes in various flexible electronics.

Hybrid host materials for highly efficient electrophosphorescence and thermally activated delayed fluorescence independent of the linkage mode.

Three non-conjugated hybrid host materials, tBu-OXD-o-L-TPA, tBu-OXD-m-L-TPA, and tBu-OXD-p-L-TPA, have been synthesized and characterized for their thermal, electrochemical, fluorescence, phosphorescence, and electroluminescence properties. Due to the non-conjugated spacer, the three hosts have a similar ET value as high as 2.71 eV, which is sufficiently high for blue phosphorescent and thermally activated delayed fluorescent (TADF) emitters. Different from the hosts with a direct linkage between a donor and an acceptor showing significantly distinct properties depending on linkage modes, the three new hosts demonstrate similar photophysical, electrochemical, and organic light-emitting device performances. Both phosphorescent and TADF devices with high efficiencies have been realized using all the three hosts. These results reveal a new merit of employing a non-conjugated spacer, which enables the synthesized hosts to show properties independent of the linkage mode. This might facilitate choosing materials with an economical synthesis process while not influencing their properties and thus enhance the potential of universal host materials.

Organic semiconductor heterojunctions: electrode-independent charge injectors for high-performance organic light-emitting diodes.

Organic light-emitting diodes (OLEDs) are driven by injected charges from an anode and a cathode. The low and high work function metals are necessary for the effective injection of electrons and holes, respectively. Here, we introduce a fully novel design concept using organic semiconductor heterojunctions (OSHJs) as the charge injectors for achieving highly efficient OLEDs, regardless of the work functions of the electrodes. In contrast to traditional injected charges from the electrodes, the injected charges originate from the OSHJs. The device performance was shown to be significantly improved in efficiency and stability compared to conventional OLEDs. Attractively, the OLEDs based on OSHJs as charge injectors still exhibited an impressive performance when the low work function Al was replaced by air- and chemistry-stable high work function metals, such as Au, Ag, and Cu, as the cathode contact, which has been suggested to be difficult in conventional OLEDs. This concept challenges the conventional design approach for the injection of charges and allows for the realization of practical applications of OLEDs with respect to high efficiency, selectable electrodes, and a long lifetime.