Transcription Factor McHB7 Improves Ice Plant Drought Tolerance through ABA Signaling Pathway.

As global climate change continues, drought episodes have become increasingly frequent. Studying plant stress tolerance is urgently needed to ensure food security. The common ice plant is one of the model halophyte plants for plant stress biology research. This study aimed to investigate the functions of a newly discovered transcription factor, Homeobox 7 (HB7), from the ice plant in response to drought stress. An efficient Agrobacterium-mediated transformation method was established in the ice plant, where ectopic McHB7 expression may be sustained for four weeks. The McHB7 overexpression (OE) plants displayed drought tolerance, and the activities of redox enzymes and chlorophyll content in the OE plants were higher than the wild type. Quantitative proteomics revealed 1910 and 495 proteins significantly changed in the OE leaves compared to the wild type under the control and drought conditions, respectively. Most increased proteins were involved in the tricarboxylic acid cycle, photosynthesis, glycolysis, pyruvate metabolism, and oxidative phosphorylation pathways. Some were found to participate in abscisic acid signaling or response. Furthermore, the abscisic acid levels increased in the OE compared with the wild type. McHB7 was revealed to bind to the promoter motifs of Early Responsive to Dehydration genes and abscisic acid-responsive genes, and protein-protein interaction analysis revealed candidate proteins responsive to stresses and hormones (e.g., abscisic acid). To conclude, McHB7 may contribute to enhance plant drought tolerance through abscisic acid signaling.

Functional analysis of PagNAC045 transcription factor that improves salt and ABA tolerance in transgenic tobacco.

BACKGROUND: Salt stress causes inhibition of plant growth and development, and always leads to an increasing threat to plant agriculture. Transcription factors regulate the expression of various genes for stress response and adaptation. It's crucial to reveal the regulatory mechanisms of transcription factors in the response to salt stress. RESULTS: A salt-inducible NAC transcription factor gene PagNAC045 was isolated from Populus alba×P. glandulosa. The PagNAC045 had a high sequence similarity with NAC045 (Potri.007G099400.1) in P. trichocarpa, and they both contained the same conserved motifs 1 and 2, which constitute the highly conserved NAM domain at the N-terminus. Protein-protein interaction (PPI) prediction showed that PagNAC045 potentially interacts with many proteins involved in plant hormone signaling, DNA-binding and transcriptional regulation. The results of subcellular localization and transient expression in tobacco leaves confirmed the nuclear localization of PagNAC045. Yeast two-hybrid revealed that PagNAC045 protein exhibits transcriptional activation property and the activation domain located in its C-terminus. In addition, the 1063 bp promoter of PagNAC045 was able to drive GUS gene expression in the leaves and roots. In poplar leaves and roots, PagNAC045 expression increased significantly by salt and ABA treatments. Tobacco seedlings overexpressing PagNAC045 exhibited enhanced tolerance to NaCl and ABA compared to the wild-type (WT). Yeast one-hybrid assay demonstrated that a bHLH104-like transcription factor can bind to the promoter sequence of PagNAC045. CONCLUSION: The PagNAC045 functions as positive regulator in plant responses to NaCl and ABA-mediated stresses.

Overexpression of McHB7 Transcription Factor from Mesembryanthemum crystallinum Improves Plant Salt Tolerance.

Mesembryanthemum crystallinum (common ice plant) is one of the facultative halophyte plants, and it serves as a model for investigating the molecular mechanisms underlying its salt stress response and tolerance. Here we cloned one of the homeobox transcription factor (TF) genes, McHB7, from the ice plant, which has 60% similarity with the Arabidopsis AtHB7. Overexpression of the McHB7 in Arabidopsis (OE) showed that the plants had significantly elevated relative water content (RWC), chlorophyll content, superoxide dismutase (SOD), and peroxidase (POD) activities after salt stress treatment. Our proteomic analysis identified 145 proteins to be significantly changed in abundance, and 66 were exclusively increased in the OE plants compared to the wild type (WT). After salt treatment, 979 and 959 metabolites were significantly increased and decreased, respectively, in the OE plants compared to the WT. The results demonstrate that the McHB7 can improve photosynthesis, increase the leaf chlorophyll content, and affect the TCA cycle by regulating metabolites (e.g., pyruvate) and proteins (e.g., citrate synthase). Moreover, McHB7 modulates the expression of stress-related proteins (e.g., superoxide dismutase, dehydroascorbate reductase, and pyrroline-5-carboxylate synthase B) to scavenge reactive oxygen species and enhance plant salt tolerance.

Overexpression of PagERF072 from Poplar Improves Salt Tolerance.

Extreme environments, especially drought and high salt conditions, seriously affect plant growth and development. Ethylene-responsive factor (ERF) transcription factors play an important role in salt stress response. In this study, a significantly upregulated ERF gene was identified in 84K (Populus alba × P. glandulosa), which was named PagERF072. PagERF072 was confirmed to be a nuclear-localized protein. The results of yeast two-hybrid (Y2H) assay showed that PagERF072 protein exhibited no self-activating activity, and yeast one-hybrid (Y1H) demonstrated that PagERF072 could specifically bind to GCC-box element. Under salt stress, the transgenic poplar lines overexpressing PagERF072 showed improved salt tolerance. The activities of peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) in transgenic poplars were significantly increased relative to those of wild-type (WT) plants, whereas malondialdehyde (MDA) content showed an opposite trend. In addition, reactive oxygen species (ROS) was significantly reduced, and the expression levels of POD- and SOD-related genes were significantly increased in transgenic poplars under salt stress compared with WT. All results indicate that overexpression of the PagERF072 gene can improve the salt tolerance of transgenic poplars.

Genome-Wide Identification and Expression Patterns of the F-box Family in Poplar under Salt Stress.

The F-box family exists in a wide variety of plants and plays an extremely important role in plant growth, development and stress responses. However, systematic studies of F-box family have not been reported in populus trichocarpa. In the present study, 245 PtrFBX proteins in total were identified, and a phylogenetic tree was constructed on the basis of their C-terminal conserved domains, which was divided into 16 groups (A-P). F-box proteins were located in 19 chromosomes and six scaffolds, and segmental duplication was main force for the evolution of the F-box family in poplar. Collinearity analysis was conducted between poplar and other species including Arabidopsis thaliana, Glycine max, Anemone vitifolia Buch, Oryza sativa and Zea mays, which indicated that poplar has a relatively close relationship with G. max. The promoter regions of PtrFBX genes mainly contain two kinds of cis-elements, including hormone-responsive elements and stress-related elements. Transcriptome analysis indicated that there were 82 differentially expressed PtrFBX genes (DEGs), among which 64 DEGs were in the roots, 17 in the leaves and 26 in the stems. In addition, a co-expression network analysis of four representative PtrFBX genes indicated that their co-expression gene sets were mainly involved in abiotic stress responses and complex physiological processes. Using bioinformatic methods, we explored the structure, evolution and expression pattern of F-box genes in poplar, which provided clues to the molecular function of F-box family members and the screening of salt-tolerant PtrFBX genes.

Genome-wide identification and expression analysis of the xyloglucan endotransglucosylase/hydrolase gene family in poplar.

BACKGROUND: Xyloglucan endotransglucosylase/hydrolase (XTH) family plays an important role in cell wall reconstruction and stress resistance in plants. However, the detailed characteristics of XTH family genes and their expression pattern under salt stress have not been reported in poplar. RESULTS: In this study, a total of 43 PtrXTH genes were identified from Populus simonii × Populus nigra, and most of them contain two conserved structures (Glyco_hydro_16 and XET_C domain). The promoters of the PtrXTH genes contain mutiple cis-acting elements related to growth and development and stress responses. Collinearity analysis revealed that the XTH genes from poplar has an evolutionary relationship with other six species, including Eucalyptus robusta, Solanum lycopersicum, Glycine max, Arabidopsis, Zea mays and Oryza sativa. Based on RNA-Seq analysis, the PtrXTH genes have different expression patterns in the roots, stems and leaves, and many of them are highly expressed in the roots. In addition, there are11 differentially expressed PtrXTH genes in the roots, 9 in the stems, and 7 in the leaves under salt stress. In addition, the accuracy of RNA-Seq results was verified by RT-qPCR. CONCLUSION: All the results indicated that XTH family genes may play an important role in tissue specificity and salt stress response. This study will lay a theoretical foundation for further study on molecular function of XTH genes in poplar.

Genome-wide analysis and expression profile of the bZIP gene family in poplar.

BACKGROUND: The bZIP gene family, which is widely present in plants, participates in varied biological processes including growth and development and stress responses. How do the genes regulate such biological processes? Systems biology is powerful for mechanistic understanding of gene functions. However, such studies have not yet been reported in poplar. RESULTS: In this study, we identified 86 poplar bZIP transcription factors and described their conserved domains. According to the results of phylogenetic tree, we divided these members into 12 groups with specific gene structures and motif compositions. The corresponding genes that harbor a large number of segmental duplication events are unevenly distributed on the 17 poplar chromosomes. In addition, we further examined collinearity between these genes and the related genes from six other species. Evidence from transcriptomic data indicated that the bZIP genes in poplar displayed different expression patterns in roots, stems, and leaves. Furthermore, we identified 45 bZIP genes that respond to salt stress in the three tissues. We performed co-expression analysis on the representative genes, followed by gene set enrichment analysis. The results demonstrated that tissue differentially expressed genes, especially the co-expressing genes, are mainly involved in secondary metabolic and secondary metabolite biosynthetic processes. However, salt stress responsive genes and their co-expressing genes mainly participate in the regulation of metal ion transport, and methionine biosynthetic. CONCLUSIONS: Using comparative genomics and systems biology approaches, we, for the first time, systematically explore the structures and functions of the bZIP gene family in poplar. It appears that the bZIP gene family plays significant roles in regulation of poplar development and growth and salt stress responses through differential gene networks or biological processes. These findings provide the foundation for genetic breeding by engineering target regulators and corresponding gene networks into poplar lines.

Genome-wide search and structural and functional analyses for late embryogenesis-abundant (LEA) gene family in poplar.

BACKGROUND: The Late Embryogenesis-Abundant (LEA) gene families, which play significant roles in regulation of tolerance to abiotic stresses, widely exist in higher plants. Poplar is a tree species that has important ecological and economic values. But systematic studies on the gene family have not been reported yet in poplar. RESULTS: On the basis of genome-wide search, we identified 88 LEA genes from Populus trichocarpa and renamed them as PtrLEA. The PtrLEA genes have fewer introns, and their promoters contain more cis-regulatory elements related to abiotic stress tolerance. Our results from comparative genomics indicated that the PtrLEA genes are conserved and homologous to related genes in other species, such as Eucalyptus robusta, Solanum lycopersicum and Arabidopsis. Using RNA-Seq data collected from poplar under two conditions (with and without salt treatment), we detected 24, 22 and 19 differentially expressed genes (DEGs) in roots, stems and leaves, respectively. Then we performed spatiotemporal expression analysis of the four up-regulated DEGs shared by the tissues, constructed gene co-expression-based networks, and investigated gene function annotations. CONCLUSION: Lines of evidence indicated that the PtrLEA genes play significant roles in poplar growth and development, as well as in responses to salt stress.

Functional Characterization of PsnNAC036 under Salinity and High Temperature Stresses.

Plant growth and development are challenged by biotic and abiotic stresses including salinity and heat stresses. For Populus simonii × P. nigra as an important greening and economic tree species in China, increasing soil salinization and global warming have become major environmental challenges. We aim to unravel the molecular mechanisms underlying tree tolerance to salt stress and high temprerature (HT) stress conditions. Transcriptomics revealed that a PsnNAC036 transcription factor (TF) was significantly induced by salt stress in P. simonii × P. nigra. This study focuses on addressing the biological functions of PsnNAC036. The gene was cloned, and its temporal and spatial expression was analyzed under different stresses. PsnNAC036 was significantly upregulated under 150 mM NaCl and 37 °C for 12 h. The result is consistent with the presence of stress responsive cis-elements in the PsnNAC036 promoter. Subcellular localization analysis showed that PsnNAC036 was targeted to the nucleus. Additionally, PsnNAC036 was highly expressed in the leaves and roots. To investigate the core activation region of PsnNAC036 protein and its potential regulatory factors and targets, we conducted trans-activation analysis and the result indicates that the C-terminal region of 191-343 amino acids of the PsnNAC036 was a potent activation domain. Furthermore, overexpression of PsnNAC036 stimulated plant growth and enhanced salinity and HT tolerance. Moreover, 14 stress-related genes upregulated in the transgenic plants under high salt and HT conditions may be potential targets of the PsnNAC036. All the results demonstrate that PsnNAC036 plays an important role in salt and HT stress tolerance.

Amplification Strategy of Silver Nanoclusters with a Satellite-Nanostructure for Substrate-Free Assay of Alkaline Phosphatase by ICP-MS.

Alkaline phosphatase (ALP) plays critical roles in signal transmission and cell growth/apoptosis. Its abnormal level in serum/cell is tightly related to diseases, thus, serum and cellular ALP detection is of great significance for disease diagnosis. Herein, a novel approach for ALP assay based on a satellite-nanostructure is developed by conjugating lanthanide upconversion nanoparticles (UCNPs) with silver nanoclusters (AgNCs) through DNA bridging. UCNPs serve as the cores to conjugate with DNA fragments, followed by assembly of AgNCs as the satellites on UCNPs surface through the AgNCs-cytosine affinity, to produce the satellite-nanostructure of UCNPs@DNA-AgNCs. The presence of ALP converts phosphate groups into hydroxyl groups at DNA helix, weakening the coordination of DNA with UCNPs. As a result, the satellite AgNC labeling on DNA fragments strips off the UCNP surface. Silver is quantified by measuring isotope 107Ag with ICP-MS, which further derives the content of ALP by correlation to the number of AgNCs. A linear calibration range is obtained in 0.005-120 U/L with a detection limit of 1.8 mU/L. The distinct advantage of this strategy, on one hand, is the substrate-free feature that eliminates the intermediate process of substrate reaction, where the substrate activity decrease and its instability may significantly deteriorate the sensitivity. On the other hand, ALP triggers the production of a large number of AgNCs resulting in substantial amplification on ICP-MS signal to give a favorable sensitivity. This is the first attempt for ALP detection by inductively coupled plasma mass spectrometry.

Ectopic expression of a poplar gene NAC13 confers enhanced tolerance to salinity stress in transgenic Nicotiana tabacum.

NACs are one of the major transcription factor families in plants which play an important role in plant growth and development, as well as in adverse stress responses. In this study, we cloned a salt-inducible NAC transcription factor gene (NAC13) from a poplar variety 84K, followed by transforming it into both Nicotiana tabacum and Arabidopsis thaliana. Stable expression analysis of 35S::NAC13-GFP fusion protein in Arabidopsis indicated that NAC13 protein was localized to the nucleus. We also obtained five transgenic tobacco lines. Evidence from morphological and physiological characterization and salt treatment analyses indicated that in the transgenic tobacco the salt tolerance was enhanced, suggesting that NAC13 gene may function as a positive regulator in tobacco responses to salt stress.

Placeholder Strategy with Upconversion Nanoparticles-Eriochrome Black T Conjugate for a Colorimetric Assay of an Anthrax Biomarker.

The timely warning of the germination of bacterial spores and their prevention are highly important to minimize their potential detrimental effects and for disease control. Thus, a sensitive and selective assay of biomarkers is most desirable. In this work, a nanoprobe is constructed by conjugating lanthanide upconversion nanoparticles (UCNPs) with sodium tripolyphosphate (TPP) and eriochrome black T (EBT). The nanoprobe, UCNPs-TPP/EBT, serves as a platform for the detection of the anthrax biomarker, dipicolinic acid (DPA). In principle, DPA displaces EBT from the UCNPs-TPP/EBT nanoconjugate, resulting in a color change from magenta to blue because of the release of free EBT into the aqueous solution. The binding sites on UCNPs are partly preblocked with TPP as the placeholder molecule, leaving a desired number of binding sites for EBT conjugation. On the basis of this dye displacement reaction, a novel colorimetric assay protocol for DPA is developed, deriving a linear calibration range from 2 to 200 µM with a detection limit of 0.9 µM, which is well below the infectious dose of the spores (60 µM). The assay platform exhibits excellent anti-interference capability when treating a real biological sample matrix. The present method is validated by the analysis of DPA in human serum, and its practical application is further demonstrated by monitoring the DPA release upon spore germination.

Highly Sensitive Detection of MicroRNA-21 with ICPMS via Hybridization Accumulation of Upconversion Nanoparticles.

A highly sensitive platform is developed for the determination of microRNA-21 (miRNA-21) with inductively coupled plasma mass spectrometry (ICPMS). It includes the following operations: Hairpin structures DNA H1 and H2 are designed, and DNA H1 is bound to ultrasmall lanthanide upconversion nanoparticles (UCNPs) to produce UCNPs@DNA conjugate probes. Target miRNA triggers a chain reaction for alternating hybridization between DNA H1 (bound on UCNPs@DNA probe) and DNA H2. This leads to UCNPs accumulation and serves as an efficient amplification strategy for UCNPs. The concentration of miRNA-21 is closely correlated to the number of UCNPs; thus, the detection of 89Y by ICPMS provides a promising approach for miRNA quantification. This protocol exhibits high sensitivity to miRNA-21 within 0.1-500 fM, along with a detection limit of 41 aM, which is among the hitherto reported most sensitive procedures. It is worth mentioning that rare earth elements are scarcely present in living systems, which minimizes the background for ICPMS detection and excludes potential interferences from the coexisting species, which is most suited for biological assay.

DB-DCAFN: dual-branch deformable cross-attention fusion network for bacterial segmentation.

Sputum smear tests are critical for the diagnosis of respiratory diseases. Automatic segmentation of bacteria from sputum smear images is important for improving diagnostic efficiency. However, this remains a challenging task owing to the high interclass similarity among different categories of bacteria and the low contrast of the bacterial edges. To explore more levels of global pattern features to promote the distinguishing ability of bacterial categories and maintain sufficient local fine-grained features to ensure accurate localization of ambiguous bacteria simultaneously, we propose a novel dual-branch deformable cross-attention fusion network (DB-DCAFN) for accurate bacterial segmentation. Specifically, we first designed a dual-branch encoder consisting of multiple convolution and transformer blocks in parallel to simultaneously extract multilevel local and global features. We then designed a sparse and deformable cross-attention module to capture the semantic dependencies between local and global features, which can bridge the semantic gap and fuse features effectively. Furthermore, we designed a feature assignment fusion module to enhance meaningful features using an adaptive feature weighting strategy to obtain more accurate segmentation. We conducted extensive experiments to evaluate the effectiveness of DB-DCAFN on a clinical dataset comprising three bacterial categories: Acinetobacter baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa. The experimental results demonstrate that the proposed DB-DCAFN outperforms other state-of-the-art methods and is effective at segmenting bacteria from sputum smear images.

Eu-Doped MOF-based high-efficiency fluorescent sensor for detecting 2,4-dinitrophenol and 2,4,6-trinitrophenol simultaneously.

Nitroaromatic explosives pose a great threat to the environment and human safety. It is very important to design simple, highly efficient and multifunctional sensors for detecting nitroaromatic explosives. However, a few sensors can determine multicomponent nitroaromatic explosives simultaneously. Eu functionalized MOF-253 (Eu@MOF-253) hybrid material was synthesized using the post-synthetic modification method. The introduction of Eu3+ in MOF-253 caused the fluorescence peak of the ligand to show a distinct red-shift due to its polarization enhancement effect in the presence of 2,4-DNP. The emission and excitation spectra of the Eu@MOF-253 sensor showed overlap with the ultraviolet-visible (UV-vis) absorption spectra of the representative nitroaromatic explosives 2,4-dinitrophenol (2,4-DNP) and 2,4,6-trinitrophenol (TNP). Therefore, it is feasible to discriminate and quantify TNP and 2,4-DNP simultaneously. As proposed, the Eu@MOF-253 luminescent sensor was highly sensitive and selective towards TNP and 2,4-DNP. The other coexisting nitroaromatic explosives did not interfere with the determination. Upon addition of TNP, the fluorescence of the Eu@MOF-253 sensor decreased dramatically and showed an excellent quenching constant (Ksv) of 1.58 × 106. The fluorescence intensities of the Eu@MOF-253 sensor presented good linear relationships with concentrations of TNP and 2,4-DNP ranging from 0.01-100 µM and 0.01-25 µM, respectively. Low limits of detection (LOD) for both 2,4-DNP and TNP were approximately 10 nM. The determination mechanism is mainly ascribed to the internal filtration effect (IFE) and electron transfer. This work provides a practical method for the highly efficient determination of nitroaromatic explosives.

Genome-wide analysis of poplar HD-Zip family and over-expression of PsnHDZ63 confers salt tolerance in transgenic Populus simonii × P.nigra.

HD-Zip is a plant-specific HB transcription factor, which participates in plant development and stress response. In this study, we identified 63 poplar HD-Zip transcription factors, which were randomly distributed on 19 chromosomes of poplar. Based on the gene structure and phylogenetic relationship, these members are divided into four groups, which have a variety of collinear evolutionary relationships. They also have rich segmental replication events and experienced strong purification selection. Based on RNA-seq analysis, we profiled the expression pattern of the 63 HD-Zip members under salt stress. Subsequently, we carried out in-depth study on the significantly up-regulated PsnHDZ63 in the stems and leaves. The transgenic Populus simonii × P.nigra plants over-expressing PsnHDZ63 displayed better morphological and physiological indexes than WT under salt stress. In addition, PsnHDZ63 enhanced salt stress tolerance of transgenic lines by combining effective stress-resistant elements to improve reactive oxygen species scavenging ability. These studies laid a foundation for a comprehensive understanding of poplar HD-Zip family members, and revealed the important role of PsnHDZ63 in plant salt tolerance.

Characterization of the Poplar R2R3-MYB Gene Family and Over-Expression of PsnMYB108 Confers Salt Tolerance in Transgenic Tobacco.

The MYB, one of the largest transcription factor families in plants, is related to various biological processes. For an example, the R2R3-MYB family plays an important role in regulation of primary and secondary metabolism, plant growth and development, and responses to hormones and stresses. However, functional studies on the poplar R2R3-MYB genes are limited. In this study, we identified 207 poplar R2R3-MYB genes that are unevenly distributed on the 19 chromosomes of poplar, followed by characterization of their conserved domains. On the basis of phylogenetic analysis, these genes can be divided into 23 groups. Evidence from synteny analyses indicated that the poplar R2R3-MYB gene family is featured by tandem and segmental duplication events. On the basis of RNA-Seq data, we investigated salt responsive genes and explored their expression patterns. Furthermore, we cloned the PsnMYB108 gene from poplar, which is significantly up-regulated in roots and leaves in response to salt stress. To validate its function, we developed transgenic tobacco plants that over-express the PsnMYB108 gene. It appears that the transgenic lines are more tolerant to salt stress than the wild type does. Evidence from physiological analyses demonstrated that over-expression of PsnMYB108 may improve tobacco salt stress tolerance by increasing the reactive oxygen species scavenging ability and the accumulation of proline. These results laid the foundation for future analysis and functional studies of poplar R2R3-MYB family members, and revealed that PsnMYB108 plays an important role in improving plant salt stress tolerance.

Hybrids of Upconversion Nanoparticles and Silver Nanoclusters Ensure Superior Bactericidal Capability via Combined Sterilization.

It is highly desired to develop new antibacterial agents with superior bactericidal efficiency for minimizing the damage to biological cells. We developed a combined antibacterial nanohybrid exhibiting a superb bactericidal effect and excellent biocompatibility by integrating upconversion nanoparticles (UCNPs) with silver nanoclusters (AgNCs). UCNPs and methylene blue (MB) molecules were encapsulated with silica microspheres via microemulsion, with MB as the photosensitizer. Silver ions (Ag+) were reduced by amino groups on the surface of silica spheres, wherein silver nanoclusters (AgNCs) were formed in situ to produce the nanohybrid, UCNPs@SiO2(MB)@AgNCs. UCNPs emit visible light at 655 nm under excitation by near-infrared radiation (NIR, 980 nm). MB absorbs the emission from UCNPs to generate toxic singlet oxygen (1O2), which leads to the apoptosis of bacteria cells. Meanwhile, silver ions released from AgNCs destroy the bacteria membrane structure. Upon NIR irradiation at 980 nm for 10 min, 8.33 µg mL-1 nanohybrid results in a 100% killing rate for both Gram-positive S. aureus (+) and Gram-negative E. coli (-).

Comprehensive analysis of the three-amino-acid-loop-extension gene family and its tissue-differential expression in response to salt stress in poplar.

The three-amino-acid-loop-extension (TALE) transcription factor gene family is widely present in plants and plays an important role in its growth and development. However, studies on the gene family are limited in poplar. In this study, we investigated 35 TALE gene family members in terms of their evolutionary relationship, classification, physicochemical properties, gene structures, and protein motifs. We divided the genes into four classes, based on their protein sequences similarity. The members from each class share similar gene structures and motif compositions. Evidence from transcript profiling indicated that the majority of the TALE genes exhibited distinct expression patterns over leaf, stem, and root tissues. Out of the 35 genes, 17 genes are highly expressed in stems, suggesting that the TALE gene family may play an important role in secondary growth and wood formation. Furthermore, out of the 35 genes, 11 genes are responsive to salt stress, and the spatio-temporal expression patterns of these 11 genes under salt stress were analysed using RT-qPCR. Yeast two-hybridization analysis indicated that poplar TALE proteins from different classes can form heterodimers. These results lay the foundation for future studies on biological functions of poplar TALE genes.

Functional characterization of poplar NAC13 gene in salt tolerance.

Transcription factor (TF) genes play a critical role in plant abiotic and biotic stress responses. In this study, we cloned a poplar TF NAC13 gene (Potri.001G404100.1), which is significantly up-regulated to salt stress. Then we developed gene overexpression and antisense suppression constructions driven by CaMV35S, and successfully transferred them to a poplar variety 84 K (Populus alba × P. glandulosa), respectively. Evidence from molecular assay indicated that NAC13 overexpression and antisense suppression fragments have been integrated into the poplar genome. The morphological and physiological characterization and salt treatment results indicated the NAC13-overexpressing transgenic plants enhance salt tolerance significantly, compared to wide type. In contrast, the NAC13-suppressing transgenic plants are significantly sensitive to salt stress, compared to wide type. Evidence from transgenic Arabidopsis expressing GUS gene indicated that the gene driven by NAC13 promoter is mainly expressed in the roots and leaves of young plants. These studies indicate that the NAC13 gene plays a vital role in salt stress response.