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Article

Identification of the Populus euphratica XTHs Gene Family and the Response of PeXTH7 to Abiotic Stress

by
Jing Li
1,†,
Hongyan Jin
1,†,
Tongrui Song
1,
Donghui Miao
1,
Qi Ning
1,
Jianhao Sun
1,
Zhijun Li
1,
Peipei Jiao
1,* and
Zhihua Wu
2,*
1
Xinjiang Production and Construction Corps Key Laboratory of Protection and Utilization of Biological Resources in Tarim Basin, College of Life Science & Technology, Tarim University, Alar 843300, China
2
College of Life Sciences, Zhejiang Normal University, Jinhua 321004, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Plants 2025, 14(24), 3847; https://doi.org/10.3390/plants14243847
Submission received: 1 November 2025 / Revised: 13 December 2025 / Accepted: 14 December 2025 / Published: 17 December 2025
(This article belongs to the Special Issue Physiological and Molecular Mechanisms of Plant Resistance to Abiotic Stress)
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Abstract

Populus euphratica Oliv. serves as a keystone species in desert riparian ecosystems. Owing to its pronounced tolerance to drought and salinity, as well as its robust reproductive capacity, it has become a pioneer species in desert oases. The xyloglucan endotransglucosylase (XET)/hydrolase (XTH) gene family plays a critical role in the remodeling of plant cell walls; however, its potential biological functions in poplar remain poorly understood. In this study, we identified the XTH gene family in P. euphratica and conducted a preliminary functional analysis. A total of 33 PeXTH genes were identified, which were unevenly distributed across the chromosomes, with the highest density observed on chromosome 6. Conserved domain analysis indicated that most members contain the typical GH16 domain associated with xyloglucan endotransglucosylase activity. Phylogenetic analysis classified them into four distinct subgroups, exhibiting evolutionary conservation with the model dicot plant of Arabidopsis thaliana. Notably, the promoter analysis revealed an abundance of ABA-responsive and stress-related cis-elements, suggesting their potential involvement in response to multiple stresses. Under drought stress, PeXTH7 (PeuTF07G00088.1) exhibited a distinct expression pattern, with transcript levels significantly increasing with persistent treatment. RT-qPCR results confirmed that PeXTH7 is highly expressed in both roots and leaves. Furthermore, subcellular localization assays demonstrated that the PeXTH7 protein localizes to the secretory pathway and the cell wall, implying a role in cell wall dynamic remodeling through the regulation of xyloglucan metabolism. The PeXTH7-overexpressing transgenic lines exhibited a significant increase in root length compared to the wild-type controls. As the first systematic analysis of the XTH gene family in P. euphratica, this study fills an important knowledge gap and provides new insights into the adaptive mechanisms of desert tree species.

1. Introduction

Under the pressure of intensifying global climate change and worsening water scarcity, drought stress has emerged as a major environmental constraint on agricultural productivity [1]. In response, plants have evolved sophisticated adaptive mechanisms that allow them to perceive external stress signals and mount appropriate physiological and molecular responses [2]. Studies have shown that the cell wall acts as the primary interface for plant–environment interactions, detecting external changes and relaying stress signals to the plasma membrane. This signaling cascade leads to changes in cytosolic Ca2+, reactive oxygen species (ROS), and hormone levels—including abscisic acid (ABA)—and further modulates the synthesis and remodeling of cell wall components through regulation of related gene expression, thereby enhancing plant adaptation to abiotic stress [3]. As the first barrier between plant cells and the external environment, the cell wall plays essential roles not only in sensing and transducing abiotic stress signals and maintaining structural integrity, but also in supporting plant growth and development [4]. The primary cell wall consists mainly of cellulose microfibrils, hemicellulose, pectin, and glycoproteins, which form a complex hydrated network. Water deficit can alter the composition of the cell wall, affecting turgor pressure regulation and growth dynamics, thereby modulating plant growth. Under stress conditions, plants upregulate genes involved in cell wall polysaccharide synthesis and modification through mechanisms such as stress-induced Ca2+ signaling oscillations and ABA-dependent pathways, thus preserving cell wall integrity and improving stress adaptability [5].
Xyloglucan (XG) serves as the predominant hemicellulose in the primary cell walls of dicotyledons and non-graminaceous monocotyledons. Its backbone consists of a β-(1 → 4)-linked D-glucan chain, which interacts with cellulose microfibrils via hydrogen bonds to form a complex network crucial for maintaining cell wall mechanical strength. Research has shown that under various abiotic stress conditions, transcription of genes involved in the lignin biosynthesis pathway is significantly upregulated. This transcriptional activation is accompanied by enhanced lignin deposition, which reinforces cell wall rigidity—an adaptive response that contributes to improved plant stress tolerance [6].
Xyloglucan endotransglycosylase/hydrolase (XTH), a key enzyme belonging to the glycoside hydrolase family 16 (GH16), catalyzes the cleavage and re-ligation of xyloglucan chains within the cellulose framework and is widely recognized as a pivotal regulator of cell wall remodeling. Through its modulation of xyloglucan metabolism, XTH dynamically regulates cell wall loosening and reinforcement, thereby directly influencing cellular elongation and expansion. Substantial evidence has demonstrated that plant roots exhibit greater sensitivity to abiotic stresses compared to other organs [7]. Functioning as the primary site for environmental stress perception, root growth displays a strong correlation with XTH-mediated xyloglucan metabolic dynamics, which may account for their enhanced stress responsiveness. Experimental findings indicate that when xyloglucan content in the Golgi apparatus substantially exceeds XTH levels, XTH incorporates into the cell wall primarily as xyloglucan-XTH complexes, resulting in enhanced wall rigidity and suppressed cell elongation. Conversely, under conditions where XTH abundance surpasses xyloglucan availability, XTH enters the cell wall as free enzymes that facilitate xyloglucan hydrolysis and transglycosylation, leading to wall loosening and promoted cell elongation [8].
Populus euphratica is a forest-forming tree species native to arid desert regions, primarily distributed across saline-alkali wastelands, desert areas, and river alluvial plains in northwestern China. As a pioneer species in desert riparian ecosystems, its remarkable adaptability to arid and saline-alkali environments establishes P. euphratica as a key woody model for studying plant responses to abiotic stresses such as drought and salinity [9,10]. Studies have demonstrated that under drought stress, P. euphratica seedlings exhibit thickening of the taproot, increased lateral root density, and significant modifications in root system architecture; these morphological adjustments contribute to enhanced water uptake and reduced water loss [11,12]. Furthermore, the dynamic remodeling of root system architecture (RSA) enables plants to directionally grow toward favorable soil conditions while avoiding adverse environments, thereby significantly improving their survival capacity [13].
Preliminary studies suggest that XTH primarily localizes to and functions in the primary cell wall, where it participates in regulating root cap development and the expression of genes related to root cap formation. By modulating cell wall elasticity and extensibility, XTH plays a significant role in plant adaptation to adverse environmental conditions [14]. Currently, 33, 29, 41, and 71 members of the XTH gene family members have been identified in A.thaliana [15], Oryza sativa [16], Populus tomentosa [17], and wheat [18], respectively. Increased expression of XTH strengthens the connection between primary and secondary walls in mesophyll cells by reducing the length of xyloglucan, which helps plants adapt to high temperatures [19]. In addition, XTH genes are also involved in regulating plant growth and development. Five XTH genes (OfXTH24, 27, 32, 35, and 36) in Osmanthus fragrans respond to changes in environmental temperature and participate in the regulation of flowering [20]. Transcriptomic analysis of AcXTHs in Ananas comosus indicates that it involved in the regulation of fruit ripening and Crassulacean acid metabolism (CAM) and exhibit tissue specificity. Real-time fluorescent quantitative PCR analysis shows that AcXTH18 is involved in root growth of A. comosus [21]. Research has found that the SsXTH gene in Schima superba participates in glycoside metabolism through the transfer and hydrolysis of xyloglucan in the cell wall, thereby regulating the elongation of plant fibers [22]. During tomato fruit development, a novel XTH gene (SlXTH5) was identified with high expression in mature fruits, correlating with xyloglucan depolymerization [23]. Heterologous overexpression of the pepper CaXTH3 in A. thaliana induced severe leaf curling, implying its role in cell wall remodeling and reinforcement, which may help protect mesophyll cells under drought stress [24]. In sugar beet, XTH has been shown to undergo changes during abiotic stress responses and is involved in stomatal development and function by modulating the flexibility and integrity of guard cell walls [25]. These findings collectively provide a foundation for understanding plant stress regulation mechanisms mediated by cell wall signaling. In recent years, with the release of high-quality genomes and multi-omics data from Populus plants, it has become easier to identify and analyze the biological function of XTH gene family [26,27,28].
In summary, XTH genes are closely associated with multiple aspects of plant growth and development, including root elongation, leaf venation patterning, fruit maturation, and stomatal development. Accumulating evidence demonstrates that XTH plays a crucial role in plant responses to abiotic stress, offering important insights into cell wall signal-mediated stress regulatory pathways. However, the potential function of the XTH family in the desert tree species P. euphratica remains elusive. In order to fill this knowledge gap, we identified, analyzed and predicted the PeXTH family, and functionally characterized the drought-responsive member PeXTH7 to elucidate its role in root development and stress adaptation. Therefore, this study aims to identify and characterize the XTH gene family in poplar through genomic and bioinformatic analysis, with the objective of elucidating its potential functions in drought resistance. These results provide new insights for further understanding the role of PeXTH in response to abiotic stress, and also have important significance for the development and utilization of desert plant germplasm resources.

2. Results

2.1. Identification and Prediction of Physical and Chemical Properties of PeXTHs Family Members

A total of 33 PeXTH family members were identified in P. euphratica. The physicochemical properties of the encoded PeXTH proteins—including molecular weight (MW), amino acid number, instability index, theoretical isoelectric point (pI), grand average of hydropathicity (GRAVY), and subcellular localization—were analyzed using TBtools (version 2.119) and Expasy (https://web.expasy.org/protparam/; accessed on 24 November 2024). The results revealed that the molecular weights of PeXTH proteins range from 23.83 kDa to 39.49 kDa, with corresponding amino acid lengths varying between 210 and 338 residues. All members exhibit instability indices ranging from 55.81 to 71.41, indicating that they were generally unstable under in vitro conditions. The theoretical pI values vary widely from 4.48 to 9.58, likely reflecting differences in amino acid composition and polarity. Moreover, all GRAVY values were negative, confirming the overall hydrophilic nature of these proteins. Subcellular localization predictions suggest that 21 PeXTH proteins were localized to the cell wall, whereas the remaining 12 were predicted in both the cell wall and cytoplasm, implying potential roles in coordinating cell wall dynamics with intracellular signaling. Detailed physicochemical characteristics are provided in Table 1.

2.2. Analysis of Gene and Protein Structure of PeXTHs

The gene distribution of conserved domains in PeXTHs and gene exon and intron group map were completed using the GSDS (Gene Structure Display Server) online platform. The prediction and visualization of conserved protein motifs were achieved with the help of the MEME (Multiple Em for Motif Elicitation) website. Bioinformatics analysis showed that the amino acid sequences of the P. euphratica XTH gene family contained 10 different characteristic motifs, among which motifs 1–7 and motif 10 were highly conserved in most members, while motif 9 was only present in three genes and showed low conservation (Figure 1A). Conservative domain analysis further confirmed that this gene family contains three different characteristic functional domains, among which GH16-XET (Glycoside Hydrolase Family 16 Xyloglucan Endotransglucosylase) is the main pfam model. This result is consistent with the reported catalytic domain characteristics of xyloglucan endotransglucosylase/hydrogenase (XTH) (Figure 1B). Gene structure analysis revealed that the number of exons in each member does not exceed four (Figure 1C); this minimalistic exon-intron arrangement pattern may be related to their functional conservation. The identification of conserved protein domains of PeXTHs revealed the presence of ten conserved motifs (motifs 1–10; Figure 1D). These findings suggest that the core functional regions are evolutionarily conserved.

2.3. Prediction of Cis-Acting Elements in PeXTHs Promoter Region

The 2 kb promoter sequences upstream of the transcription start site (TSS) of all candidate genes were extracted, and cis-acting elements within these promoter regions were identified using online prediction tools. Systematic analysis revealed a total of 22 types of cis-regulatory elements, which were functionally categorized into four groups: abiotic/biotic stress-related, hormone-responsive, light-responsive, and growth/development-related elements. Among these, hormone-responsive elements were the most abundant, with nine types identified, including recognition sites for abscisic acid (ABA), methyl jasmonate (MeJA), gibberellin (GA), and salicylic acid (SA). ABA-responsive elements constituted the largest proportion within this category. Among the stress-related elements, hypoxia-responsive elements were predominant (Figure 2). These findings suggest that PeXTH genes may play diverse and important roles in regulating various physiological processes in P. euphratica, particularly under abiotic and biotic stress conditions. The presence of these cis-elements implies that the PeXTH gene family may be involved in modulating gene expression and multiple signaling pathways to enhance environmental stress adaptation.

2.4. Collinearity Analysis of XTHs Within P. euphratica and Among Multiple Species

By mapping the collinearity relationships among the 33 member genes within the P. euphratica gene family, 13 pairs of collinear PeXTHs genes were identified, including PeuTF05G01755.1, PeuTF02G00374.1, and PeuTF11G00627.1, each having two pairs of homologous genes, indicating that during the evolutionary process of P. euphratica, XTHs underwent multiple segmental duplications or repetitions, which facilitated the evolution and expansion of the gene family (Figure 3). Based on the collinearity relationships, 13 gene pairs were selected for selective pressure analysis, as shown in Table 2, with Ka/Ks values all less than 1, indicating that this gene family has been subjected to strong purifying selection pressure during evolution.
We performed interspecific collinearity analysis between P. euphratica and A. thaliana, as well as with Populus deltoides (a drought-tolerant poplar species of Salicaceae), Populus pruinosa (a drought-sensitive poplar species), and Salix sinopurpurea (a drought-sensitive willow species of Salicaceae). The analysis revealed 18 collinear gene pairs between P. euphratica and A. thaliana (Figure 4), whereas the numbers of collinear pairs between P. euphratica and P. deltoides, P. pruinosa, and S. sinopurpurea were 30, 28, and 29, respectively. These results indicate that the XTH gene family exhibits significantly higher evolutionary conservation within the Salicaceae family than across families (as represented by A. thaliana), suggesting that this gene family may have maintained greater structural stability through gene duplication and functional differentiation during adaptive evolution in woody plants.
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Figure 3. Intraspecific synteny analysis of 33 PeXTHs in P. euphratica. Green lines represent P. euphratica chromosomes, and gray lines indicate syntenic pairs of PeXTH fragment repeat genes.
Figure 3. Intraspecific synteny analysis of 33 PeXTHs in P. euphratica. Green lines represent P. euphratica chromosomes, and gray lines indicate syntenic pairs of PeXTH fragment repeat genes.
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Figure 4. XTH colinear analysis among multiple species. Colinear analysis of P. euphratica and four other species, A. thaliana, P. deltoides, P. pruinosa, and S. sinopurpurea. Gray lines indicate colinear segments between the P. euphratica genome and those of other species, while red lines indicate XTH colinear pairs among species.
Figure 4. XTH colinear analysis among multiple species. Colinear analysis of P. euphratica and four other species, A. thaliana, P. deltoides, P. pruinosa, and S. sinopurpurea. Gray lines indicate colinear segments between the P. euphratica genome and those of other species, while red lines indicate XTH colinear pairs among species.
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2.5. Chromosomal Localization Analysis of PeXTHs

Chromosomal localization analysis revealed that the 33 identified PeXTH genes are unevenly distributed across 16 chromosomes in P. euphratica (Figure 5). No family members were detected on chromosomes 12, 15, and 17. Gene distribution density varied among chromosomes, with chromosome 6 harboring the highest number (four PeXTH genes). Notably, two genes each were densely clustered on chromosomes 6, 11, and 19, suggesting potential hotspots for XTH gene localization in the P. euphratica genome. This genomic arrangement suggests that the proteins encoded by these genes may share functional similarities, reflecting potential evolutionary conservation within this gene family.

2.6. Phylogenetic Tree of PeXTHs

A phylogenetic tree was constructed using the ML (Maximum Likelihood) method based on protein sequences of 33 XTH genes from P. euphratica and homologous sequences from other species (Figure 6). Following the classification scheme established for AtXTHs, the 159 XTHs members from five species were categorized into four distinct groups: Group I/II, Group IIIA, Group IIIB, and the Ancestral Group. Members of Groups I, II, and IIIB exhibit xyloglucan endotransglucosylase (XET) activity, enabling cleavage and religation of xyloglucan chains, whereas Group IIIA members display xyloglucan endohydrolase (XEH) activity, specifically hydrolyzing β-1,4-glycosidic bonds within xyloglucan polymers. Among the PeXTHs, 23, 5, 4, and 1 members were assigned to these subgroups, respectively. Given that AtXTHs within the same subgroup often share functional similarities, it is plausible that PeXTHs exhibit comparable functional conservation. Notably, XTHs from P. euphratica and P. deltoides formed highly supported clades, reflecting pronounced sequence homology and evolutionary conservation of function between these two species.
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Figure 6. Phylogenetic tree of five species of XTH gene family members constructed using the neighbor-joining method. Phylogenetic analysis of XTH family protein sequences from five species (P. euphratica, P. deltoides, P. pruinosa, S. sinopurpurea, and A. thaliana) was performed using the ML (Maximum Likelihood) method by MEGA11 software (version 11.0.13). The value at the branch node represents the bootstrap value (calculated from 1000 repetitions) and shows only values greater than or equal to 50%. The number on the branch represents the branch confidence. Different colored circles represent different species. Species are color-coded as P. deltoides (orange), A. thaliana (blue), S. sinopurpurea (green), P. pruinosa (purple), and P. euphratica (pink); based on the grouping of A. thaliana, XTH was divided into four categories. Each group is distinguished by a different color.
Figure 6. Phylogenetic tree of five species of XTH gene family members constructed using the neighbor-joining method. Phylogenetic analysis of XTH family protein sequences from five species (P. euphratica, P. deltoides, P. pruinosa, S. sinopurpurea, and A. thaliana) was performed using the ML (Maximum Likelihood) method by MEGA11 software (version 11.0.13). The value at the branch node represents the bootstrap value (calculated from 1000 repetitions) and shows only values greater than or equal to 50%. The number on the branch represents the branch confidence. Different colored circles represent different species. Species are color-coded as P. deltoides (orange), A. thaliana (blue), S. sinopurpurea (green), P. pruinosa (purple), and P. euphratica (pink); based on the grouping of A. thaliana, XTH was divided into four categories. Each group is distinguished by a different color.
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2.7. PeXTH Transcriptome Sequencing and Data Analysis

To investigate the response of PeXTH genes to drought stress, we analyzed their transcript levels in P. euphratica seedlings under the drought treatment at 0, 4, and 12 h (Figure 7A). Visualization of the expression data using TBtools revealed that PeuTF07G00088.1 and PeuTF02G02211.1 exhibited the highest transcript abundance among all PeXTH genes. Notably, the expression level of PeuTF07G00088.1 increased in roots but decreased in leaves under drought stress. In contrast, PeuTF02G02211.1 showed declining expression trends in both roots and leaves. These results suggest that PeuTF07G00088.1 may contribute to drought adaptation by enhancing its transcriptional activity in root tissues upon perception of drought signals.
To validate the transcriptome data, the expression patterns of nine PeXTH genes in P. euphratica seedlings under drought stress were analyzed using quantitative real-time PCR (RT-qPCR). The relative expression of 9 genes from different branches of the phylogenetic tree was measured under simulated drought stress of varying durations. After 12 h of treatment, most genes exhibited generally higher expression levels in roots than in leaves. Notably, PeXTH7 (PeuTF07G00088.1) showed significant time-dependent upregulation in both roots and leaves following 4 h and 12 h of treatment with 25% PEG6000, reaching the highest expression level among all examined genes (Figure 7B). This expression trend was consistent with the transcriptome sequencing results. Furthermore, seven genes displayed significantly higher expression in roots compared to leaves at the end of the treatment period. Based on its markedly high expression in both roots and leaves, PeXTH7 (PeuTF07G00088.1) was selected for further functional investigation.

2.8. Subcellular Localization of PeXTH7 in Nicotiana benthamiana

To further investigate the function of PeXTH7 (PeuTF07G00088.1) and determine its subcellular distribution, we performed experimental validation of its localization. Agrobacterium tumefaciens GV3101 harboring the 35S::PeXTH7-YFP construct was infiltrated into N. benthamiana leaves, and the subcellular localization was examined using confocal laser scanning microscopy (Figure 8). The fluorescence signal of 35S::PeXTH7-YFP showed colocalization with both the plasma membrane and endoplasmic reticulum markers. However, following plasmolysis, the 35S::PeXTH7-YFP signal dissociated from the plasma membrane marker. These results indicate that PeXTH7 is synthesized in the endoplasmic reticulum and subsequently functions in the cell wall.

2.9. Effect of PeXTH7 Overexpression on the Regulation of Root System Development in Transgenic A. thaliana

To determine the function of PeXTH7 in root development, we generated transgenic A. thaliana (Col-0) plants overexpressing PeXTH7 driven by the 35S promoter. These plants showed a significant increase in root length. Without sorbitol stress, the overexpression lines exhibited significantly longer primary roots along with an increased density of lateral roots, compared to Col-0 (Figure 9). Under sorbitol-induced osmotic stress, although root growth was suppressed across all lines, the PeXTH7-overexpressing lines consistently developed longer roots and sustained better root growth than Col-0. Statistical analysis of three randomly selected independent lines revealed significantly greater root lengths compared to the wild-type. Our results demonstrate that PeXTH7 promotes root growth and development, which contributes to enhanced drought tolerance.

3. Discussion

3.1. Identification of 33 XTH Family Members in P. euphratica

P. euphratica is predominantly distributed in the Tarim River Basin of Xinjiang, China, where it plays a vital role in maintaining the structure and function of local ecosystems. Through its growth characteristics, it contributes to the regulation of river water resources and serves as an important ecological barrier. Exhibiting remarkable adaptability to the extreme desert conditions of northwestern China, P. euphratica has become a key model species for investigating the molecular and physiological mechanisms of abiotic stress tolerance in woody plants. It holds substantial value for research in related scientific fields.
Plant cell walls represent a unique extracellular matrix primarily composed of cellulose, hemicellulose, and pectin, typically supplemented with structural glycoproteins and lignin [29]. Xyloglucan is the main hemicellulose component of primary cell walls in plants [30]. This highly complex organization renders it a critical player in environmental stress perception. Multiple mechanisms regulate plant drought tolerance, with research by Hoson T demonstrating that the cell wall and plasma membrane collaboratively perceive external stress signals. Upon sensing environmental stresses, the mechanical properties of the cell wall undergo substantial modifications to mitigate adverse conditions [31].
Plant cell wall proteins (CWPs) play a major role in cell wall remodeling and signal transduction. Cell wall proteomics and numerous genetic and biochemical studies have revealed the high diversity of CWPs [32]. Enzymatically active protein components, including glycosidases, proteases, and transferases, occupy a central position in dynamic cell wall restructuring and environmental responses [33,34,35]; these enzymes regulate the assembly and disassembly of cell wall polysaccharide networks through spatiotemporally precise expression patterns [36]. Furthermore, protein–protein and protein–polysaccharide interactions can alter the mechanical properties of the wall and promote its supramolecular assembly [37,38,39]. These findings reveal how plant cells synthesize cell wall polysaccharides, assemble them into a sturdy fiber network, and regulate cell wall expansion during cell growth [40]. Xyloglucan endotransglucosylase/hydrolase (XTH) mediates the cleavage and re-ligation of xyloglucan, a key network component, thereby regulating cell wall extensibility while maintaining its structural integrity. Comparative genomic analyses suggest a non-plant origin for the XTH family, tracing back to Alphaproteobacteria ExoKs—bacterial enzymes involved in biofilm loosening. The earliest XTHs likely evolved in freshwater algae related to Cosmarium through C-terminal extension of EG16-2 proteins [41]. This ancient evolutionary origin established the foundation for its diverse functional roles in land plants. Previous studies have demonstrated that xyloglucan endotransglucosylase/hydrolase (XTH) contributes to cell wall biosynthesis and is closely associated with plant growth, development, and stress resilience, participating in processes such as root elongation [42], leaf venation patterning [43], fruit ripening [44], and responses to biotic and abiotic stresses [45,46].
Research on PeXTH functions remains relatively limited. In this study, we systematically identified XTH family members in four Salicaceae species: 33 in P. euphratica, 28 in P. deltoides, 30 in S. sinopurpurea, and 35 in P. pruinosa. Comparative analysis revealed limited variation in gene copy number among these species. The expansion in P. pruinosa may be attributed to gene duplication events during evolution, whereas the contraction in P. deltoides and S. sinopurpurea likely reflects lineage-specific selection associated with environmental adaptation. Furthermore, bioinformatic analyses of PeXTHs, including sequence conservation, gene structure, and potential functions, provide a theoretical foundation for elucidating the functional mechanisms of this gene family.

3.2. Potential Biological Functions of the PeXTH Gene Family

The XTH gene family plays crucial roles in plant growth and environmental adaptation. Proteins in this family exhibit three characteristic structural domains: (1) the DEIDFEFLG motif, responsible for transferase activity, in which the first glutamic acid (E) residue serves as a binding site essential for catalysis, while the second E functions as a proton donor [47]; (2) the N-glycosylation motif NXT/S, containing serine (Ser) and threonine (Thr) residues adjacent to the catalytic site, which is critical for enzymatic activity; and (3) a C-terminal cysteine residue capable of forming disulfide bonds that significantly contribute to protein structural stability [48]. Studies have revealed that different XTH members exhibit distinct responses to various hormones. Evidence indicates that gibberellic acid (GA3) regulates cell wall elongation by modulating the expression and activity of cell wall-modifying enzymes [49,50]. GA3 treatment of A. thaliana induced upregulation of AtXTH21 expression in A. thaliana [51]. The expression levels of the rose genes RbXTH1 and RbXTH2 were upregulated after ethylene treatment [52]. The expression level of A. thaliana AtXTH23 was significantly upregulated after treatment with abscisic acid (ABA) [15]. These findings collectively elucidate the molecular mechanisms through which the XTH family participates in plant growth, development, and environmental adaptation via specialized hormone regulatory networks.
Cis-acting elements represent specific DNA sequences situated in the 5′ upstream regulatory regions of structural genes, capable of binding transcription factors to modulate gene expression [53]. Analysis of the promoters of the PeXTH gene family revealed that most members contain light-responsive elements (e.g., G-box) and phytohormone-responsive elements (e.g., ABRE and CGTCA-motif), suggesting that their expression is likely regulated by light signaling, abscisic acid (ABA), and methyl jasmonate (MeJA). This inference is supported by previous studies in cherry (Prunus avium L.), where exogenous application of ABA, MeJA, and ethylene significantly upregulated the expression of PavXTH15 [54,55]. Further examination identified that PeXTH promoters also harbor multiple cis-elements associated with abiotic stress responses, including drought-inducible elements (MBS), low-temperature response elements (LTR), and defense stress elements (TC-rich repeats), implying their broad involvement in plant adaptation to environmental challenges. Notably, the PeXTH7 promoter is particularly enriched with stress-responsive elements: the MBS element mediates drought stress responses, while the ABRE element participates in the ABA signaling pathway, which plays a pivotal role in plant adaptation to drought and salt stress [56]. This ABRE-centered regulatory pattern shows remarkable consistency with the XTH gene PagXTH12 in 84K poplar (Populus alba × P. glandulosa) [21], whose promoter also contains ABRE elements and exhibits significant upregulation under drought and salt stress conditions. Moreover, the presence of numerous growth- and development-related regulatory elements further underscores the functional complexity and diversity of this gene family.
A phylogenetic tree constructed using the neighbor-joining method, integrated with interspecies collinearity analysis, revealed high sequence homology and evolutionary conservation of the XTH gene family among closely related species. Phylogenetic classification indicated that Arabidopsis thaliana XTH members were distributed across the Group I/II, IIIA, IIIB, and Ancestral branches with 22, 3, 4, and 4 members, respectively, whereas Populus euphratica contained 23, 5, 4, and 1 members in the corresponding branches. Although the total number of XTH genes was similar between the two species, notable branch-specific distribution differences were observed: P. euphratica exhibited expansion in Groups I/II and IIIA but contraction in the Ancestral branch. This branch-specific expansion and contraction may have resulted from gene duplication or loss events during species differentiation [57]. Despite these interspecific distribution variations, analysis of protein characteristics demonstrated that although XTH proteins exhibit considerable polymorphism in molecular weight, isoelectric point, and amino acid sequence length, members within the same evolutionary branch share highly conserved protein motifs and gene structures, such as exon–intron organization, suggesting functional similarities among clade members. Conserved domain analysis further supported this functional differentiation pattern: 80% of Group IIIA members contain the LamG superfamily domain, whereas nearly all members of Groups I/II and IIIB harbor the GH16_XET functional domain. Gene duplication analysis revealed that the expansion of the PeXTH gene family primarily arose from segmental duplication events. All duplicated PeXTH gene pairs showed Ka/Ks ratios of less than 1.00 (Table 2), indicating that this gene family has undergone strong purifying selection during evolution. This selective pressure maintained relatively slow evolutionary rates and promoted functional conservation. Collectively, these findings demonstrate that the key functional domains and overall architecture of XTH proteins are highly conserved in P. euphratica, with purifying selection playing a critical evolutionary role in maintaining this conservation by effectively eliminating random amino acid mutations that could be detrimental to plant adaptability.
Previous studies have collectively demonstrated that XTH family members exhibit spatiotemporal expression specificity and participate in multiple plant growth and developmental processes, while being regulated by both hormonal and environmental cues [58]. Overexpression of the CaXTH3 gene in Arabidopsis thaliana and chili peppers significantly enhanced transgenic plant tolerance to water loss, accompanied by increased mesophyll cell density and altered leaf morphology [24]. Earlier research also revealed that heterologous expression of a specific P. euphratica XTH gene in tobacco improved drought tolerance by reducing stomatal aperture and consequently decreasing water evaporation [59]. Additionally, studies have shown that A. thaliana Atxth7 mutants exhibit shorter root length than wild-type plants under salt stress [60]. Based on the phylogenetic analysis and RT-qPCR results presented above, PeuTF07G00088.1 (named PeXTH7) was ultimately selected from Populus euphratica for further investigation due to its highest homology with AtXTH7. Under drought stress conditions, PeXTH7 showed sustained upregulation in both roots and leaves, with root tissues displaying significantly higher expression levels than leaf tissues. This tissue-specific expression pattern implies that PeXTH7 may contribute to drought adaptation in P. euphratica primarily through regulating root architecture. Consequently, PeXTH7 has been identified as a principal target for subsequent functional studies aimed at clarifying its precise role in drought resistance mechanisms of woody plants.
Plant growth and development fundamentally depend on cell wall expansion. Xyloglucan, a major hemicellulosic component of the cell wall, has long been a central focus of research. XTH enzymes play essential roles in xyloglucan cleavage and reconnection during cell wall remodeling. The plant XTH family comprises numerous members that are expressed across various tissues and organs, responding to hormonal and environmental stress signals, thereby underscoring their crucial functions in plant growth and adaptation. Although research on XTH genes has achieved considerable progress in recent years, the specific biological functions of this gene family remain incompletely characterized. In this study, we performed a genome-wide analysis of the XTH gene family in P. euphratica, identified all its members, and conducted preliminary predictions regarding the response of PeXTH7 to drought stress. Future work should focus on elucidating the molecular mechanisms through which PeXTH7 contributes to abiotic stress tolerance.

3.3. PeXTH7 Participates in the Regulation of Root Length in Transgenic A. thaliana

To assess whether PeXTH7 shares a conserved role in root growth regulation, we measured root length and lateral root density in PeXTH7-overexpressing A. thaliana plants. The results revealed a significant increase in root length compared to wild-type controls. Given the close relationship between root length and water uptake efficiency, we propose that PeXTH7 may enhance drought tolerance by modulating root elongation through cell wall regulation. However, the precise molecular mechanism underlying this process requires further investigation.

4. Materials and Methods

4.1. Genetic Identification, Physical and Chemical Property Analysis

The XTH protein sequences of Arabidopsis thaliana were retrieved from the TAIR database (https://www.arabidopsis.org/; accessed on 19 November 2024) and used to perform a website BLASTp search against the Populus euphratica protein database (https://ngdc.cncb.ac.cn/search/specific?db=bioproject&q=PRJCA006811; accessed on 19 November 2024) [13], with an E-value threshold set to 1 × 10−5. Subsequently, HMM profiles of the Glyco_hydro_16 (PF00722) and XET_C (PF06955) domains were obtained from the Pfam database (https://pfam.xfam.org/; accessed on 22 November 2024) for local HMM-based screening. The results from both approaches were combined, and sequences that did not simultaneously contain the Glyco_hydro_16 and XET_C domains were filtered out using the online bioinformatics tool NCBI CDD Search (https://www.ncbi.nlm.nih.gov/Structure/bwrpsb/bwrpsb.cgi; accessed on 22 November 2024). The remaining sequences were identified as putative XTH genes of P. euphratica. Based on genomic data available at the National Center for Biotechnology Information (NCBI), XTH family members were also identified in three additional poplar species: P. deltoides  (WV94_445), P. pruinosa (PRJNA863418), and S. sinopurpurea [61].
The physicochemical properties of the identified PeXTH proteins, including coding sequence length, amino acid number, molecular weight, and theoretical isoelectric point, were analyzed using the Expasy ProtParam tool (https://web.expasy.org/protparam/; accessed on 11 September 2024). Subcellular localization of P. euphratica XTH family members was predicted via WOLF PSORT (https://www.genscript.com/; accessed on 11 December 2024). Chromosomal location data were extracted from the genome annotation file, and the physical distribution of XTH genes was visualized using TBtools.

4.2. PeXTH Gene Structure and Conserved Motif Analysis

Conserved motifs in the XTH gene family proteins were analyzed using the MEME online tool (https://meme-suite.org/meme/tools/meme; accessed on 11 September 2024). The analysis was conducted with the optimum motif width set to 10–150 residues and the maximum number of motifs set to 10, while other parameters remained at their default values. The resulting gene structures and motif distributions were visualized using TBtools software (v2.119) for subsequent interpretation.

4.3. Analysis of Cis-Acting Elements of PeXTH Promoter

The promoter sequences of PeXTH genes, defined as the 2000 bp regions upstream of the translation start sites, were extracted using TBtools (v2.119). Putative cis-regulatory elements within these promoter sequences were identified using the PlantCARE database (https://bioinformatics.psb.ugent.be/webtools/plantcare/html; accessed on 18 October 2024). The predicted cis-acting elements were subsequently visualized using TBtools software (v2.119).

4.4. Collinearity and Chromosome Mapping Among Multiple Species

Orthologous gene pairs between P. euphratica and the other four species (P. deltoides, P. pruinosa, S. sinopurpurea, and A. thaliana) were identified using BLASTP alignment. Subsequently, TBtools (version 2.119) software was used to screen for collinearity blocks between P. euphratica and these four species and visualize them.
Chromosome length information (Fasta statistics), PeXTH gene IDs and positional data (GFF3 parsing/text block extraction and filtering), and gene density distribution were extracted from the P. euphratica genome using TBtools (v2.119). Subsequently, chromosomal localization patterns were visualized with the TBtools Gene Position Visualization function, and regional gene distributions were further analyzed using the same module.

4.5. PeXTH Phylogenetic Tree Analysis

Protein sequence clustering and phylogenetic analysis of XTH gene family members from P. euphratica, P. pruinosa, P. deltoides, S. sinopurpurea, and A. thaliana were performed using MEGA11 software (version 11.0.13). The phylogenetic tree was edited and beautified using the iTOL online tool (https://itol.embl.de/, accessed on 19 January 2025).

4.6. Transcriptome Sequencing and Data Analysis of PeXTHs

Transcriptome sequencing data were derived from four-month-old P.euphratica seedlings treated with 25% PEG 6000 and their control conditions. The expression profiles of PeXTHs gene family members were extracted from the quantitative expression data of each treatment [62]. P. euphratica seedlings were treated with a 25% polyethylene glycol 6000 solution, and leaf and root samples were collected at 0, 4, and 12 h post-treatment. The samples were immediately frozen in liquid nitrogen for storage and sequenced using the Ion Proton sequencing platform at the Shenzhen Huada Gene Research Institute. Gene expression levels were calculated using the FPKM (read per million mapped reads per thousand base pairs) method. The RNA-seq data have been uploaded to the NCBI database (https://www.ncbi.nlm.nih.gov/bioproject/PRJNA580347/, accessed on 11 September 2024). Transcriptome data visualization analysis was performed using TBtools software (version 2.119), and the data were subjected to numerical standardization and log transformation. The log transformation parameters were set as follows: base = 2.0; offset = 1.0.
P. euphratica seedlings were grown under a 16-h photoperiod at 25 ± 1 °C and 75% relative humidity, with bi-weekly irrigation. After three months, seedlings were treated with 25% PEG6000 for 0, 4, and 12 h (n = 3 per group). Post-treatment, roots and leaves were sampled, flash-frozen in liquid nitrogen, and stored at −80 °C. Total RNA was extracted using a SPARKscript II RT Plus Kit (SparkJade, Jinan, China), and cDNA was synthesized from 1 µg RNA. RT-qPCR was carried out in 10 µL reactions with SYBR Green mix and gene-specific primers (Table S1). Amplification was achieved using the following cycle settings: 95 °C for 30 s, then 45 cycles of 95 °C for 10 s, 55 °C for 10 s, and 72 °C for 30 s for plate reading. RT-qPCR yielded products between 80 bp and 150 bp in size. After normalization with PeActin, relative expression was assessed. The 2−ΔΔCt method was applied to data evaluation.

4.7. Subcellular Localization of PeXTH7

The constructed 35S::PeXTH7-YFP vector was transformed into Agrobacterium tumefaciens strain GV3101. Strains carrying the target plasmid (CBL-mCherry) were cultured overnight in LB medium supplemented with appropriate antibiotics. Healthy leaves from 4-week-old tobacco plants were selected for infiltration. Agrobacterium cultures containing PeXTH7 and the helper strain 19K (used to enhance fluorescence signals) were grown overnight in LB liquid medium. When the OD600 of the PeXTH7-containing Agrobacterium culture reached 1.0–1.2, cells were harvested by centrifugation at 10,000 rpm for 1–2 min.
The supernatant was discarded and the bacterial cells were collected. An infiltration buffer containing MES, MgCl2·6H2O, and acetosyringone was prepared and adjusted to pH 6.0 using KOH. This buffer was mixed with the Agrobacterium suspension and incubated at 28 °C for 1 h. The bacterial suspension was then infiltrated into the abaxial surface of tobacco leaves, with injection sites clearly marked. Following 24 h of dark treatment, the plants were transferred to a controlled-environment growth chamber for 2–3 days. Subcellular localization was analyzed using a laser scanning confocal microscope (Nikon TS100, Tokyo, Japan). For YFP signal detection, an excitation wavelength of 514 nm was used with emission collection between 524–574 nm. After inducing plasmolysis with 30% sucrose solution, fluorescence distribution was re-evaluated under the same optical settings. For visualization of the endoplasmic reticulum marker, excitation at 587 nm was employed with emission detection in the 597–650 nm range.

4.8. Effect of PeXTH7 Overexpression on Root Length in A. thaliana

The wild-type A. thaliana seeds used in this study was the Columbia-0 (Col-0) ecotype. The PeXTH7 gene was heterologously expressed in Arabidopsis using the pgreenII 0179 (35S NOS)-YFP overexpression vector in the GV3101 Agrobacterium tumefaciens strain, with Escherichia coli—TOP10 used for plasmid propagation. The detailed transgenic methodology followed a previously described protocol [63]. Seeds of the generated lines—Col-0 and three independent PeXTH7-overexpressing lines (OE-1, OE-2, OE-5)—were surface-sterilized and sown on 1/2 MS medium. For each line, 20 seeds were plated per biological replicate, with five replicates established per treatment. A 0 mmol/L sorbitol condition served as the control. After stratification at 4 °C for 2–3 days, the plates were transferred to a growth chamber and positioned vertically. Following 4 days of growth under standard conditions, healthy and uniformly sized seedlings were selected and carefully transferred to fresh 1/2 MS media containing either 0, 100, 200, or 300 mmol/L sorbitol. The seedlings were grown for an additional 5 days, after which representative healthy seedlings from each group were photographed. Primary root length was subsequently measured and analyzed from the images using the software ImageJ (version 1.44p).

5. Conclusions

In this study, a total of 33 PeXTHs genes were identified in P. euphratica, and their gene structures, phylogenetic relationships, collinearity, and cis-acting elements were systematically analyzed. The results indicated that PeXTHs gene family members are involved in drought resistance by regulating root growth and development. RNA sequencing and RT-qPCR analyses further confirmed the critical role of PeXTH7 in the drought stress response. Heterologous overexpression of PeXTH7 in wild-type Arabidopsis significantly promoted root elongation and enhanced drought tolerance. These findings suggest that PeXTH7 may improve drought adaptability in P. euphratica by facilitating root system development. Therefore, this study not only provides a theoretical basis for understanding the function of PeXTHs genes in root growth, but also provides a reference for the subsequent exploration of the molecular response of P. euphratica to abiotic stress.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/plants14243847/s1, Table S1: Primer Sequences for RT-qPCR.

Author Contributions

Conceptualization, P.J. and Z.W.; methodology, J.L., H.J. and T.S.; software, J.L., H.J., T.S., D.M., Q.N. and J.S.; formal analysis, J.L.; writing—original draft preparation, J.L., H.J.; writing—review and editing, J.L., P.J., Z.W., J.S. and Z.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Natural Science Foundation of China, grant numbers 32160355 and 32371838, “Tianshan Talents” Program—Top Telent in Youth Science and Technology (2024TSYCCX0114), “Tianshan Talents” Program—Science and Technology Innovation Team (2023TSYCTD0019), “Xinjiang Tianchi Talents Doctoral Project” (BT-2025-TCYC-0011), Natural Science Support Program of XPCC (2024DA034), and Guidance Program for Science & Technology Projects of XPCC (2024ZD087).

Data Availability Statement

No large datasets were created in this study.

Acknowledgments

We thank Zhongshuai Gai and Xiao Zhang for giving valuable advice during manuscript preparation.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Analysis of gene structure and conserved structural domains of PeXTHs. (A) Distribution of conserved domains in PeXTH. (B) Pefam model of PeXTH; green indicates LamG superfamily, yellow indicates PLN03161 superfamily, and red indicates GH16_XET. (C) Gene structure of PeXTH. Yellow boxes indicate exons, black lines indicate introns, and green indicates non-coding regions. (D) Ten conserved motifs of PeXTHs, with single-letter abbreviations representing amino acids.
Figure 1. Analysis of gene structure and conserved structural domains of PeXTHs. (A) Distribution of conserved domains in PeXTH. (B) Pefam model of PeXTH; green indicates LamG superfamily, yellow indicates PLN03161 superfamily, and red indicates GH16_XET. (C) Gene structure of PeXTH. Yellow boxes indicate exons, black lines indicate introns, and green indicates non-coding regions. (D) Ten conserved motifs of PeXTHs, with single-letter abbreviations representing amino acids.
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Figure 2. Statistics of cis-elements in the PeXTHs promoter region. The number in the figure represents the number of corresponding cis-acting elements predicted in the gene. The color depth and size of the circle are proportional to the number of components. The uncolored circle (number 0) indicates that the component is not detected. The color bars indicate the classification of cis-elements: yellow represents cis-elements related to biotic/abiotic stress, red represents cis-elements related to hormones, green represents cis-elements related to light response, and blue represents cis-elements related to growth and development.
Figure 2. Statistics of cis-elements in the PeXTHs promoter region. The number in the figure represents the number of corresponding cis-acting elements predicted in the gene. The color depth and size of the circle are proportional to the number of components. The uncolored circle (number 0) indicates that the component is not detected. The color bars indicate the classification of cis-elements: yellow represents cis-elements related to biotic/abiotic stress, red represents cis-elements related to hormones, green represents cis-elements related to light response, and blue represents cis-elements related to growth and development.
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Figure 5. Chromosome location. Blue indicates low gene density on the chromosome, while red indicates high gene density on the chromosome.
Figure 5. Chromosome location. Blue indicates low gene density on the chromosome, while red indicates high gene density on the chromosome.
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Figure 7. The expression pattern of PeXTHs under drought stress treatment. (A) Heat map of PeXTHs gene family member expression levels in P. euphratica seedlings under drought stress. Colors represent relative gene expression levels; red indicates high expression and blue indicates low expression. The number in the heat map is the original FPKM value. Pe-R0 represents gene expression levels in roots without drought treatment, and Pe-L0 represents expression levels in leaves without drought treatment. Pe-R4 indicates gene expression levels in roots after 4 h of drought treatment, while Pe-L4 indicates expression levels in leaves under the same conditions. Pe-R12 indicates gene expression levels in roots after 12 h of drought treatment, and Pe-L12 indicates expression levels in leaves under the same conditions. The color scale directly corresponds to the log2 (x + 1) converted value of FPKM. (B) Validation of the transcriptomic data by RT-qPCR is presented. Yellow and green columns represent the gene expression levels in the root and leaf, respectively. Letters (a, b, c, d) mark statistically distinct groups based on Duncan’s multiple range test.
Figure 7. The expression pattern of PeXTHs under drought stress treatment. (A) Heat map of PeXTHs gene family member expression levels in P. euphratica seedlings under drought stress. Colors represent relative gene expression levels; red indicates high expression and blue indicates low expression. The number in the heat map is the original FPKM value. Pe-R0 represents gene expression levels in roots without drought treatment, and Pe-L0 represents expression levels in leaves without drought treatment. Pe-R4 indicates gene expression levels in roots after 4 h of drought treatment, while Pe-L4 indicates expression levels in leaves under the same conditions. Pe-R12 indicates gene expression levels in roots after 12 h of drought treatment, and Pe-L12 indicates expression levels in leaves under the same conditions. The color scale directly corresponds to the log2 (x + 1) converted value of FPKM. (B) Validation of the transcriptomic data by RT-qPCR is presented. Yellow and green columns represent the gene expression levels in the root and leaf, respectively. Letters (a, b, c, d) mark statistically distinct groups based on Duncan’s multiple range test.
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Figure 8. Subcellular localization of the 35S::PeXTH7-YFP protein in tobacco leaf epidermal cells. (A–C) Observation of membrane localization markers co-expressed with PeXTH7 before and after plasmodesmal separation, as well as markers for the endoplasmic reticulum, and fusion images. (A) Before plasmodesmal separation, the cell membrane marker (CBL) overlaps with the YFP fluorescent label carried by PeXTH7. (B) After plasma membrane separation, the cell membrane marker (CBL) separates from the YFP fluorescent label carried by PeXTH7, The region enclosed by the red box exhibits distinct plasmolysis. (C) The endoplasmic reticulum marker (HDEL) fuses with the YFP fluorescent label carried by PeXTH7 (Scale bar = 50 µm).
Figure 8. Subcellular localization of the 35S::PeXTH7-YFP protein in tobacco leaf epidermal cells. (A–C) Observation of membrane localization markers co-expressed with PeXTH7 before and after plasmodesmal separation, as well as markers for the endoplasmic reticulum, and fusion images. (A) Before plasmodesmal separation, the cell membrane marker (CBL) overlaps with the YFP fluorescent label carried by PeXTH7. (B) After plasma membrane separation, the cell membrane marker (CBL) separates from the YFP fluorescent label carried by PeXTH7, The region enclosed by the red box exhibits distinct plasmolysis. (C) The endoplasmic reticulum marker (HDEL) fuses with the YFP fluorescent label carried by PeXTH7 (Scale bar = 50 µm).
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Figure 9. Overexpression of PeXTH7 enhances root system development under simulated drought stress in Arabidopsis. (A) Representative root phenotypes of wild-type (Col-0) and three independent PeXTH7-overexpressing (OE-1, OE-2 and OE-5) lines under sorbitol-induced osmotic stress. Scale bar = 1 cm. (B) Primary root length of the plants shown in (A). (C) Primary lateral root density of the plants shown in (A). Data are presented as mean ± SEM (n ≥ 10). Bars marked with different letters are significantly different (p < 0.05, one-way ANOVA).
Figure 9. Overexpression of PeXTH7 enhances root system development under simulated drought stress in Arabidopsis. (A) Representative root phenotypes of wild-type (Col-0) and three independent PeXTH7-overexpressing (OE-1, OE-2 and OE-5) lines under sorbitol-induced osmotic stress. Scale bar = 1 cm. (B) Primary root length of the plants shown in (A). (C) Primary lateral root density of the plants shown in (A). Data are presented as mean ± SEM (n ≥ 10). Bars marked with different letters are significantly different (p < 0.05, one-way ANOVA).
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Table 1. Physical and chemical properties of the PeXTH gene family.
Table 1. Physical and chemical properties of the PeXTH gene family.
Gene IDMolecular Weight (kDa)Number of Amino Acid (aa)Aliphatic IndexTheoretical pIGrand Average of HydropathicityPredicted Location (s)
PeuTF09G00081.133.0529468.036.15−0.486Cell wall
PeuTF18G00763.133.1929162.718.79−0.411Cell wall
PeuTF07G00088.124.721360.055.95−0.546Cell wall
PeuTF09G01635.132.2828962.775.03−0.362Cell wall
PeuTF06G01644.132.6628769.626.59−0.307Cell wall, Cytoplasm
PeuTF06G01643.132.7628768.957.04−0.356Cell wall, Cytoplasm
PeuTF09G00856.134.129465.318.9−0.494Cell wall
PeuTF08G01082.13833671.375.88−0.346Cell wall
PeuTF01G00675.133.5528959.386.22−0.512Cell wall, Cytoplasm
PeuTF13G00056.123.8321055.815.71−0.561Cell wall, Cytoplasm
PeuTF11G00200.134.9429956.455.09−0.585Cell wall
PeuTF04G00162.134.129356.624.76−0.561Cell wall
PeuTF02G00374.125.6922483.578.51−0.242Cell wall
PeuTF05G01755.133.2429570.758.84−0.322Cell wall, Cytoplasm
PeuTF10G01452.138.2133571.286.07−0.417Cell wall
PeuTF01G01381.139.4933857.439.1−0.559Cell wall
PeuTF11G00627.133.3729271.448.99−0.399Cell wall
PeuTF11G00628.131.5427475.449.67−0.419Cell wall
PeuTF03G01575.13530065.338.4−0.387Cell wall, Cytoplasm
PeuTF14G00471.132.2528266.779.07−0.33Cell wall, Cytoplasm
PeuTF14G00528.130.8226467.958.87−0.539Cell wall, Cytoplasm
PeuTF03G00903.136.331162.779−0.603Cell wall
PeuTF06G01225.133.8829460.759.58−0.443Cell wall
PeuTF02G02211.133.0328866.049.24−0.34Cell wall, Cytoplasm
PeuTF02G02300.133.5529358.65.64−0.606Cell wall
PeuTF06G00688.131.8828562.677.58−0.322Cell wall, Cytoplasm
PeuTF14G00818.134.8831170.846.49−0.251Cell wall
PeuTF19G00986.133.7829669.85.89−0.295Cell wall
PeuTF13G01387.128.1224658.665.8−0.498Cell wall
PeuTF16G00881.134.0329461.79.39−0.426Cell wall
PeuTF18G00888.133.2329271.168.95−0.383Cell wall, Cytoplasm
PeuTF05G00063.133.0129171.414.48−0.261Cell wall, Cytoplasm
PeuTF19G01001.133.7829669.85.89−0.295Cell wall
Table 2. Evolutionary selection pressures of XTHs in P. euphratica.
Table 2. Evolutionary selection pressures of XTHs in P. euphratica.
Gene_1Gene_2KaKsKa/Ks
PeuTF01G01381.1PeuTF03G00903.10.0880299630.3368198850.261356192
PeuTF01G00675.1PeuTF03G01575.10.1367411680.464091460.294642715
PeuTF08G01082.1PeuTF10G01452.10.0524760040.3509120530.149541755
PeuTF06G01643.1PeuTF18G00888.10.2402936932.1650858170.110985759
PeuTF06G01225.1PeuTF09G00081.10.1972618231.2018357730.164133759
PeuTF06G01225.1PeuTF16G00881.10.0388362350.4160443520.093346383
PeuTF19G01001.1PeuTF13G01387.10.0602209850.4462022340.134963432
PeuTF14G00528.1PeuTF02G02300.10.427698912NaNNaN
PeuTF05G01755.1PeuTF11G00627.10.211307847NaNNaN
PeuTF05G01755.1PeuTF02G00374.10.1090485880.5006806190.217800697
PeuTF05G00063.1PeuTF13G00056.10.1267691130.4114061950.30813613
PeuTF02G00374.1PeuTF11G00627.10.233638517NaNNaN
PeuTF04G00162.1PeuTF11G00200.10.0389762140.3650852390.106759218
Non-synonymous is abbreviated as Ka and synonymous is abbreviated as Ks.
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Li, J.; Jin, H.; Song, T.; Miao, D.; Ning, Q.; Sun, J.; Li, Z.; Jiao, P.; Wu, Z. Identification of the Populus euphratica XTHs Gene Family and the Response of PeXTH7 to Abiotic Stress. Plants 2025, 14, 3847. https://doi.org/10.3390/plants14243847

AMA Style

Li J, Jin H, Song T, Miao D, Ning Q, Sun J, Li Z, Jiao P, Wu Z. Identification of the Populus euphratica XTHs Gene Family and the Response of PeXTH7 to Abiotic Stress. Plants. 2025; 14(24):3847. https://doi.org/10.3390/plants14243847

Chicago/Turabian Style

Li, Jing, Hongyan Jin, Tongrui Song, Donghui Miao, Qi Ning, Jianhao Sun, Zhijun Li, Peipei Jiao, and Zhihua Wu. 2025. "Identification of the Populus euphratica XTHs Gene Family and the Response of PeXTH7 to Abiotic Stress" Plants 14, no. 24: 3847. https://doi.org/10.3390/plants14243847

APA Style

Li, J., Jin, H., Song, T., Miao, D., Ning, Q., Sun, J., Li, Z., Jiao, P., & Wu, Z. (2025). Identification of the Populus euphratica XTHs Gene Family and the Response of PeXTH7 to Abiotic Stress. Plants, 14(24), 3847. https://doi.org/10.3390/plants14243847

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