Improving plant water use efficiency (WUE) and drought tolerance by modulating stomatal activity constitutes a promising strategy for mitigating the impacts of water scarcity. SnRK2, a key component of the abscisic acid (ABA) signaling pathway, plays a critical role in modulating stomatal behavior under abiotic stress. However, the functional role of SnRK2 in regulating stomatal movement to enhance WUE and drought tolerance in Populus euphratica remains to be characterized. In this study, 11 PeSnRK2 genes were identified in the P. euphratica genome, each comprising 9–14 exons and exhibiting an uneven distribution across seven chromosomes. Subcellular localization predictions indicated that these proteins are predominantly localized in the Cytoplasm and Cytoskeleton. Phylogenetic analysis grouped the PeSnRK2 genes into three distinct subfamilies, and conserved gene structures were observed within each clade. Analysis of cis-acting regulatory elements suggested that PeSnRK2 genes were involved in hormonal signaling and stress response pathways. Further transcriptomic data also indicated substantial alterations in PeSnRK2 expression due to polyethylene glycol (PEG) and abscisic acid (ABA) treatment. Finally, qRT-PCR and subcellular localization showed that PeSnRK2.6 is highly induced by ABA and functions in both nucleus and cytoplasm. This first characterization in a desert woody species bridged gaps in SnRK2 evolution and function.

NIN-like protein (NLP) transcription factors are key regulators of plant nitrate signaling and stress responses. Although extensively studied in Arabidopsis thaliana and various crops, it has rarely been reported in woody plants, particularly in drought-tolerant tree species. In this study, 10 PeNLP genes were identified in the drought-tolerant tree Populus euphratica Oliv. through comparative genomics. These genes were unevenly distributed across seven chromosomes, and the gene-family expansion was mainly driven by whole-genome duplication (WGD). Analysis of conserved domains showed that PeNLPs contained 4–10 characteristic motifs, and most members possessed the typical RWP-RK and PB1-related domains. Collinearity analysis identified 18 NLP orthologous gene pairs between P. euphratica and its relatives (Populus pruinosa and Salix sinopurpurea), which exceeded the 15 pairs detected between P. euphratica and A. thaliana, indicating that the NLP family is more conserved within the Salicaceae. Phylogenetic analysis divided PeNLPs into three subfamilies, and their promoter regions harbored diverse cis-acting elements associated with hormone signaling, environmental stress, growth, and light response. Transcriptome and qRT-PCR analyses further demonstrated that PeNLPs were generally downregulated under drought stress. Overall, this study systematically characterized the evolution, structure, and drought responsiveness of the PeNLPs, providing a theoretical basis and genetic resources for improving nitrogen use efficiency and drought resistance in trees.

Auxin plays a crucial role in plant growth and development via concentration gradient regulation, with auxin response factors (ARFs) as key transcription factors in its signalling pathway. However, comprehensive identification and characterisation of ARF genes in Salicaceae remain limited. This study performed a genome-wide analysis of ARF genes in three Salicaceae species (Populus euphratica Oliv., Populus pruinosa, and Salix sinopurpurea), aiming to clarify their physicochemical properties, evolutionary relationships, and functional relevance. A total of 34 ARF genes were identified in each species, all being nucleus-localised hydrophilic unstable proteins clustered into six phylogenetic subgroups. Their promoters contain numerous cis-acting elements responsive to light, phytohormones, and stresses. Transcriptome and qRT-PCR data showed significant up-regulation of PeARF18 in ovate/broad-ovate leaves of P. euphratica compared to linear/lanceolate leaves. This study provides preliminary insights into the characterisation and potential role of the Salicaceae ARF gene family, laying a foundation for further functional exploration of PeARF18 in P. euphratica leaf shape development.

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.

Drought stress triggers significant adaptive responses in plant morphology and physiology. As a representative xerophytic genus, Zygophyllum possesses distinct drought-adaptive traits in morphology, anatomical structure and physiological metabolism. This study examined the responses of three Zygophyllum species (Zygophyllum fabago, Zygophyllum brachypterum, and Zygophyllum obliquum) to progressive osmotic stress induced by 20% PEG-6000 over 28 days under controlled conditions. Among the three species, Z. brachypterum displayed the greatest tolerance, as evidenced by its lowest wilting rate, longest root elongation, and more stable leaf anatomical traits under stress, despite a general decrease in all measured structural parameters across species. Physiologically, Z. brachypterum showed the smallest reduction in leaf water content (5.99% vs. 13.51% in Z. fabago and 20.31% in Z. obliquum), the smallest increase in relative electrolyte leakage (126.72% vs. 172.84% and 162.91%, respectively), lower excised-leaf water loss, and sustained higher photosynthetic rates during later stress stages. It also accumulated the lowest levels of total reactive oxygen species (ROS) and malondialdehyde (MDA), alongside the highest proline content and the highest activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Based on a comprehensive evaluation integrating multiple morphological, anatomical, photosynthetic, antioxidant, and osmotic-adjustment indicators through principal component analysis and membership function analysis, the drought-resistance ranking at the seedling stage was determined as Z. brachypterum > Z. fabago > Z. obliquum. The superior tolerance of Z. brachypterum was associated with its more stable leaf structure, enhanced water retention, sustained late-stage photosynthesis, and stronger antioxidant and osmotic adjustment capacities. These findings provide physiological insights into PEG-induced osmotic stress tolerance in Zygophyllum seedlings.