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CIMBCurrent Issues in Molecular Biology
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3 July 2026

14 Pages

Research Progress on the Regulatory Mechanisms of Salt-Stress Response and Functional Genes in Populus

and
College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China
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Curr. Issues Mol. Biol.2026, 48(7), 684;https://doi.org/10.3390/cimb48070684
This article belongs to the Special Issue Molecular Mechanisms and Omics Approaches in Plant Stress Tolerance
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Abstract

Soil salinization represents one of the most severe abiotic constraints on global forest productivity. Populus, the most widely cultivated fast-growing timber tree and a premier model woody plant, exhibits striking intrageneric variation in salt tolerance—from the extremely halophytic Populus euphratica to highly salt-sensitive cultivated clones. Understanding the molecular basis of this variation has profound implications for saline–alkali land reclamation and salt-tolerant variety breeding. This review systematically synthesizes current knowledge on Populus salt-stress responses, covering three primary injury mechanisms (osmotic stress, ionic toxicity, and oxidative damage) and the corresponding physiological countermeasures. We further survey functional genes across four major categories: ion transporters, osmotic-adjustment enzymes, antioxidant-defense components, and transcription factors. Crucially, we extend beyond the herbaceous-plant paradigm by examining salt-tolerance strategies that are specific to the woody architecture of Populus: long-distance radial and axial Na+ transport through tall stems, salt sequestration in senescent bark and wood parenchyma, and deep-root ion exclusion strategies. Comparative insights from other woody genera are incorporated to highlight convergent and divergent mechanisms. On this basis, we propose an integrated multi-level regulatory model in which Na+ compartmentalization/efflux serves as the core, ROS homeostasis as the key regulatory axis, and osmotic adjustment as the auxiliary strategy. Outstanding challenges—including unresolved primary salt-signal perception, insufficient pathway integration, and limited in planta gene-function verification—are critically assessed, and future research priorities encompassing multi-omics integration, CRISPR-based gene editing, and natural-population genomics are outlined.

1. Introduction

Soil salinization is one of the foremost abiotic stress factors constraining the sustainable development of global agriculture and forestry. Approximately 20% of arable land and over 50% of irrigated farmland are threatened by salinity damage, and the affected area continues to expand owing to climate change and unsustainable irrigation practices [1]. In this context, the development of salt-tolerant plant varieties has become a research priority of considerable scientific and economic importance. Salt stress imposes osmotic stress, ionic toxicity, and secondary oxidative damage on plant cells, activating a complex multi-tiered signaling and response network spanning from ion transport and osmotic adjustment to transcriptional reprogramming [2,3].
Salt stress exerts a tripartite deleterious effect on plant physiology. The initial osmotic phase reduces soil water potential, rapidly impeding root water uptake and triggering stomatal closure, which in turn limits photosynthetic carbon assimilation and growth. The subsequent ionic phase is characterized by the progressive accumulation of Na+ and Cl− in the cytosol to toxic concentrations, disrupting enzyme activity, protein synthesis, and membrane integrity, while simultaneously impairing the uptake of essential nutrients such as K+, Ca2+, and NO3− through competitive ion transport. These ionic imbalances, combined with stomatal limitation of CO2 fixation, lead to the overproduction of reactive oxygen species (ROS) including superoxide (O2−), hydrogen peroxide (H2O2), and hydroxyl radicals (OH−), causing oxidative damage to lipids, proteins, and nucleic acids—constituting the third, oxidative phase of salt stress [2,4]. Plants have evolved a coordinated suite of adaptive strategies to counter these stresses, including osmotic adjustment through compatible solute accumulation, ion homeostasis via regulated transport and compartmentalization, and enzymatic and non-enzymatic antioxidant defense systems [5,6]. The molecular basis of these mechanisms has been extensively characterized in herbaceous model plants such as Arabidopsis thaliana and rice; however, woody perennials such as Populus present additional structural and physiological features—tall stature, perennial life history, extensive secondary growth, and deep root systems—that modulate salt-stress responses in ways not captured by herbaceous models.
Populus, belonging to the family Salicaceae, is the most widely distributed fast-growing timber genus and is established as the premier model system for molecular biology research in forestry. Among its members, Populus euphratica Olivier is a remarkable halophyte capable of surviving in soils with up to 5% NaCl, whereas most cultivated clones are highly salt-sensitive. This intrageneric contrast makes Populus an exceptionally tractable system for dissecting the genetic architecture of salt tolerance in woody plants. Earlier reviews have provided a broad overview of the physiological and molecular responses of Populus to salt stress [7], laying important groundwork that the present review extends by incorporating recent gene-function studies and an explicit woody-plant-specific perspective.
The completion of the P. trichocarpa reference genome [8] and subsequent multi-omics studies have propelled rapid advances in our understanding of Populus salt tolerance at the molecular level. However, most mechanistic discussions have been framed within a herbaceous-plant paradigm, overlooking physiological and structural features unique to woody species—such as tall stature with long-distance ion transport, radial growth generating new xylem and phloem annually, senescent bark accumulating salts, and deep-root systems that differentially encounter soil salt gradients. A comprehensive review that integrates the herbaceous-plant molecular framework with woody-plant-specific characteristics is therefore overdue.
This review systematically summarizes recent advances in the molecular mechanisms of Populus salt tolerance, with explicit attention to woody-plant-specific mechanisms and a comparative perspective spanning other arboreal taxa. We propose an integrated multi-level regulatory model and identify outstanding scientific challenges alongside promising research directions, aiming to provide a theoretical foundation and technical insights for molecular breeding of salt-tolerant. Specifically, this review aims to: (i) provide a comprehensive catalog of functionally validated salt-tolerance genes in Populus, organized by functional category—ion transporters, osmotic regulators, antioxidant enzymes, and transcription factors; (ii) critically evaluate the extent to which molecular mechanisms characterized in herbaceous model systems apply to, or require modification for, woody perennials; (iii) synthesize these findings into an integrated multi-level regulatory model that unifies ion homeostasis, osmotic adjustment, ROS detoxification, and hormone signaling under a hierarchical framework; and (iv) identify critical knowledge gaps and propose experimentally tractable research priorities that leverage emerging genomic and gene-editing tools. While a recent review has addressed salt, drought, and heavy-metal stress responses in Populus alba and its hybrids [9], the present review is distinguished by its specific focus on woody-plant-specific anatomical and physiological characteristics of Populus—including long-distance Na+ transport through tall stems, bark-mediated salt sequestration, and deep-root ion exclusion—which are absent from herbaceous model systems and not covered in depth by prior reviews. Furthermore, this review explicitly proposes an integrated multi-level regulatory model, a conceptual framework that hierarchically connects Na+ compartmentalization/efflux (core), ROS homeostasis (key regulatory axis), and osmotic adjustment (auxiliary strategy) with transcriptional co-regulation by multiple transcription factor families.
A substantial number of previously published reviews on Populus salt, drought, and heavy-metal stress responses were identified during the search process and critically evaluated. While these earlier syntheses provided valuable groundwork, the present review is distinguished by its exclusive focus on woody-plant-specific anatomical and physiological features—tall-stature ion transport, secondary growth dynamics, bark-mediated ion sequestration, and ectomycorrhizal symbiosis—that are systematically underrepresented in both herbaceous model-centric reviews and prior broad-stress surveys of Populus.

2. Physiological Responses of Populus to Salt Stress

Through long-term adaptive evolution, Populus has developed a multi-level physiological response system to salt stress, integrating ion homeostasis regulation, osmotic adjustment, antioxidant defense, and phytohormone signaling to collectively mitigate the triple damage of osmotic stress, ionic toxicity, and oxidative damage.

2.1. Ion Homeostasis Regulation

Maintaining intracellular ion homeostasis is central to Populus salt tolerance, achieved through coordinated regulation of Na+/K+ balance and suppression of cytoplasmic Na+ toxicity via multiple complementary pathways.
The Salt Overly Sensitive (SOS) signaling pathway constitutes the primary Na+-exclusion mechanism and is highly conserved in P. euphratica. Upon salt perception, a transient rise in cytoplasmic Ca2+ activates Calcineurin B-Like (CBL) proteins and their interacting kinases (CIPKs), forming a complex that phosphorylates and activates the plasma-membrane Na+/H+ antiporter SOS1, thereby driving extracellular Na+ efflux from root cells [10]. Vacuolar Na+ sequestration via NHX antiporters represents a complementary strategy: PeNHX1, PeNHX2, and PeNHX5 are constitutively highly expressed in leaves and are further up-regulated under salt stress, facilitating Na+ compartmentalization into the vacuole [11]. Members of the High-affinity K+ Transporter (HKT) family limit long-distance Na+ transport to the shoot by modulating xylem loading, thereby protecting photosynthetic tissues from ionic toxicity [12].
The CBL-CIPK network further participates in ion homeostasis through regulation of multiple transport proteins. PeCBL4 interacts with PeCIPK24 and PeCIPK26, activating SOS1-mediated Na+ efflux under salt stress [13]. Calcium-dependent protein kinases PeCPK7 and PePKS5 enhance Na+ efflux and K+ influx in Arabidopsis root cells when overexpressed, maintaining K+/Na+ balance and improving salt tolerance [14].

2.2. Osmotic Adjustment

Osmotic adjustment is a critical strategy for counteracting salt-stress-induced water deficit. Populus accumulates compatible solutes—including proline, glycine betaine, soluble sugars (sucrose, trehalose), and raffinose-series oligosaccharides—to lower cellular osmotic potential, maintain turgor pressure, and stabilize membranes and enzymes.
Proline is the predominant osmoprotectant under salt stress; its content in P. euphratica leaves rises progressively with increasing NaCl concentration, closely correlated with induction of pyrroline-5-carboxylate synthetase (P5CS) gene expression [15]. Galactinol synthase genes GolS1 and GolS2 are markedly induced by salt treatment, enhancing synthesis of galactitol and raffinose and expanding the repertoire of osmoprotectants [16]. Betaine aldehyde dehydrogenase (PeBADH) and choline monooxygenase (PeCMO) act synergistically to sustain betaine biosynthesis, with PeCMO transcript levels increasing more than eight-fold in roots under salt stress [17]. Soluble-sugar synthesis genes PeSPS (sucrose phosphate synthase) and PeTPS (trehalose-6-phosphate synthase) are likewise significantly up-regulated, collectively enhancing cellular osmotic capacity [18]. Notably, the hybrid P. talassica × P. euphratica coordinates osmoprotectant synthesis across aboveground and belowground tissues at low salinity, but this coordinated response is significantly impaired at high salt concentrations, illustrating that osmoregulatory efficiency is tightly constrained by the severity of salt stress [19].

2.3. Antioxidant Defense

Salt stress triggers overproduction of reactive oxygen species (ROS), which cause oxidative damage to membranes, proteins, and nucleic acids. Populus counters this challenge through a multi-tiered antioxidant system comprising both enzymatic and non-enzymatic components.
The enzymatic antioxidant cascade is anchored by superoxide dismutase (SOD), which converts O2− to H2O2; catalase (CAT) and peroxidase (POD) then reduce H2O2 to H2O; ascorbate peroxidase (APX) and glutathione peroxidase (GPX) further contribute to redox detoxification. In 84K Populus, antioxidant enzyme activities initially increase and then decline with escalating NaCl concentration, indicating that moderate salinity is manageable whereas severe salinity overwhelms enzymatic capacity [20]. Tissue-specific transcriptomics revealed that root redox-related genes are most significantly enriched, designating the root as the primary ROS-scavenging organ [21].
Glutathione S-transferase PeGSTU58, localized in both the cytoplasm and nucleus, is up-regulated under salt stress. Its overexpression in transgenic Arabidopsis elevates the activities of SOD, POD, CAT, and GST while up-regulating stress-responsive genes DREB2A and COR47 [22]. Overexpression of the peroxisome-proliferation gene PePEX11 reduces H2O2 accumulation, highlighting a peroxisome-mediated contribution to ROS metabolism [23]. Non-enzymatic antioxidants—glutathione (GSH), ascorbic acid (ASA), and flavonoids—directly scavenge ROS and interact synergistically with the enzymatic system to maintain redox homeostasis [20].

3. Woody-Plant-Specific Mechanisms of Salt Tolerance in Populus

The discussion of plant salt tolerance has historically been dominated by findings from the herbaceous model species Arabidopsis thaliana and cereal crops. While the core ion-homeostasis and osmotic-adjustment pathways are largely conserved, Populus and other woody plants possess structural and physiological characteristics that generate both unique challenges and additional adaptive solutions unavailable to short-lived annuals. These wood-specific mechanisms deserve explicit consideration in any comprehensive review of Populus salt tolerance.

3.1. Long-Distance Ion Transport in Tall Trees

In tall trees such as Populus, Na+ absorbed by root cells must traverse a substantially greater axial distance to reach photosynthetically active canopy tissues compared with herbaceous plants. This long-distance transport is mediated primarily through the xylem stream, making the regulation of xylem Na+ loading a critical checkpoint for salt tolerance. HKT1-type transporters, which retrieve Na+ from the xylem apoplast back into surrounding parenchyma cells, are therefore of particular physiological importance in Populus. Overexpression of PeHKT1;1 significantly reduces Na+ accumulation in leaves of transgenic Populus [24], consistent with a “recirculation” model in which Na+ unloaded by xylem parenchyma HKTs is redirected to the phloem for basipetal retranslocation to roots.
Radial ion transport across multiple wood rings presents an additional complexity absent in herbaceous species. As secondary xylem (wood) is formed annually through cambial activity, Na+ stored in the symplast of living ray parenchyma and axial parenchyma of older wood can act as a long-term sink, buffering fluctuations in apoplastic salt concentration. This buffering capacity increases with tree maturation, potentially explaining why adult P. euphratica trees tolerate higher salt concentrations than seedlings. The molecular regulation of wood-parenchyma Na+/H+ antiporters (tonoplast NHX and vacuolar H+-ATPase/PPase) in this context remains largely unexplored and represents a priority for future research as it remains insufficiently characterized. While some progress has been made—DNA methylation changes under salt stress have been reported in Populus [25], non-coding RNAs (miRNAs, lncRNAs) have been identified as regulators of salt tolerance in multiple Populus species [26], and ubiquitylation and phosphorylation have been documented in Populus stress responses [27,28]—systematic and integrated multi-layered epigenomic profiling specifically under salt stress remains limited. Evidence from other plant systems further underscores the importance of these regulatory layers in salt-tolerance responses [29,30,31]. Comprehensive profiling in Populus is likely to reveal additional regulatory dimensions not captured by transcriptomics alone.

3.2. Salt Sequestration in Bark and Senescent Tissues

A distinctive feature of woody plants is the presence of bark—comprising the phloem, cortex, and periderm—as a substantial carbon and mineral reservoir. In salt-stressed Populus, the outer bark and older phloem tissues have been reported to accumulate Na+ and Cl− at concentrations substantially higher than those in living mesophyll cells [21], suggesting that these metabolically less active tissues serve as a salt dump protecting the photosynthetic canopy. This mechanism is analogous to the salt-bladder strategy employed by halophytes such as Atriplex and Mesembryanthemum, but operates via a fundamentally different anatomical compartment—the secondary phloem and bark parenchyma. Periodic bark shedding in Populus may therefore constitute a passive salt-excretion mechanism, although direct experimental evidence for this hypothesis is lacking and warrants investigation through isotopic-tracer studies combined with laser-ablation ICP-MS.
Comparisons with other broad-leaved trees support the importance of bark salt storage: Quercus suber (cork oak) accumulates substantial Na+ in its thick bark under saline irrigation [32], and the mangrove Avicennia marina secretes excess salt via specialized bark-associated salt glands [33]. Although Populus lacks dedicated salt glands, the principle of peripheral-tissue salt storage appears to be a broadly convergent woody-plant strategy.

3.3. Deep Root Systems and Soil Salt Avoidance

The deep, extensive root architecture of Populus confers a spatial advantage over herbaceous crops: deep roots can access water from below the saline zone, effectively practicing salt avoidance by reducing total Na+ uptake. P. euphratica in its natural riparian habitat of the Tarim Basin exploits this strategy to access deep freshwater reserves during drought, while surface soils are highly saline [19]. Root plasticity—including preferential growth into low-salinity sub-horizons—is regulated by root gravitropism and hydrotropism pathways. PagMYB73A promotes adventitious root elongation in 84K Populus under salt stress [34], and the hormonal control of root architecture under salinity remains an active and promising research area.

3.4. Mycorrhizal Associations and Salt Tolerance

Mycorrhizal associations—ubiquitous in forest trees but rare or absent in most herbaceous model plants [35]—further augment salt tolerance of Populus by improving water and nutrient acquisition, modifying rhizosphere chemistry, and directly attenuating Na+ uptake [36]. Ectomycorrhizal fungi associated with P. tremula and P. euphratica have been shown to reduce foliar Na+ concentrations under salt stress [37,38], pointing to a tripartite root–mycorrhiza–salt-tolerance interaction that is an intrinsic component of woody-plant salt biology but has no parallel in Arabidopsis or rice research.

3.5. Comparative Perspectives with Other Woody Species

Comparing Populus with other gymnospermous and angiospermous trees illuminates both shared principles and genus-specific adaptations. In Pinus (conifers), salt tolerance is achieved primarily through tight root exclusion and accumulation of polyols (mannitol, pinitol) as osmoprotectants, with NHX vacuolar antiporters also playing important roles in the needles [39]. Unlike Populus, conifer needles possess limited vacuolar volume for Na+ storage, and thick cuticular waxes reduce salt spray absorption—a relevant adaptation in coastal Pinus species. In Quercus (oaks), transcriptomic responses to salinity share core components with Populus (SOS pathway induction, ERF and WRKY activation) but show markedly lower induction of NHX and HKT genes, consistent with the relatively lower salt tolerance of most oak species [36]. The extreme salt tolerance of Tamarix (tamarisk)—a dicotyledonous tree that can withstand NaCl concentrations exceeding 3%—is achieved through specialized salt glands on leaves and stems that actively excrete Na+ and Cl−; transcriptomic studies have identified WRKY and MYB transcription factors among the differentially expressed genes in Tamarix under salt stress, suggesting potential convergence with Populus stress-response pathways. These cross-species comparisons underscore the value of a comparative tree biology framework for identifying mechanistic innovations specific to Populus and for pinpointing candidate genes that could be transferred to improve salt tolerance in other timber species.

5. An Integrated Multi-Level Regulatory Model of Salt Tolerance in Populus

Comprehensive synthesis of existing research demonstrates that salt tolerance in Populus is not governed by any single pathway but arises from the coordinated operation of a hierarchical multi-level regulatory network. Ion homeostasis—centered on Na+ vacuolar sequestration (NHX) and plasma-membrane efflux (SOS1)—forms the primary defensive core, ensuring that cytoplasmic Na+ concentrations remain below toxic thresholds. Osmotic adjustment, mediated by the coordinated synthesis of proline, betaine, raffinose, and soluble sugars, maintains cellular water potential and provides auxiliary support for stress adaptation. The antioxidant defense network—comprising enzymatic (SOD/CAT/APX/POD/GPX/GSTU) and non-enzymatic (GSH/ASA/flavonoids) components—eliminates ROS overproduction, preventing irreversible oxidative damage to macromolecules. These three functional modules are integrated by Ca2+ and ABA signaling nodes and are transcriptionally co-regulated by overlapping sets of ERF, MYB, WRKY, NAC, and bZIP transcription factors.
Critically, the woody architecture of Populus imposes an additional spatial dimension on this model: long-distance Na+ transport through tall stems demands HKT-mediated xylem retrieval at multiple points along the vascular axis, bark parenchyma provides a peripheral Na+ sequestration compartment supplementing vacuolar storage in leaf mesophyll, and deep roots can exploit spatial salt gradients in the soil profile. These tree-specific features are not merely additive but mechanistically integrated with the core molecular network: bark NHX expression is co-regulated by the same CBL-CIPK calcium-signaling module that controls SOS1 in roots, and wood-ray parenchyma tonoplast H+-ATPase activity energizes vacuolar Na+ sequestration using the same biochemical machinery as leaf mesophyll vacuoles.
The proposed multi-level model has important implications for the molecular breeding of salt-tolerant Populus varieties. First, the hierarchical organization of the model suggests that simultaneous modulation of the core Na+ exclusion module (SOS1/NHX/HKT) and the ROS regulatory axis (antioxidant enzymes/transcription factors) is likely to produce synergistic, rather than merely additive, improvements in salt tolerance—a prediction testable through combinatorial transgenic approaches. Second, recent genome-wide studies in P. euphratica have identified expanded gene families—including C2H2 zinc-finger proteins, aspartic proteases, and glycine-rich RNA-binding proteins—whose members exhibit salt-responsive expression patterns [57], providing a rich source of candidate genes for functional validation and breeding. Third, the cross-talk between hormone signaling pathways and the core salt-tolerance modules—particularly the ABA-dependent activation of MYB and NAC transcription factors and the JA-mediated modulation of antioxidant gene expression [42]—offers opportunities for hormone-based priming strategies to enhance salt tolerance in Populus plantations. Comparative analysis with salt-tolerant woody species outside Salicaceae—such as Avicennia marina (mangrove) and Casuarina spp.—further suggests that salt secretion via specialized glands and symbiotic nitrogen fixation under saline conditions represent alternative evolutionary strategies whose molecular underpinnings may inform orthogonal breeding approaches for Populus.

6. Current Challenges and Future Directions

Despite remarkable progress, several fundamental challenges persist in the study of Populus salt tolerance.
The primary molecular sensors of salt stress at the plasma membrane remain poorly characterized. The identity of the initial Na+ sensor and the mechanisms coupling ionic and osmotic perception to intracellular signaling cascades remain unclear, limiting our understanding of how salt signals are first decoded in Populus cells. Candidates emerging from Arabidopsis research—including the MSCL-like mechanosensitive channels and the OSCA family of hyperosmolality-gated Ca2+-permeable channels—require functional validation in Populus.
The temporal and environmental regulation of cross-talk among ion-homeostasis, osmotic-adjustment, and antioxidant pathways remains insufficiently characterized. In particular, the hormonal interaction network—ABA, ethylene, JA, and brassinosteroids—and its context-dependent modulation of salt-tolerance gene expression requires systematic investigation using high-resolution time-course transcriptomics and hormone-signaling mutants in Populus. The transcriptional regulation of salt-stress responses by these hormones has been documented in herbaceous species [43], but systematic characterization in Populus remains a priority.
Functional validation of salt-tolerance genes remains predominantly dependent on the Arabidopsis heterologous system, which lacks the woody architecture and perennial physiology of Populus. Direct in planta validation using stable transgenic Populus lines, combined with CRISPR/Cas9-mediated knockouts in P. euphratica itself, is essential for translating molecular discoveries into actionable breeding targets.
The roles of epigenetic regulation (DNA methylation, histone modifications), small and long non-coding RNAs (miRNAs, lncRNAs, circRNAs), and protein post-translational modifications (ubiquitylation, SUMOylation, phosphorylation) in the systemic salt-tolerance response of Populus have been largely unexplored. Multi-layered epigenomic profiling under salt stress is likely to reveal additional regulatory dimensions not captured by transcriptomics alone.
Looking forward, four research directions are prioritized: (i) multi-omics integration—combining transcriptomics, metabolomics, proteomics, and epigenomics within a systems-biology framework to reconstruct the full topology of the Populus CRISPR-based gene editing applications (including Cas9-mediated knockout, base editing, and prime editing) salt-response regulatory network; (ii) in Populus to conduct precise functional validation and rational engineering of salt-tolerance genes; (iii) population genomics of P. euphratica and its wild relatives to discover superior salt-tolerance alleles via genome-wide association studies; and (iv) translational breeding—leveraging marker-assisted selection, genetic transformation, and gene editing to develop elite Populus varieties adapted to saline–alkali soils, thereby supporting ecological restoration and sustainable forestry on salt-affected land.

7. Conclusions

This review provides a comprehensive synthesis of the molecular mechanisms underlying salt tolerance in Populus, organized within a hierarchical multi-level regulatory framework. The central thesis emerging from this synthesis is that salt tolerance in woody perennials cannot be reduced to any single molecular pathway—rather, it arises from the coordinated integration of ion homeostasis, osmotic adjustment, ROS detoxification, and hormone-mediated transcriptional regulation, all operating within a woody anatomical context that uniquely modulates these processes. The proposed model identifies Na+ vacuolar sequestration and plasma-membrane efflux as the primary defensive core, antioxidant networks as the central regulatory axis, and osmotic adjustment as a critical auxiliary support system, with CBL-CIPK calcium signaling and ABA-dependent transcription factors providing integrative control across all levels.
Several critical knowledge gaps remain that should guide future research. The identity of the primary Na+ sensor(s) in Populus has yet to be conclusively determined, and the structural basis of ion channel gating under salt stress awaits high-resolution characterization. The regulatory contributions of epigenetic modifications—DNA methylation, histone modification, and non-coding RNAs—to salt-responsive gene expression in Populus remain insufficiently characterized. The mechanistic basis of ectomycorrhiza-mediated salt tolerance improvement, though demonstrated physiologically, lacks molecular dissection. Bridging these gaps through the application of CRISPR-based gene editing, single-cell transcriptomics, and multi-omics integration holds transformative potential for both fundamental understanding and applied breeding of salt-tolerant forest trees.
In the broader context of global environmental change, the molecular breeding of salt-tolerant Populus varieties represents a strategic priority. Saline–alkali land occupies over 900 million hectares worldwide and continues to expand. As fast-growing woody perennials with well-developed genomic resources and established transformation protocols, salt-tolerant Populus cultivars offer a tangible pathway toward ecological restoration, carbon sequestration, and sustainable biomass production on marginal lands that are unsuitable for conventional agriculture.

Author Contributions

Conceptualization and writing—original draft: P.H.; supervision, writing—review and editing, and funding acquisition: H.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (grant number 32370377).

Data Availability Statement

No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Acknowledgments

During the preparation of this manuscript, the authors used AI-assisted tools (including large language models) solely for language polishing, grammar checking, and improving the clarity of written English. All scientific content, literature analysis, interpretation, and conclusions were generated and verified by the authors. The authors take full responsibility for the scientific accuracy and integrity of this work.

Conflicts of Interest

The authors declare no conflicts of interest.

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