Tree Genetics and Molecular Breeding 2024, Vol.14, No.3, 144-154 http://genbreedpublisher.com/index.php/tgmb 148 gene PalHKT1;2, which is involved in ion transport and homeostasis (Chen et al., 2020). Lastly, the PtGSTF1 gene, encoding a Glutathione S-transferase, improves both biomass production and salt tolerance in Populus trichocarpaby regulating xylem cell proliferation, ion homeostasis, and ROS scavenging (Gao et al., 2022). 5.2 Outcomes of functional verification experiments Functional verification experiments have provided substantial evidence supporting the roles of these genes in salt tolerance. For example, transgenic Populus simonii × P. nigra plants overexpressing PsnHDZ63 displayed better morphological and physiological indexes under salt stress compared to wild-type plants, indicating enhanced salt tolerance (Guo et al., 2021). Similarly, PeERF1 overexpression in Populus alba × Populus glandulosa resulted in improved growth and physiological characteristics under salt stress, further validating its role in salt tolerance (Figure 2) (Ge et al., 2022). Figure 2 Transgenic P. alba×P. glandulosamorphological traits under salt stress (Adopted from Ge et al., 2022) Imagine caption: SE1, SE2, OE1, OE2: various transgenic poplar lines; WT, wild type poplar. (A-D) 1-month-old P. alba × P. glandulosa phenotypes on 0, 50, 75, and 100 mM NaCl rooting media. Under salt stress, the height, root length, and fresh weight were measured in transgenic and WT. The standard deviation is shown by the error bar. The presence of an asterisk implies that there is a substantial difference between transgenic and WT (t-test, * p < 0.05) (Adopted from Ge et al., 2022) Ge et al. (2022) demonstrates the impact of salt stress on transgenic P. alba × P. glandulosa lines compared to wild type (WT). Panel (A) shows the phenotypes of transgenic and WT poplars under different NaCl concentrations (0, 50, 75, 100 mM). Panels (B), (C), and (D) illustrate the measurements of plant height, fresh weight, and root length, respectively. The data reveal that the 35S: PeERF1 transgenic lines exhibit superior growth under salt stress compared to WT, showing significant increases in height, weight, and root length. Conversely, the 35S: SRDX-PeERF1 transgenic lines perform worse than WT under the same conditions. This indicates that overexpression of PeERF1 enhances salt tolerance, while SRDX-PeERF1 reduces it. The error bars and asterisks indicate statistical significance (p < 0.05), highlighting the reliability of the results. This research underscores the potential of genetic modifications in improving salt stress tolerance in poplars. In the case of NAC13, overexpression in Populus alba × P. glandulosa led to significant enhancement in salt tolerance, while antisense suppression resulted in increased sensitivity to salt stress, highlighting the gene's critical function in stress response (Zhang et al., 2019a). Overexpression of PalERF109 in Populus alba var. pyramidalis also confirmed its role in enhancing salt tolerance through the upregulation of PalHKT1;2 (Chen et al., 2020). Furthermore, transgenic Populus trichocarpa plants overexpressing PtGSTF1 showed improved shoot growth, wood formation, and salt tolerance, demonstrating the gene’s multifaceted role in stress adaptation (Gao et al., 2022).
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