Tree Genetics and Molecular Breeding 2024, Vol.14, No.3, 119-131 http://genbreedpublisher.com/index.php/tgmb 121 Non-Fermenting-1-Related Protein Kinase-1) gene in sweet potato (Ipomoea batatas) is involved in drought, salt, and cold tolerance through its role in activating stress-responsive pathways (Figure 1) (Ren et al., 2020). Figure 1 Phenotypic performance and changes in fresh weight (FW) and dry weight (DW) of transgenic sweet potato, wild-type (WT), and empty vector control (VC) plants under different stress conditions (Adapted from Ren et al., 2020) Image caption: The results indicate that under 86 mmol L-1 NaCl or 20% PEG 6000 stress, transgenic plants exhibited significant salt and drought tolerance, continuing to grow and form new leaves and roots, with FW and DW significantly higher than those of WT and VC plants. Under non-stress conditions, there were no significant differences in growth among the groups. This demonstrates that the overexpression of the IbSnRK1 gene significantly enhanced the stress resistance of sweet potato plants, particularly under salt and drought stress (Adapted from Ren et al., 2020) Another important gene, WRKY8, a transcription factor in Solanum lycopersicum, plays a significant role in drought and salt stress tolerance by regulating stress-responsive gene expression and improving osmotic balance under stress conditions (Gao et al., 2019). Moreover, the MaPIP2-7 gene, an aquaporin in banana (Musa acuminata), enhances drought, cold, and salt tolerance by improving water transport and maintaining osmotic balance under stress (Xu et al., 2019). 3.2 Mechanisms by which these genes confer stress resistance The mechanisms by which these genes confer stress resistance in trees often involve complex pathways that regulate gene expression, cellular responses, and physiological adaptations. For example, MbICE1 enhances stress tolerance by upregulating genes involved in the antioxidant defense system, thereby reducing oxidative damage caused by reactive oxygen species (ROS) during drought and cold stress (Duan et al., 2022). Similarly, SnRK1 regulates the ABA (abscisic acid) signaling pathway, which is critical for stomatal closure and osmotic adjustment under drought and salt stress conditions. By modulating these pathways, SnRK1 helps maintain cellular homeostasis and water balance, which are vital for stress tolerance (Ren et al., 2020). The WRKY8 transcription factor, on the other hand, activates stress-responsive genes that lead to the accumulation of osmoprotectants like proline and enhanced antioxidant enzyme activities, thereby mitigating the effects of drought and salt stress (Gao et al., 2019). MaPIP2-7 functions by facilitating water transport across cell membranes, which is crucial for maintaining cell turgor and avoiding dehydration during drought and salt stress. The increased expression of this gene leads to enhanced water retention, reduced membrane injury, and improved overall stress tolerance in the transgenic plants (Xu et al., 2019). 3.3 Comparative analysis of stress resistance genes across different tree species The comparative analysis of stress resistance genes across different tree species reveals both conserved and unique strategies employed by trees to combat environmental stresses. Genes like ICE1 and SnRK1 are found in multiple species, each contributing to stress tolerance through similar yet species-specific mechanisms. For example, while ICE1 in Malus baccata regulates cold and drought tolerance through antioxidant pathways, a similar role is
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