Legume Genomics and Genetics 2025, Vol.16, No.5, 204-214 http://cropscipublisher.com/index.php/lgg 209 (Chen, 2024; Wang et al., 2024b). For instance, in wild soybeans, the overexpression of GsEXPB1 has led to an increase in the number and length of roots, as well as a significant rise in weight. Not only that, but its tolerance to salt stress has also increased. This change is quite revealing-the connection between the activity of expansins and the improvement of root structure and stress adaptation is indeed not accidental. Similar effects have also been observed in other plants. For instance, in tobacco and Brassica plants, once some blotting protein genes (such as NtEXPA4, NtEXPA11, BrEXLB1) are highly expressed, they can push the root system to break through the soil downward, and also help maintain ion balance, enhancing the plant's drought and salt resistance. However, if we knock out certain genes, such as OsEXPA10 in rice, the result changes-the elongation of root cells is significantly reduced, indicating that these genes are actually "indispensable" for normal development (Che et al., 2016). Figure 2 Phenotype of soybean hairy roots overexpressing GsEXLB14 under normal, salt, and drought stress conditions (Bar = 2 cm) (Adopted from Wang et al., 2024a) 6.2 Functional assays linking expansins to cell wall loosening and root architecture What exactly is expansin doing? They do not directly determine how cells grow, but they play a significant role in the "loosening" of cell walls, which is precisely the key link for cells to expand and organs to elongate. Some short-term expression experiments and pilous root transformation studies have found that the expansion protein is indeed located within the cell wall. For instance, when GsEXPB1 of soybeans is overexpressed in hairy roots, the roots not only grow faster but also can better cope with salt stress. Not only that, experiments on other model plants such as Arabidopsis thaliana have also made similar findings-seeds germinate more easily, root hairs grow
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