Tree Genetics and Molecular Breeding 2025, Vol.15, No.3, 117-127 http://genbreedpublisher.com/index.php/tgmb 123 8 Case Study: Functional Characterization of PtWOX5 in Lateral Root Formation 8.1 Background and identification of the candidate gene The WOX gene family plays a very important role in the development of plant roots. Studies have found that in poplar trees, PtWOX5 (such as PtoWOX5a) is particularly expressed at the root tips and lateral root tips during adventite and lateral root regeneration, suggesting that it may be involved in the maintenance of root meristem and the formation of new roots (Li et al., 2018). In an experiment where the main root was mechanically stimulated to induce lateral root growth, it was also observed that the expression of WOX5-like genes was activated at different stages of lateral root development, which further suggests that it may play a regulatory role in lateral root development (Baesso et al., 2020). 8.2 Experimental validation through overexpression and knockout Through some genetic experiments, the function of this gene has also been confirmed. Researchers placed PtoWOX5a in the WOX5 mutant of Arabidopsis thaliana and found that it could restore the function of quiescent center (QC) cells in the mutant, indicating that this gene has similar functions in different plants. When PtoWOX5a was overexpressed in poplar trees, both roots and leaves changed: Adventist roots increased, roots became shorter, root tips became larger, leaves became fewer, and leaf area became smaller. These phenomena suggest that PtWOX5 may affect the root development process by regulating genes related to cell division (such as CYCD genes) (Li et al., 2018). In addition, after being stimulated by external pressure, the expression of PtWOX5 during lateral root development also changes, which also supports its role in regulating lateral root formation (Baesso et al., 2020). 8.3 Ecological relevance in reforestation and soil stabilization PtWOX5 regulates root growth and also has practical significance for ecological restoration and soil stabilization and slope protection. It can enhance the formation of advmaturing roots and lateral roots, making poplar trees more likely to take root and expand their root systems more quickly. This is particularly useful in places like degraded land, riverbanks or slopes, as it can help trees fix the soil more quickly and reduce erosion (Li et al., 2018; Baesso et al., 2020). Li et al. (2018) and Baesso et al. (2020) hold that regulating the PtWOX5 gene can provide new ideas and methods for forestry breeding and ecological engineering. 9 Ecological Implications of Root Traits in Populus 9.1 Role of root systems in carbon sequestration The roots of poplar trees can adapt to different soil moisture environments by adjusting the length density, thickness and specific length of the roots. This change is beneficial for it to absorb water and nutrients better, and it can also make the roots grow deeper and more numerous, thereby increasing the weight of the roots. This not only helps trees grow better, but also allows more carbon to remain in the soil, which is very helpful for carbon fixation and storage (Xia et al., 2022; Tan et al., 2023). The roots of poplar trees can also form mutually beneficial relationships with nitrogen-fixing bacteria, mycorrhizal fungi and other microorganisms. These microorganisms are helpful for trees to absorb more nutrients, keep more carbon in the soil and maintain the carbon balance of the entire forest system (Schaefer et al., 2024; Fu et al., 2025). 9.2 Root architecture and soil water conservation The roots of poplar trees make adjustments when the soil is dry (Han, 2024). When the surface is dry, more fine roots will grow deeper into the soil to absorb more water (Tan et al., 2023). The shape and structure of poplar tree roots can also change with the environment, such as increasing the root length or making the root tissue tighter, which is beneficial for more effective water absorption and transportation (Grünhofer et al., 2022; Schaefer et al., 2024). The roots of poplar trees can also work together with microorganisms in the soil to help improve soil structure and enhance soil water retention capacity (Xia et al., 2022; Fu et al., 2025). 9.3 Applications in afforestation and climate-resilient forestry The root systems of different poplar species have different shapes and capabilities. This natural variation provides many options for afforestation and ecological restoration. Selecting varieties with well-developed root systems and strong adaptability can make trees more likely to survive and grow faster, and is suitable for the restoration of
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