Tree Genetics and Molecular Breeding 2025, Vol.15, No.3, 117-127 http://genbreedpublisher.com/index.php/tgmb 121 when the roots of poplar trees interact with arbuscular mycorrhizal (AM) fungi, certain specific genes are activated. These genes are related to processes such as nutrient transport, signal transmission and immune defense. Fröschel et al. (2020) discovered through genomic and proteomic studies that during the symbiotic process of plants, they adjust gene expression in different cellular layers to assist in fungal colonization and nutrient exchange, and also regulate defense responses to prevent excessive immunity. 6.2 Rhizosphere microbiome shaping by root exudates Different poplar genotypes release different organic acids, sugars and secondary metabolites, which can attract beneficial bacteria while rejecting harmful ones. Demiwal et al. (2024) also found through transcriptome and metabolome analysis that root secretions can regulate the behavior of microorganisms, such as enabling them to express genes related to colonization, nutrient absorption, and signal recognition. The types and quantities of these secretions are controlled not only by the genes of the poplar itself but also by the surrounding environment (Yu and Hochholdinger, 2018). 6.3 Genomic response to beneficial and pathogenic microbes When the roots of poplar trees come into contact with different types of microorganisms, such as beneficial probiotes or fungi, or harmful pathogens and nematodes, it activates different gene expression networks. Research has found that different cellular layers respond differently to microorganisms. For instance, outer cells are more likely to activate defense genes to fight against pathogenic bacteria; The inner cells mainly activate some genes related to symbiosis (Figure 2) (Fröschel et al., 2020). Furthermore, plants also adjust hormone signals and metabolic processes, promoting the activities of beneficial bacteria on the one hand and suppressing pathogens on the other hand (Demiwal et al., 2024). Genomic association analysis also indicates that the genetic background of plants can affect the types and functions of microorganisms around the roots (Wille et al., 2018; He et al., 2021; Martinez, 2023). These results have significant reference value for future genetic improvement and enhancing the cooperative ability between plants and microorganisms. 7 Root Plasticity and Environmental Responses 7.1 Root adaptation to drought, flooding, and nutrient limitation The root system of poplar trees is very flexible and can adjust its structure and distribution pattern according to changes in the environment. Populus euphratica seedlings grow adventite roots when there is drought or too much water to help maintain stability and obtain oxygen. When the water level deepens, they also increase the number and length of their roots to adapt to the changes in moisture (Wang et al., 2021). Different soil environments can also cause changes in the morphology of root systems. When there is less clay water, the roots will work harder to grow outward. In sandy soil, to absorb more water and nutrients, roots will increase their total length. The roots of poplar trees also adjust the rate of formation and death of fine roots according to the amount of water and nutrients in the soil, especially during the growing season. This “transformable” ability enables poplar trees to maintain normal growth when facing drought, flooding or nutrient deficiency. 7.2 Epigenetic and transcriptional regulation under abiotic stress When the root system of poplar trees encounters abiotic stress, it will adapt to these problems through genetic regulation. Transcriptome analysis revealed that under different water conditions, the expression levels of many genes in roots would increase or decrease. These genes are related to antioxidation, cell protection, cell wall adjustment, etc. Xu et al. (2021) found that the gene XET is “activated” by drought, and its promoter contains sequences responding to drought. After overexpression of this gene, the drought resistance of roots will be enhanced. There are also modules like miR476a-RFL that regulate mitochondrial function and auxin signaling, thereby promoting the formation of adventitious roots. Genomic and QTL studies have also identified key loci that control root morphology and function, indicating that these characteristics are jointly regulated by genetics and epigenetics (Liang et al., 2024).
RkJQdWJsaXNoZXIy MjQ4ODYzNA==