Molecular Microbiology Research 2024, Vol.14, No.4, 171-180 http://microbescipublisher.com/index.php/mmr 173 for initiating symbiosis (Rasmann and Turlings, 2016). The ability of microbes to sense and respond to these signals is critical for their colonization and interaction with plant roots, ultimately influencing plant growth and health. 3.1.3 Mutual recognition and binding processes The mutual recognition and binding processes between trees and their microbial symbionts involve a series of molecular interactions that ensure compatibility and successful symbiosis. These processes often begin with the recognition of root exudates by microbial receptors, followed by the activation of signaling pathways that lead to the expression of symbiosis-related genes. For instance, the establishment of AM symbiosis involves the activation of an ancestral signaling pathway in plants, which is also utilized for legume-rhizobia symbiosis (Figure 1) (Wang et al., 2020). This pathway facilitates the formation of specialized structures, such as arbuscules and nodules, where nutrient exchange occurs. The mutual recognition and binding are essential for the formation of a stable and functional symbiotic relationship. The study by Wang et al. (2020) demonstrated how arbuscular mycorrhizal (AM) symbiosis promotes the legume-rhizobium symbiosis by regulating the rhizosphere microbial community, and revealed the regulatory role of plant genotype in this symbiotic relationship. This process provides nutrients to the plants and enhances their growth and ecological functions. 3.2 Molecular pathways of symbiosis formation The formation of symbiotic relationships between trees and microbes involves complex molecular pathways that regulate the development and maintenance of these interactions. These pathways include the perception of microbial signals by plant receptors, the activation of downstream signaling cascades, and the expression of genes involved in symbiosis. For example, the establishment of AM symbiosis requires the activation of a common symbiosis signaling pathway, which involves the perception of fungal signals by plant receptors and the subsequent activation of calcium signaling and transcriptional responses. Similarly, the formation of legume-rhizobia symbiosis involves the recognition of rhizobial Nod factors by plant receptors, leading to the activation of signaling pathways that promote nodule formation and nitrogen fixation (Tsiknia et al., 2020; Wang et al., 2020). 3.3 Genetic basis of symbiotic compatibility The genetic basis of symbiotic compatibility between trees and their microbial symbionts is determined by the presence of specific genes that regulate the recognition, signaling, and development of symbiotic structures. These genes are often conserved across different plant species and are essential for the establishment of symbiosis. For instance, genes involved in the common symbiosis signaling pathway, such as those encoding receptor-like kinases and calcium-dependent protein kinases, are required for both AM and legume-rhizobia symbioses. Additionally, genetic variation in both plants and microbes can influence the efficiency and stability of symbiotic interactions, highlighting the importance of genetic compatibility for successful symbiosis (Lagunas et al., 2015). Understanding the genetic basis of symbiotic compatibility can inform strategies for improving plant-microbe interactions in agricultural and ecological contexts. 4 Ecological Functions of Symbiotic Microbes 4.1 Nutrient acquisition and recycling Symbiotic microbes play a crucial role in nutrient acquisition and recycling within the rhizosphere. Mycorrhizal fungi and nitrogen-fixing bacteria are particularly significant in this context. These microbes enhance plant mineral nutrition by converting unavailable nutrients into forms that plants can absorb. For instance, plant growth-promoting rhizobacteria (PGPR) convert essential nutrients like nitrogen, phosphorus, and zinc into available forms, thereby improving soil fertility and plant growth (Jacoby et al., 2017; Huang, 2024). The interaction between soil microbes and plants significantly affects soil microbial structure and function, which in
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