Molecular Pathogens, 2025, Vol.16, No.6, 294-302 http://microbescipublisher.com/index.php/mp 296 et al., 2025). The role of ethylene cannot be ignored either. It is somewhat like a coordinator, often working in conjunction with two other hormones to adjust the strength of the immune response. 3.2 Molecular mechanisms of root perception and response to foliar pathogen invasion If the roots can "give an alarm", then the leaves might be the first to get into trouble. Once the leaves are invaded by pathogenic bacteria, the roots can quickly "receive the signal" and then rapidly activate the defense program at the molecular level. At this point, some genes will be upregulated, such as those involved in the metabolism of phenylpropanin, REDOX balance, and the expression of some proteins related to the disease course (Huang, 2025). If beneficial microorganisms happen to be stationed in the rhizosphere, these reactions will be more obvious, and they will further stimulate the expression of key genes in the JA and SA pathways (Boamah et al., 2025). From the perspective of protein level, those disease-resistant wheat will quickly accumulate some defense proteins after the leaves are infected. For example, reactive oxygen species and calcium ion signaling molecules also fluctuate, indicating that the interaction between roots and leaves is not a one-off deal, but a dynamic coordination throughout the entire process. 3.3 Structural, secretory, and immunological changes in roots under pathogen challenge Of course, the changes are not only reflected in signal molecules and gene expression. Some "physical reactions" will also occur at the root itself. Structurally, phenomena such as thickening of cell walls and changes in the types and contents of root secretions are relatively common. This change is not only "outward", but also affects the microbial community around the roots, and thereby affects the entire rhizosphere environment (Zhang et al., 2020). Moreover, when the disease pressure is high, the network of rhizosphere microorganisms will also become more complex. This adjustment is somewhat like a "cooperative model" between plants and microorganisms: you help me identify the pathogen, and I provide the living environment (Liu et al., 2023). These adaptations enable plants to launch more coordinated defenses against pathogens in their leaves or roots, and their overall resistance will also be stronger. 4 Effects of Specific Microbial Inoculants on the Rhizosphere Environment 4.1 Screening, formulation, and colonization potential of microbial additives Not all microbial inoculants are suitable for use in the field. Whether a strain is effective depends not only on whether it is "beneficial" in itself, but also on whether it is "compatible" with the crop. Some bacteria, such as Bacillus, Pseudomonas, Trichoderma, etc., are widely used for screening because they have a relatively obvious promoting effect and strong resistance (Gu et al., 2020). However, merely having the ability to promote growth is not enough. If it cannot stably "take root" in the rhizosphere, it will also be difficult to exert a long-term effect. The study mentioned that under different farming methods and environments, only the microorganisms that successfully colonize can truly help plants grow well and resist adverse conditions (Kampouris et al., 2025). Therefore, when screening and compounding, the adaptability and sustained performance of the strain are often more important than the immediate effect. 4.2 Changes in microbial community structure and functional redundancy in soil After the introduction of microbial agents, some considerable changes will occur in the "native" communities in the soil. Some bacteria are suppressed, while others are "awakened". In particular, groups such as Proteobacteria, Bacteroides, sphingomonas, Pseudomonas tend to increase, and certain Streptomyces or enterobacteriaceae also become more active (Shen et al., 2021). These changes are not entirely bad. Sometimes, they can enhance the functional redundancy of the soil, that is, even if a certain microbiota has problems, the system can still continue to operate (Liu et al., 2025). Of course, the results are not always the same. The source, dosage, formula of the inoculation agent, as well as the type of soil and seasonal changes, will all affect what kind of structure the community will eventually take. 4.3 Enzyme activity and nutrient element dynamics in the rhizosphere When it comes to the nutritional cycle, the enzyme activity in the rhizosphere is an unavoidable topic. The impact of microbial inoculants in this regard is quite direct, especially the effectiveness of key elements such as nitrogen,
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