Molecular Pathogens, 2025, Vol.16, No.5, 217-225 http://microbescipublisher.com/index.php/mp 220 promote root development or change nutrient absorption patterns. Pattern molecules such as flagellin and fungal cell wall fragments of pathogenic microorganisms are recognized by plants, triggering a burst of reactive oxygen species in roots and activation of defense enzymes, and initiating local immune responses. On the other hand, symbiotic microorganisms such as mycorrhizal fungi release special signals that reduce plant defense responses to facilitate the establishment of symbiosis. Volatile organic compounds produced by some growth-promoting bacteria can induce systemic resistance (ISR) in plants and improve the resistance of the entire plant to diseases and stress (Saleh et al., 2023). 4.3 Bidirectional control mechanism There is a two-way feedback regulation between wheat roots and rhizosphere microorganisms. After beneficial bacteria colonize, plants increase root exudates to provide carbon sources and promote the prosperity of the bacterial community; microbial nitrogen fixation, phosphorus decomposition and other activities increase the supply of nutrients in the rhizosphere, which in turn affects plant nutrient absorption strategies and strengthens the mutualistic relationship (Bharti et al., 2022; Parunandi et al., 2023). On the contrary, when pathogenic bacteria invade, wheat will adjust the composition of secretions (such as increasing antibacterial substances and reducing carbon sources that can be used by pathogens) to inhibit the growth of pathogens and facilitate the expansion of antagonistic bacteria, jointly suppressing the disease. Plants can also secrete interfering molecules that block the quorum sensing of harmful bacteria and prevent their excessive reproduction. Through these two-way regulatory mechanisms, the rhizosphere system maintains a dynamic balance in which beneficial interactions dominate. 5 Case Study: Study on the Interaction Mechanism of Wheat-Bacillus 5.1 Experimental design and strain screening Bacteria of the genus Bacillus are often used as model microorganisms to study growth-promoting interactions in wheat. Usually, multiple Bacillus strains are isolated from wheat rhizosphere soil, and strains with stronger growth-promoting and antagonistic activities are screened for testing. The strains obtained by screening were made into a bacterial suspension, and wheat seedlings were inoculated under greenhouse pot conditions. No inoculation was used as a control. Growth indicators such as plant height, root length, dry weight, and disease occurrence were measured regularly to evaluate the growth promotion and biocontrol effects of the strains. At the same time, by marking strains and regularly detecting the number of rhizosphere bacteria, the colonization ability and dynamic changes of this Bacillus in wheat roots can be understood. 5.2 Interaction mechanism and molecular characteristics Bacillus has various mechanisms to promote wheat growth and prevent diseases. It can form biofilm on the surface of wheat roots, helping strains to adhere and colonize for a long time. Secondly, in terms of growth promotion, Bacillus produces phytohormones such as IAA to stimulate root elongation and branching (Azaroual et al., 2020), secretes organic acids and enzymes to increase the availability of nutrients such as phosphorus in the soil, and has ACC deaminase activity, which can reduce plant ethylene levels and alleviate adverse stress. Thirdly, in terms of biocontrol, it synthesizes antibiotic substances such as cyclic lipopeptides to inhibit pathogenic fungi, and can induce systemic resistance (ISR) in wheat through certain molecules and improve the plant's own defense capabilities (Figure 2) (Rumyantsev et al., 2023). Research shows that after wheat is inoculated with Bacillus, the activity of root defense enzymes increases and the expression of growth-related genes is enhanced; Bacillus also upregulates secondary metabolism, movement and other related genes in the presence of plants, reflecting that plant signals can activate the interactive response of strains. 5.3 Application prospects and challenges The interaction between wheat and Bacillus shows good application prospects. Many Bacillus inoculants have been tested on wheat and have achieved results, such as promoting nutrient absorption, increasing yields, and reducing the incidence of root diseases. They are expected to partially replace chemical fertilizers and pesticides. At the same time, its large-scale promotion also faces challenges: under different soil and climate conditions, the effect of bacterial agents often fluctuates, and it is difficult for some exogenous bacteria to stably colonize and
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