Molecular Pathogens, 2025, Vol.16, No.5, 246-256 http://microbescipublisher.com/index.php/mp 250 microbial interactions. Under different conditions such as sufficient water, drought, soil salinity, etc., the amount and composition of wheat root exudates will change significantly, thereby regulating the rhizosphere microbial community to adapt to stress. Under salt stress conditions, high-salt environments can cause osmotic stress and ion toxicity to plants and microorganisms. Research shows that salt-tolerant rhizosphere growth-promoting bacteria can use substances such as glycerol and sugar secreted by plants to enhance their own salt resistance and continue to provide growth assistance to plants. Under water stress (drought) conditions, plants such as wheat often stabilize the rhizosphere microbiota and improve drought resistance by changing root secretion (Cherif-Silini et al., 2019; Ateş et al., 2020). On the one hand, drought will cause the rhizosphere soil water film to become thinner, reduce the diffusion range of nutrients and secretions, and increase their concentration, which may intensify competition among microorganisms. On the other hand, under drought stress, plant roots will also secrete some signaling molecules to stimulate microorganisms to assist in drought resistance. For example, there is experimental evidence that plants secrete increased ethylene precursor (ACC) during drought, promoting the proliferation of bacteria containing ACC deaminase in the rhizosphere. These bacteria degrade ACC and reduce ethylene accumulation in plants, thereby alleviating the suppression of root systems by drought (Sorty et al., 2023). 5.3 Root exudates regulate microbiota stability under drought conditions Drought is one of the major stresses affecting wheat yield and soil ecological balance. Under sustained drought conditions, wheat root exudates play a key role in maintaining the stability of the rhizosphere microbiota. Drought will reduce the number and diversity of some rhizosphere microorganisms, but some specific bacterial groups are also enriched under drought (Usyskin-Tonne et al., 2021). Under drought conditions, wheat roots secrete large amounts of polysaccharide mucus and polymers. These substances can promote the formation of soil microaggregates and increase soil water retention, creating a moist microenvironment to buffer external drought. Rhizosphere mucus can also be used as a carbon source to maintain the basic metabolism of microorganisms and prevent the collapse of beneficial bacteria due to carbon deficiency (Lang et al., 2025). Drought triggers plant metabolic reprogramming, and wheat roots may release some signaling metabolites to stabilize the network structure of the microbiota. Recent research proposes the phenomenon of “systemically induced root secretion” (SIREM), that is, plants regulate the secretion of specific metabolites in non-stressed parts by roots through root-root signaling under stress (Höfte, 2020). Microorganisms themselves are also involved in establishing drought-resistant homeostasis. Certain growth-promoting bacteria in the wheat rhizosphere can produce extracellular polymers (EPS) and plant hormones, and drought will induce wheat to release signals to stimulate these bacteria to increase EPS production and hormone secretion, thereby providing feedback to improve plant drought resistance. 6 Symbiosis Mechanism between Root Exudates and Microorganisms Related to Wheat Growth Promotion 6.1 Colonization mechanism of nitrogen-fixing bacteria and phosphate-solubilizing bacteria Although wheat itself does not form a nodule symbiosis like the legumes, its rhizosphere maintains a close mutualistic relationship with a series of autogenic nitrogen-fixing bacteria and phosphorus-solubilizing bacteria. In terms of nitrogen-fixing bacteria, some bacteria that can autogenously fix nitrogen are common in the wheat rhizosphere, such as Azospirillum, Azotobacter, etc. They provide additional nitrogen to the wheat, which in turn supplies carbon through root exudates to sustain its growth. This mutualistic symbiosis first relies on the chemotactic attraction of root exudates. Studies have shown that the organic acids and sugars secreted by wheat roots have a strong chemotactic effect on Fasciform bacteria, allowing them to move toward the root surface along the concentration gradient and colonize (O’Neal et al., 2019). When nitrogen-fixing bacteria reach the rhizosphere, certain phenolic substances secreted by the roots can also induce the expression of nitrogen-fixing genes and increase their nitrogenase activity. In terms of phosphate-solubilizing bacteria, there are a variety of bacteria in the wheat rhizosphere that convert insoluble phosphorus in the soil into plant-usable forms by secreting organic acids and enzymes. The carbon
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