Molecular Microbiology Research 2024, Vol.14, No.5, 236-247 http://microbescipublisher.com/index.php/mmr 242 4.3 Synergistic effects of root-microbial interactions against adversity The synergy between rice roots and rhizosphere microorganisms plays a key role in enhancing plant stress resistance. These interactions can improve nutrient access, promote root growth, and enhance resistance to environmental stresses. For example, the presence of specific microbial communities in the rhizosphere can mitigate the negative effects of salinity on rice by regulating soil metabolites and microbial community structure (Lian et al., 2020, Santos et al., 2021). In addition, combined inoculation of PGPR and mycorrhizal fungi has been shown to have a cumulative effect on plant growth and stress resistance, highlighting the importance of microbial synergies in sustainable agriculture (Nadeem et al., 2014). In addition, the root system can secrete malic acid, which is an effective chemotant of Bacillus subtilis, which is a rhizosphere growth-promoting bacterium that activates the secretion of osmotic substances to enhance drought resistance, while interacting with other rhizosphere bacteria to enhance the plant's ability to resist drought. These microorganisms are able to produce antioxidants and other stress-related compounds that further enhance the resilience of plants under adverse conditions (Gupta et al., 2023). 5 Case Studies and Experimental Evidence 5.1 Drought stress tolerance through root-microbe synergy Several studies have demonstrated the root-related microorganisms play an important role in improving drought stress tolerance in rice. For instance, a consortium of rhizobacteria, Bacillus amyloliquefaciens Bk7 and Brevibacillus laterosporus B4, along with biochemical elicitors such as salicylic acid and β-aminobutyric acid, was shown to improve drought tolerance in rice plants. The treated plants exhibited 100% survival after 16 days without water, with notable improvements in seedling height, shoot number, and reduced symptoms of chlorosis, wilting, and necrosis. The mechanisms underlying this enhanced tolerance included increased activities of antioxidant enzymes and up-regulation of stress-responsive genes (Kakar et al., 2016). Another study highlights the role of drought-tolerant PGPR isolated from drought-tolerant rice genotypes. These PGPRs are associated with increased soil enzyme activities and improved growth status under drought conditions. The inoculation of drought-sensitive rice genotypes with these PGPRs leds to the up-regulation of several growth and stress-responsive genes, thereby enhancing drought tolerance (Omar et al., 2021). Additionally, research on the restructuring of rice root-associated microbiomes under drought stress revealed significant changes in microbial composition, with an enrichment of drought-responsive taxa that potentially contribute to plant survival under extreme conditions (Santos-Medellín et al., 2021). 5.2 Alleviate salt stress through rhizosphere microbial support The alleviation of salt stress in rice through rhizosphere microbial support is also widely studied. An experiment tested the effects of endophytic and rhizosphere microorganisms on two rice varieties under high salt conditions. The results showed that these microorganisms improved the photosynthesis apparatus and induced antioxidant enzyme activity, leading to better salt stress tolerance (Figure 3). The regulation of the expression of salt stress-responsive genes and the improvement of root structure parameters were also observed (Gupta et al., 2023). Bacillus subtilis GB03 strain stimulated the expression of HKTI gene in Arabidopsis thaliana buds, and under salt stress (100mmo1/LNaC), the GB03 strain down-regulated the expression of HKT1 gene in roots and up-regulated buds, respectively, resulting in lower Na* accumulation in the whole plant than in the control. Piriformospora indica, on the other hand, colonized Arabidopsis roots under salt stress and showed enhanced expression of HKT1 gene in rice. In addition, AMF is also involved in the regulation of specific metabolic pathways in the root system of host plants, promoting the synthesis and secretion of terpenes and phenolic compounds, as well as the deposition of resistant substances such as phytoalexin and lignin, thereby inhibiting the growth and reproduction of pathogenic bacteria (Chen et al., 2021a). Further studies of microbiota from specific environments have demonstrated that these microbiotas can enhance rice tolerance to salinity. Inoculation of paddy fields and salt-tolerant microbiotas led to an increase in stem and
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