Molecular Microbiology Research 2024, Vol.14, No.5, 236-247 http://microbescipublisher.com/index.php/mmr 237 microorganisms under stresses such as drought, salinity, and disease and its impact on rice stress resistance. It is expected that this review will provide new ideas and methods for improving rice stress resistance, and provide a scientific basis for the application of microbial inoculants and genetic engineering technologies in agricultural practice. 2 Root Physiology and Stress Response of Rice 2.1 Root morphological changes under stress When exposed to various abiotic stresses such as salinity, drought and heavy metals, rice roots undergo significant morphological changes. For example, under salinity, drought and heavy metal stress, rice roots showed changes in root structure, including changes in root length, surface area and volume. These changes are essential to enhance the plant's ability to absorb water and nutrients in the face of adversity (Santos-Medellín et al., 2017; Gupta et al., 2023). Moreover, the presence of beneficial microorganisms in the rhizosphere can further affect root morphology. For example, endophytes and rhizosphere bacteria have been shown to improve root parameters such as root length and root volume under saline-alkali stress (Gupta et al., 2023). 2.2 Physiological adaptation of rice roots to stress Rice roots exhibit multiple physiological adaptations in response to abiotic stresses. A key adaptation is to regulate ion transport to maintain ion homeostasis in plants. For example, under salt stress, rice with mutant SST gene exhibited increased potassium accumulation and decreased sodium accumulation, which is essential for maintaining a stable intracellular environment (Lian et al., 2020). In addition, rice roots can enhance their antioxidant enzyme activities, such as catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD), to alleviate oxidative stress caused by abiotic factors (Jain et al., 2020; Gupta et al., 2023). Under drought stress, root auxin (IAA) and zeatin riboside (ZR) decreased, and the content of cytokinin (CTK) decreased significantly, but the content of abscisic acid (ABA) increased. The reduction of IAA and CTK can reduce the growth rate of the plant and reduce the need for water. Beneficial microorganisms such as Bacillus and Aspergillus can further enhance these physiological responses by stimulating the plant's defense mechanisms (Jain et al., 2020). 2.3 Genetic and molecular basis of root stress response The genetic and molecular basis of rice root stress response involves the regulation of specific genes and signaling pathways. For example, SST genes in rice play a key role in shaping rhizosphere microbial communities and regulating soil metabolites, which in turn affect plant responses to salt stress (Figure 1). Genetic and microbial community analysis revealed significant changes in rhizosphere bacterial communities under salinity stress, which contributes to the improvement of ionic homeostasis in rice plants. Furthermore, potential strategies for using microbial management and genetic modification to enhance crop stress resistance were proposed (Lian et al., 2020). In addition, the expression of stress-responsive genes such as OsPIP1, MnSOD1, and CATa are regulated under salt stress, enhancing the overall stress resistance of plants (Gupta et al., 2023). The recruitment of specific microbial groups by aluminum-tolerant rice genotypes also highlights the genetic basis of root-microbial interactions in enhancing stress tolerance (Xiao et al., 2022). Plant growth-promoting rhizobia (PGPR) and fungi with good characteristics including rhizobia, mycorrhizal fungi, and trichoderma, which have been successfully applied in agriculture to enhance nutrient absorption, fight pathogens, and promote growth (Genre et al., 2020; Yang et al., 2022; Woo et al., 2023). In addition, the presence of arbuscular mycorrhizal fungi (AMFs) can affect gene expression associated with nutrient uptake and stress resistance, thereby improving plant resistance to heavy metal stress (Hao et al., 2021). 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 phytoantitoxin and lignin, thereby inhibiting the growth and reproduction of pathogenic bacteria (Chen et al., 2021). Figure 1 from Lian et al. (2020) provides a detailed analysis of the genetic and molecular basis of root stress responses, focusing on the rhizosphere microbial community under different SST gene variations and stress
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