Mechanisms of microbial regulation in plant responses to salt stress

Salinity stress is one of the most severe abiotic stresses threatening global agricultural production, impairing crop yield and quality through multiple mechanisms including disruption of soil water balance, induction of ion toxicity, oxidative damage, and competition for nutrient elements. As core members of the plant microbiome, plant growth-promoting rhizobacteria (PGPRs) and plant growth-promoting endophytes (PGPEs) have been extensively studied in recent years for their molecular mechanisms in regulating plant salt stress resistance. This article systematically reviews the key mechanisms by which PGPRs and PGPEs enhance plant salt tolerance through multidimensional interactions: Firstly, microbes modulate plant auxin signaling pathways, gibberellin-mediated cell elongation, and abscisic acid-induced stomatal responses by synthesizing plant hormones, thereby alleviating physiological inhibition caused by salinity stress. Secondly, through secretion of antioxidant enzymes and non-enzymatic antioxidants, microbes effectively scavenge reactive oxygen species (ROS), mitigate oxidative damage, and maintain cellular metabolic homeostasis. Thirdly, microbes regulate the expression of ion transport proteins to promote Na⁺ efflux and K⁺/Ca²⁺ uptake, optimize K⁺/Na⁺ equilibrium, and reduce ion toxicity. Additionally, microbial exopolysaccharides (EPS) provide synergistic protection by chelating Na⁺ and improving rhizosphere microenvironment, while volatile organic compounds (VOCs) modulate photosynthetic efficiency, osmotic balance, and systemic resistance. Notably, endophytic fungi can activate mitogen-activated protein kinase (MAPK) signaling pathways and the high osmolarity glycerol (HOG-MAPK) pathway, inducing phosphorylation of transcription factors and upregulating stress-responsive genes to achieve epigenetic regulation and metabolic reprogramming. Although previous studies demonstrate that microbes enhance plant adaptability through regulation of root architecture, nitrogen/phosphorus metabolism, and signaling molecules, the molecular mechanisms of microbe-derived signal peptides (SPMs) and VOCs in salt stress responses remain unclear-particularly how they regulate plant hormone synthesis or interact with pattern recognition receptor (PRR) signaling pathways via long-distance signaling. Future research should integrate multi-omics technologies to decipher the complex network of microbe-plant interactions, develop salt tolerance enhancement strategies using synthetic microbial communities, and explore the potential of SPMs and VOCs as biosensors or precision agriculture tools. This review aims to provide theoretical foundations and practical directions for microbiome resource utilization in saline-alkali agriculture, salt-resistant crop variety improvement, and intelligent environmental monitoring technologies.