Abstract
Global climate change intensifies heat stress, posing a severe threat to agricultural productivity and food security. Employing stress-tolerant plant growth-promoting microorganisms (PGPM), particularly growth-promoting rhizobacteria (PGPR), has emerged as a promising and sustainable strategy to enhance crop thermotolerance. This review emphasizes thermotolerant PGPR and integrates the roles of fungal endophytes, mycorrhizal fungi, and archaea. These beneficial root-colonizing microorganisms mitigate heat stress through multifaceted mechanisms, including nutrient solubilization, phytohormone production, modulation of antioxidants, and activation of stress-responsive genes. This comprehensive review consolidates existing research on the physiological, biochemical, and molecular effects of heat stress on plants and clarifies the primary mechanisms by which PGPR enhance resistance, supplemented with summary tables and schematic models. We discuss how microbial traits, including exopolysaccharide production, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, heat shock proteins, antioxidant systems, and siderophore synthesis, contribute to improved plant growth, photosynthetic efficiency, and reproductive success under high temperatures. Integrating microbial biotechnology with conventional agronomy has significant potential to develop climate-resilient cropping systems. Future research should prioritize identifying robust microbial strains for diverse agro-climatic zones and unraveling signaling networks underlying plant-microbe interactions.