Recent Advances on PGPR, Beneficial Fungi, and Nanoparticles in Plant Abiotic Stress Tolerance: Current Evidence, Emerging Interactions, and Research Gaps

Various abiotic challenges, including severe drought, extreme temperatures, salinity, and heavy metal toxicity, substantially limit plant growth and agricultural sustainability on a global scale. Sustainable approaches that strengthen crop resilience while minimizing environmental impacts are therefore urgently needed. Plant growth-promoting rhizobacteria (PGPR), beneficial fungi, and nanoparticles have individually demonstrated considerable potential in improving plant growth, nutrient acquisition, antioxidant defense, and stress tolerance. PGPR enhance plant performance through phytohormone production, nutrient solubilization, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, and activation of systemic defense responses. Beneficial fungi augment water uptake, nutrient absorption, osmotic adjustment, and stress-responsive signaling pathways, whereas nanoparticles facilitate efficient nutrient delivery, enhance photosynthetic performance, and support plant adaptation under adverse environmental conditions. Recent studies have further highlighted the synergistic benefits of PGPR–fungi, fungi–nanoparticle, and PGPR–nanoparticle interactions in mitigating abiotic stress. However, integrated tripartite interactions among PGPR, beneficial fungi, and nanoparticles remain insufficiently explored. This review summarizes current knowledge regarding their individual and combined roles, discusses the underlying physiological and molecular mechanisms, identifies existing research gaps, and proposes future perspectives for developing climate-resilient sustainable agricultural systems.