Molecular Mechanisms of Plant Growth–Promoting Rhizobacteria (PGPR) in Biofertilization and Disease Suppression of Crops

Abstract

Plant growth–promoting rhizobacteria (PGPR) are beneficial soil bacteria that colonize the rhizosphere and enhance plant growth through direct and indirect mechanisms, including nutrient solubilization, phytohormone production, suppression of phytopathogens, and activation of plant defense mechanisms. PGPR-based techniques are gaining popularity in sustainable agriculture as environmentally friendly alternatives to chemical fertilizers and insecticides. Although PGPR have been extensively studied, the molecular mechanisms behind these beneficial interactions are still dispersed throughout the literature. Recent advances in molecular biology and high-throughput omics technology have rapidly expanded the identification of genes, pathways, and regulatory networks associated with PGPR activities. However, these findings are often reported in isolation, and a consolidated and integrative synthesis of molecular mechanistic insights is lacking, restricting a system-level knowledge of PGPR–plant interactions and impeding the rational development of effective bioinoculant formulations. Therefore, a comprehensive review is required to consolidate current understanding and elucidate how molecular pathways support PGPR-mediated plant growth promotion and biocontrol. This review aims to provide an updated synthesis of molecular mechanisms governing PGPR-mediated biofertilization and biocontrol. The main mechanisms discussed are microbial-driven nutrient solubilization and mobilization, phytohormone biosynthesis and signaling, secretion of antimicrobial metabolites and lytic enzymes, and induction of plant systemic resistance pathways. The emphasis is on how these molecular mechanisms combine and work together to promote plant growth, stress tolerance, and disease resistance. This review emphasizes the functional diversity of PGPR and their potential application in next-generation biofertilizers and biopesticides by incorporating new genomic and molecular findings. A clearer mechanistic framework will help to build more consistent and efficient PGPR-based technologies, reducing reliance on synthetic agrochemicals and improving soil health and crop production systems.