Molecular pathways in plant growth-promoting rhizobacteria-plant interactions: a comprehensive review

Plant growth-promoting rhizobacteria (PGPR) enhance plant growth, nutrient uptake and tolerance to biotic and abiotic stress through diverse microbial traits and plant-associated responses. At the molecular level, PGPR influences plant physiology by modulating phytohormone balance, nutrient signaling, and defense-related pathways. This review summarizes current knowledge on bacterial traits involved in nitrogen fixation, phytohormone production and modulation, siderophore-mediated iron acquisition and induced systemic resistance with an emphasis on molecular components and regulatory frameworks that have been experimentally characterized. Key signaling elements including reactive oxygen species, calcium fluxes, mitogen-activated protein kinase cascades, and hormone-responsive transcriptional regulators such as NPR1, are highlighted as central nodes in PGPR-associated plant responses. Where direct molecular causality remains unresolved, plant phenotypes observed are presented as evidence-based associations, and remaining knowledge gaps are identified. By integrating molecular components with functional outcomes, this review provides a conceptual framework for understanding how microbial traits interface with plant signaling networks and identifies priorities for future mechanistic research.