Plant growth-promoting rhizobacteria (PGPR) are microorganisms that colonize plant roots and enhance plant growth through various mechanisms. These include modifying root architecture, improving plant nutrition, and influencing plant physiology. PGPR can promote plant growth by producing phytohormones, secondary metabolites, and enzymes that affect root development and function. They also enhance plant resistance to pathogens and abiotic stresses, such as heavy metal contamination. PGPR can influence root system architecture by altering the balance of plant hormones like auxin, cytokinin, ethylene, and abscisic acid. These changes can lead to increased lateral root branching, root hair elongation, and improved nutrient uptake. PGPR also modulate plant nutrition through nitrogen fixation, phosphate solubilization, and phytosiderophore production. They can enhance root development and growth by stimulating the production of phytohormones and enzymatic activities, and by facilitating the establishment of rhizobial or mycorrhizal symbioses. PGPR can protect plants through mechanisms such as antagonism of phytopathogens, competition for nutrients, and elicitation of plant defenses like induced systemic resistance (ISR). Some PGPR can also help plants withstand abiotic stresses, including heavy metal contamination. Understanding the molecular mechanisms through which PGPR affect root architecture and plant physiology is crucial for developing sustainable agricultural practices. The impact of PGPR on root system architecture and root structure is influenced by their ability to interfere with plant hormonal balance. PGPR can modulate root development and growth through the production of phytohormones, secondary metabolites, and enzymes. The balance between auxin and cytokinin is a key regulator of plant organogenesis and root architecture. PGPR can affect this balance by producing phytohormones and secondary metabolites that interfere with hormonal pathways. PGPR can also influence plant nutrition through nitrogen fixation, phosphate solubilization, and phytosiderophore production. They can improve root development and growth through the production of phytohormones or enzymatic activities, and by favoring the establishment of rhizobial or mycorrhizal symbioses. PGPR can protect plants through inhibition of phytoparasites, based on antagonism or competition mechanisms, and/or by eliciting plant defenses such as induced systemic resistance (ISR). Some PGPR can also help plants withstand abiotic stresses including contamination by heavy metals or other pollutants. Utilizing PGPR is a new and promising approach for improving the success of phytoremediation of contaminated soils. Understanding and quantifying the impact of PGPR on roots and the whole plant remain challenging. One strategy is to inoculate roots with a PGPR in vitro and monitor the resulting effects on plant. This showed that many PGPR may reduce the growth rate of the primary root, increase the number and/or length of lateral roots, and stimulate root hair elongation in vitro. ConsequentlyPlant growth-promoting rhizobacteria (PGPR) are microorganisms that colonize plant roots and enhance plant growth through various mechanisms. These include modifying root architecture, improving plant nutrition, and influencing plant physiology. PGPR can promote plant growth by producing phytohormones, secondary metabolites, and enzymes that affect root development and function. They also enhance plant resistance to pathogens and abiotic stresses, such as heavy metal contamination. PGPR can influence root system architecture by altering the balance of plant hormones like auxin, cytokinin, ethylene, and abscisic acid. These changes can lead to increased lateral root branching, root hair elongation, and improved nutrient uptake. PGPR also modulate plant nutrition through nitrogen fixation, phosphate solubilization, and phytosiderophore production. They can enhance root development and growth by stimulating the production of phytohormones and enzymatic activities, and by facilitating the establishment of rhizobial or mycorrhizal symbioses. PGPR can protect plants through mechanisms such as antagonism of phytopathogens, competition for nutrients, and elicitation of plant defenses like induced systemic resistance (ISR). Some PGPR can also help plants withstand abiotic stresses, including heavy metal contamination. Understanding the molecular mechanisms through which PGPR affect root architecture and plant physiology is crucial for developing sustainable agricultural practices. The impact of PGPR on root system architecture and root structure is influenced by their ability to interfere with plant hormonal balance. PGPR can modulate root development and growth through the production of phytohormones, secondary metabolites, and enzymes. The balance between auxin and cytokinin is a key regulator of plant organogenesis and root architecture. PGPR can affect this balance by producing phytohormones and secondary metabolites that interfere with hormonal pathways. PGPR can also influence plant nutrition through nitrogen fixation, phosphate solubilization, and phytosiderophore production. They can improve root development and growth through the production of phytohormones or enzymatic activities, and by favoring the establishment of rhizobial or mycorrhizal symbioses. PGPR can protect plants through inhibition of phytoparasites, based on antagonism or competition mechanisms, and/or by eliciting plant defenses such as induced systemic resistance (ISR). Some PGPR can also help plants withstand abiotic stresses including contamination by heavy metals or other pollutants. Utilizing PGPR is a new and promising approach for improving the success of phytoremediation of contaminated soils. Understanding and quantifying the impact of PGPR on roots and the whole plant remain challenging. One strategy is to inoculate roots with a PGPR in vitro and monitor the resulting effects on plant. This showed that many PGPR may reduce the growth rate of the primary root, increase the number and/or length of lateral roots, and stimulate root hair elongation in vitro. Consequently