Emerging Roles of Plant Growth-Promoting Rhizobacteria in Drought Management: Mechanisms and Advanced Strategies for Enhanced Efficiency

Drought represents a major environmental challenge, limiting water availability to plants and disrupting their physiological functions and growth, particularly in dryland regions. Traditional strategies, including water conservation practices, plant breeding, and advanced tools such as genetic engineering, have been employed to enhance drought tolerance. However, these methods are often time-consuming and expensive. Plant growth-promoting bacteria (PGPR) present a promising alternative by forming symbiotic relationships with plant roots and boosting drought resilience. PGPR enhances plant tolerance to drought-induced water stress through complex biochemical and physiological mechanisms, including phytohormone modulation, exopolysaccharides production, nutrient uptake, and gene regulation. Despite these advantages, their performance is often restricted by reduced microbial viability under drought conditions. Recently, nanoencapsulation has emerged as an effective technique in improving PGPR survivability, controlled release, targeted delivery, and root colonization efficiency in semi-arid and arid soils. This review emphasizes the role of PGPR in enhancing drought tolerance by summarizing recent insights on PGPR-mediated drought stress tolerance mechanisms, including phytohormone regulation, antioxidant activity, and osmotic balance. It also explores nanoencapsulation strategies to improve their survival and efficacy under water-limited conditions. Finally, the review highlights the knowledge gaps and future research directions to advance the practical application of PGPR for climate-resilient and sustainable agriculture in dryland regions.