Pseudomonas sp. Strain ADAl3–4 Enhances Aluminum Tolerance in Alfalfa (Medicago sativa)

Aluminum toxicity severely inhibits root elongation and nutrient uptake, causing global agricultural yield losses. Dissolved Al³⁺ are accumulating in plants and subsequently entering food chains via crops and forage plants. Chronic dietary exposure to Al³⁺ poses a risk to human health. In this study, <i>Pseudomonas</i> sp. strain ADAl3-4, isolated from plant rhizosphere soil, significantly enhanced plant development and biomass. Phenotypic validation using <i>Arabidopsis</i> mutants showed that strain ADAl3-4 regulates plant growth and development under aluminum stress by reprogramming the cell cycle, regulating auxin and ion homeostasis, and enhancing the root absorption of Al³⁺ from the soil. Transcriptomic and biochemical analyses showed that strain ADAl3-4 promotes plant growth via regulating signal transduction, phytohormone biosynthesis, flavonoid biosynthesis, and antioxidant capacity, etc., under aluminum stress. Our findings indicate that <i>Pseudomonas</i> sp. strain ADAl3-4 enhances plant development and stress resilience under Al³⁺ toxicity through a coordinated multi-dimensional regulatory network. Furthermore, strain ADAl3-4 promoted the root absorption of aluminum rather than the transportation of Al to the aerial part, endowing it with application prospects.