Functional characterization of a novel plant growth-promoting rhizobacterium enhancing root growth and salt stress tolerance.

Plant growth-promoting rhizobacteria (PGPR) are soil microorganisms through which phytohormones and other bioactive compounds are produced, thereby enhancing plant growth and stress tolerance. In this study, a novel PGPR strain was identified from the rhizosphere of Lycium chinense seedlings, which produce protein-rich fruit. Whole-genome sequencing and annotation revealed that the genome of this strain, designated Pseudomonas sp. A-2, consists of a 6.65-Mb circular chromosome with 5,980 predicted protein-coding sequences. Comparative genomic analysis classified the strain within the genus Pseudomonas. The A-2 strain genome encodes proteins involved in indole-3-acetic acid (IAA) biosynthesis and signaling pathways, which was validated through IAA detection assays and quantitative analyses. Plant growth rates were significantly enhanced by the A-2 strain treatment, with increases of 3-fold in Arabidopsis, 1.5-fold in tobacco, and 1.35-fold in peanut. In Arabidopsis thaliana, expression of key genes associated with lateral and adventitious root formation was induced by the A-2 strain treatment, including ARFs, AMI1, TAA1, YUCs, IBRs, TOB1, and ECH2. Moreover, enhanced tolerance to salt stress was conferred by the A-2 strain treatment, as evidenced by improved biomass accumulation, chlorophyll content, antioxidant enzyme activity, and reduced lipid peroxidation. Levels of total soluble sugars, including trehalose, were elevated in the A-2 strain treated plants, suggesting a role in osmotic adjustment under stress. The plant growth-promoting and stress-alleviating properties of Pseudomonas sp. A-2 highlight its potential application as an effective biological agent for sustainable agriculture.