RL-WG26 mediated salt stress tolerance in rice seedlings: A new insight into molecular mechanisms

Soil salinization has significant deleterious impacts on arable lands and crop productivity worldwide. Plant growth-promoting rhizobacteria (PGPR) have the capability to establish mutualistic associations with plants, resulting in the increase of plant growth under abiotic stress. PGPR strain RL-WG26 was previously isolated from the rhizosphere of rice Sea Rice 86 (SR86). In this study, by genome-based average nucleotide identity (ANI) calculation, RL-WG26 was re-identified as Pseudomonas promysalinigenes here instead of Pseudomonas putida. SR86 seedlings inoculated with RL-WG26 possessed significant increases in plant biomass (fresh weight and dry weight), root surface area and length, and chlorophyll content under either normal or saline conditions, when compared with those without RL-WG26 inoculation. Ion content analysis demonstrated that seedlings inoculated with RL-WG26 contained lower Na+ and Cl- accumulation but higher K+ and Ca2+ uptake under saline condition, which finally alleviated the salt ion toxic in the RL-WG26 inoculated seedlings, when compared with those without RL-WG26 inoculation. In addition, SR86 seedlings inoculated with RL-WG26 also exhibited higher antioxidant activity and higher concentration of osmoregulation factor proline than those without RL-WG26 inoculation. At last, genomic analysis of strain RL-WG26 identified several genes and gene clusters encoding 1-aminocyclopropane-1-carboxylic acid (ACC)-deaminase, the tryptophan-dependent indole-3-acetic acid (IAA) synthesis pathway, and the synthesis of betaine. Taken together, PGPR strain RL-WG26 could enhance the growth and salt stress tolerance in SR86 seedlings through various pathways, which provide a foundation for deciphering the molecular mechanisms of strain RL-WG26-mediated plant salt tolerance and promote the application of this strain.