Multidimensional Analysis of Rice Plant–Microbe Interactions Under Saline Stress

Plant–microbe interactions are dynamic and complex processes. The positive influence of rhizobacterial strains enables crops to alleviate stress and enhance growth. This study directly investigates the effect of the rhizobacterial strain PK7 (Pseudomonas taiwanensis-Accession no. MT218377) on growth promotion and stress tolerance in salt-tolerant and susceptible varieties of rice seedlings. Seed priming with PK7 increased the germination rate (200%) for salt-susceptible rice variety UMA and for 125% increment for salt-tolerant variety VTL 11 at 150 mM salt stress. Additionally, PK7 treatment modified root morphology, resulting to increased root length, number of roots, and root hairs. Anatomical changes were also observed in plants treated with PK7. The activity of antioxidant enzymes, including catalase, ascorbate peroxidase, guaiacol peroxidase, and superoxide dismutase was increased by 7.5, 3, 46.5 and 4.7 times respectively in PK7 inoculated seedlings. Root metabolite profiling of the salt-susceptible rice variety UMA was performed using high-resolution liquid chromatography-mass spectrometry (HRLCMS). This analysis revealed distinct patterns of metabolite modulation in rice roots under both salt stress and normal conditions. The most prominent compound identified was choline, a crucial precursor to glycine betaine (GB) and phospholipids. Choline plays a pivotal role in enhancing a plant’s tolerance to salt stress. Additionally, significant compounds like proline and sphingosine were also detected. Furthermore, the study ascertained the accumulation of sugars, particularly 27% of galactose in seedlings treated with PK7 under stress condition. These findings suggest a novel stress-alleviating mechanism mediated by enhanced root metabolites.