Sadhukhan, Ayan

Aims: This study aimed to isolate plant growth and drought tolerance-promoting bacteria from the nutrient-poor rhizosphere soil of Thar desert plants and unravel their molecular mechanisms of plant growth promotion. Methods and results: Among our rhizobacterial isolates, Enterobacter cloacae C1P-IITJ, Kalamiella piersonii J4-IITJ, and Peribacillus frigoritolerans T7-IITJ, significantly enhanced root and shoot growth (4 - 5-fold) in Arabidopsis thaliana under PEG-induced drought stress. Whole genome sequencing and biochemical analyses of the non-pathogenic bacterium T7-IITJ revealed its plant growth-promoting traits, viz., solubilization of phosphate (40-73 μg/ml), iron (24 ± 0.58 mm halo on chrome azurol S media), and nitrate (1.58 ± 0.01 μg/ml nitrite), along with production of exopolysaccharides (125 ± 20 μg/ml) and auxin-like compounds (42.6 ± 0.05 μg/ml). Transcriptome analysis of A. thaliana inoculated with T7-IITJ and exposure to drought revealed the induction of 445 plant genes (log2fold-change > 1, FDR < 0.05) for photosynthesis, auxin and jasmonate signalling, nutrient uptake, redox homeostasis, and secondary metabolite biosynthesis pathways related to beneficial bacteria-plant interaction, but repression of 503 genes (log2fold-change < -1) including many stress-responsive genes. T7-IITJ enhanced proline 2.5-fold, chlorophyll 2.5 - 2.8-fold, iron 2-fold, phosphate 1.6-fold, and nitrogen 4-fold, and reduced reactive oxygen species 2 - 4.7-fold in plant tissues under drought. T7-IITJ also improved the germination and seedling growth of Tephrosia purpurea, Triticum aestivum, and Setaria italica under drought and inhibited the growth of two plant pathogenic fungi, Fusarium oxysporum, and Rhizoctonia solani. Conclusions: P. frigoritolerans T7-IITJ is a potent biofertilizer that regulates plant genes to promote growth and drought tolerance.