A desert endophyte, Priestia megaterium SI1-IITJ, improves fluoride stress tolerance by reducing fluoride content of plant tissues and perturbing salt tolerance and defense genes of Arabidopsis thaliana

We isolated a fluoride (F ^- )-resistant bacterium, Priestia megaterium SI1-IITJ, from thse internal root tissues of several Thar Desert plants, Aerva javanica , Cyperus conglomeratus , Senna tora , and Tephrosia purpurea , tolerating up to 100 mM NaF. The root endophytic behavior of the isolate was confirmed by scanning electron microscopy. SI1-IITJ possesses plant growth-promoting properties, including auxin production (19.8 μg mL ^-1 ), phosphate solubilization (index 3.64), ACC deaminase (0.54 mmol α-ketobutyrate mL ^-1 ) and nitrate reductase (0.65 μmol mL ^-1 nitrite) activities, revealed by biochemical tests and whole genome sequencing. SI1-IITJ extrudes F ^- from the cell, possibly through an F ^- efflux transporter, CrcB , identified in its genome. Significant growth improvements were observed in Arabidopsis thaliana under F ^- stress in hydroponics and soil culture upon coculture with SI1-IITJ, which improved the chlorophyll content by 1.6%, total nitrogen by 30.4%, and reduced reactive oxygen species by 48.9% and F ^- content by 63.9% in plant tissues. A differential gene expression analysis of A. thaliana by transcriptome sequencing indicated an unperturbed F ^- exporter, AtFEX1, but up-regulation of 55 genes regulating root meristem growth, cell wall modification, chlorophyll biosynthesis, Fe homeostasis, and high salt- and abiotic stress-responsive genes. On the other hand, 103 genes were down-regulated, suppressing systemic acquired resistance, plant defense, and H ₂ O ₂ production. In conclusion, our results provide genomic insights into the mechanisms of F ^- toxicity alleviation and plant growth enhancement by a desert PGPR, highlighting Priestia megaterium SI1-IITJ as a potential biofertilizer for mitigating F ^- stress in plants.