Halotolerant bacterial endophyte Bacillus velezensis CBE mediates abiotic stress tolerance with minimal transcriptional modifications in Brachypodium distachyon

Nitrogen and water are the primary resources limiting agricultural production worldwide. We have demonstrated the ability of a novel halotolerant bacterial endophyte, <i>Bacillus velezensi</i>s CBE, to induce osmotic stress tolerance in <i>Brachypodium distachyon</i> under nitrogen-deprived conditions. Additionally, we aimed to identify the molecular factors in plants that contribute to the beneficial effects induced by <i>B. velezensis</i> CBE in <i>B. distachyon</i>. To achieve this, we conducted transcriptomic profiling using RNA-seq on 18-day-old <i>B. distachyon</i> seedlings treated with <i>B. velezensis</i> CBE in the presence or absence of available nitrogen, with and without osmotic stress. These profiles were then compared to those obtained from <i>B. distachyon</i> treated with known plant growth-promoting bacterial strains, <i>Azospirillum brasilense</i> Cd and <i>Azoarcus olearius</i> DQS4, under the same growth conditions. We identified differentially expressed genes (DEGs) in response to the combinations of bacterial strains and stress treatments. Interestingly, only 73 transcripts showed significant differential expression in <i>B. velezensis</i> CBE-treated plants under stress conditions, compared to 1,078 DEGs in plants treated with <i>A. brasilense</i> Cd and 2,015 DEGs in <i>A. olearius</i> DQS4. Our findings suggest that the novel endophyte <i>B. velezensis</i> CBE mediates osmotic stress tolerance in <i>B. distachyon</i> through the fine-tuning of molecular mechanisms with minimal transcriptional modifications.