Priming of resistance against Pseudomonas syringae pv. tomato in Arabidopsis by volatiles of Bacillus subtilis

Microbial volatiles have an important role in plant growth promotion and protecting them against plant pathogens. In this work, we evaluated whether B. subtilis volatiles promote plant growth and induce resistance against P. syringae pv. tomato DC3000. Arabidopsis seedlings exposed to bacterial volatiles in two compartments I-plate system. Volatiles increased plant growth significantly compared to control. Exposure of plant with bacteria volatiles reduced disease index from 80% to 40%. Pathogenic bacteria population in plant leaves reached up to 1.1×106 CFU/g aerial part wet weight, in volatile treatment, however pathogen population reached up to 1.3×108 in control plants. Expressions of PR-1, PDF1.2, and ChiB have been evaluated as marker genes for salicylic acid, jasmonic acid and ethylene-depended pathways, respectively. Bacteria volatiles boosted the expression of PR-1 and PDF1.2, significantly. These genes expressed strongly and rapidly which represent plant defense priming by bacteria volatiles. In conclusion, volatiles from B. subtilis GB03 not only improved plant growth significantly but also increased expression of defense-related genes and eventually suppressed disease in Arabidopsis.