Sample collection and extraction
Shoots were harvested at 11 dpi for Arabidopsis (N=10) and Broccoli (N=5) seedlings, and at 14 dpi for Artemisia (N=8). For each plant species x rhizobacteria combination, four biological replicates comprising the aforementioned number of plants were used. Briefly, shoots were snap frozen in liquid nitrogen and ground to a fine powder under continuous cooling and kept at -80 °C until further use. For extraction of semipolar metabolites, 300 µL of 99.89% methanol containing 0.13% (v/v) formic acid was added to 100 mg powdered plant material in 2 mL round-bottom Eppendorf tubes, and sonicated for 15 min followed by centrifugation for 15 min at 20,000 Xg . The supernatants were transferred to a 96-well plate (AcroPrepTM, 350 µL, 0.45µm, PALL) and vacuum filtrated into a 96-deep-well autosampler plate (Waters) using a Genesis Workstation (Tecan Systems).