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).