sequences of bacteria
Leaves from 5-week-old greenhouse-grown soybean, maize, tomato, wheat plants were collected and pooled (3 leaves per replicate). Microbes were dislodged by two sequential washes in 20 mL sterile PBS (0.02 M, pH 7.0), vortexed for 10 min and sonicated at 40 kHz for 5 min. After centrifugation (12 000  g, 10 min, 4 C), pellets were resuspended in 1 mL PBS and filtered through a 301 m cell strainer to remove plant debris. Total microbial DNA was extracted using the SPINeasy Microbial DNA Kit (Qiagen) following the manufacturers protocol for plant-associated samples.