Murashige skoog medium

The standard sunflower line RHA-274 was used as a control in this work, the seeds of which were germinated in wet perlite at 25°C and transferred to a germination chamber for 2 weeks for full seedling development. These seedlings were then moved to growth chambers at 25°C/15°C (day/night) equipped with fertirrigation lines, and they were maintained on a 16 h photoperiod at a photon flux density of 300 μmol m^-2 s^-1. Plant tissues at different stages of development (seeds, roots, stems, leaves, and cotyledons) were frozen and stored at -80°C until use.
Suspension-cultured tobacco (Nicotiana tabacum L. cv Bright Yellow-2) BY-2 cells (Kato et al., 1972 ) were grown in darkness at 26°C on a rotary shaker at 130 rpm in modified Murashige–Skoog medium (Sigma, St-Quentin Fallavier, France). BY-2 cells were maintained and then prepared for biolistic bombardment as described previously (Lingard et al., 2008 (link)), sub-culturing the cells every 7 days by transferring 1 mL into 50 mL of fresh medium.

Strains used in the study are listed in Table S1 in the supplemental material. B. subtilis strain NCIB 3610 was used as the wild-type strain, since its capacity to form biofilms is important for plant root colonization experiments longer than 4 h (Fig. 1B and 2B). OI WT and OI Δ10 strains, obtained from Georges Ordal (University of Illinois), are the only strains with a non-3610 background and were used only for the experiment shown in Fig. 4B. For routine growth, cells were propagated on Luria-Bertani (LB) medium. When necessary, antibiotics were used at the following concentrations: MLS (1 μg ml⁻¹ erythromycin, 25 μg ml⁻¹ lincomycin), spectinomycin (100 μg ml⁻¹), tetracycline (10 μg ml⁻¹), chloramphenicol (5 μg ml⁻¹), and kanamycin (10 μg ml⁻¹). Media used for these experiments were MSN (5 mM potassium phosphate buffer [pH 7], 0.1 M morpholinopropanesulfonic acid [pH 7], 2 mM MgCl₂, 0.05 mM MnCl₂, 1 μM ZnCl₂, 2 μM thiamine, 700 μM CaCl₂, 0.2% NH₄Cl) and MSNg (MSN supplemented with 0.05% glycerol, for root colonization).
The Col-0 A. thaliana ecotype was used throughout the study (a kind gift from Kamal Bouarab, Université de Sherbrooke). Seeds were surface sterilized with 70% ethanol followed by 0.3% (vol/vol) sodium hypochlorite and germinated on Murashige-Skoog medium (Sigma) with 0.7% agar with 0.05% glucose in a growth chamber at 25°C.