Bacterial strains and growth conditions
Escherichia coli DH5α strains were grown at 37°C in Luria Bertani medium [LB medium: 30 g/L bacto-trypone, 15 g/L yeast extract and 30 g/L sodium chloride (NaCl) at pH 7.5] and supplemented with specific antibiotics: ampicillin 50 μg/ml, kanamycin 50 μg/ml. A. rhizogenes Arqua1 strains were grown at 28 °C in TY medium [5 g/L bacto-trypone, 3 g/L yeast extract and 6 mM of calcium chloride (CaCl2)] supplemented with spectinomycin and streptomycin (100 μg/ml). S. meliloti RCR2011 were grown at 30°C in LB medium complemented with 2.5 mM CaCl2, 2.5 mM magnesium sulphate (MgSO4).