Mechanisms that control of root system architecture are well characterised but little is known about how these processes respond to plant growth promoting rhizobacteria. We therefore studied how the presence of Pseudomonas oryzihabitans PGP01 altered wild type RSA and how these changes were modified in mutants that are defective antioxidant capacity (vtc2-1, vtc2-2, pad2-1, cad2-1 and rax1-1) or strigolactone (SL) synthesis (max3-9 and max4-1) or signalling (max2-3). The presence of P. oryzihabitans PGP01 decreased the length of primary and lateral roots but increased the number of lateral roots and lateral root density in the wild type roots but not in the SL mutants. The presence of synthetic SL, GR24 in combination with P. oryzihabitans PGP01 significantly decreased the number and length of lateral roots in the WT, max3-9 and max4-1 but not max2-3 seedlings. Lateral root density was increased in all genotypes in the presence of bacterium, but this effect was less pronounced in the ascorbate deficient vtc2-1 and vtc2-2 roots and absent from glutathione –deficient (pad2-1, cad2-1 and rax1-1) seedlings. Taken together, these results demonstrate the importance of SL-mediated signalling in root responses to growth promoting rhizobacteria, as well roles of cellular redox controls in these processes.