AbstractSoil bacteria promote plant growth and protect against environmental stresses, but the mechanisms involved remain poorly characterized, particularly when there is no direct contact between the roots and bacteria. Here, we explored the effects ofPseudomonas oryzihabitansPGP01 on the root system architecture (RSA) inArabidopsis thalianaseedlings. Significant increases in lateral root (LR) density were observed when seedlings were grown in the presence ofP. oryzihabitans, as well as an increased abundance of transcripts associated with altered nutrient transport and phytohormone responses. However, no bacterial transcripts were detected on the root samples by RNAseq analysis, demonstrating that the bacteria do not colonize the roots. Separating the agar containing bacteria from the seedlings prevented the bacteria-induced changes in RSA. Bacteria-induced changes in RSA were absent from mutants defective in ethylene response factor (ERF109), glutathione synthesis (pad2-1,cad2-1, andrax1-1) and in strigolactone synthesis (max3-9andmax4-1) or signalling (max2-3). However, theP. oryzihabitans-induced changes in RSA were similar in the low ascorbate mutants (vtc2-1andvtc2-2) to the wild-type controls. Taken together, these results demonstrate the importance of non-volatile signals and redox mechanisms in the root architecture regulation that occurs following long-distance perception ofP. oryzihabitans.