Bacterial auxin signaling: comparative study of growth induction in Arabidopsis thaliana and Triticum aestivum

Auxin-producing rhizobacteria were evaluated for the role of their auxin signaling in enhancing the growth of Arabidopsis thaliana (L.) Heynh. and Triticum aestivum L. Arabidopsis thaliana wild type Columbia (Col-0) in comparison with phytohormone mutant lines aux1-7 (insensitive to auxin and ethylene), axr4-1 (insensitive to auxin), and eir1-1 (insensitive to ethylene) was used as a model system. Bacterization of wild type Col-0 recorded significant increases in shoot length (38%) and number of siliqua (180%) with Bacillus subtilis TpP-1 over the controls. Inoculation with aux1-7 and axr4-1 showed statistically comparable results for growth parameters as compared to their respective controls. Treatment of eir1-1 with Pseudomonas sp. AvH-4 and Bacillus subtilis TpP-1 recorded significant increases in shoot length (9%) and number of siliqua (20%), respectively. The pattern of growth response of aux1-7, axr4-1, and eir1-1 indicated that bacterial auxin and ethylene signaling is involved in the growth promotion of A. thaliana. For T. aestivum, significant increases in number of tillers (74%) and seed weight (26%) were recorded with Pseudomonas sp. AvH-4. Results of this study suggested that growth induction by B. subtilis TpP-1, Pseudomonas sp. AvH-4, and Pseudomonas aeruginosa As-17 in A. thaliana is associated with bacterial auxin signaling.