Early Arabidopsis Root Hair Growth Stimulation by Pathogenic Strains of Pseudomonas Syringae

The study demonstrated that pathogenic strains of Pseudomonas syringae (Psm and Pst) stimulated early root hair growth and inhibited primary root growth in Arabidopsis thaliana, similar to plant growth-promoting rhizobacteria. This response occurred within hours of bacterial contact and required functional ethylene signaling and an efficient exocyst-dependent secretory machinery. Mutants with impaired ethylene perception (ein2) and defects in the exocyst complex (exo70A1) showed compromised root hair growth stimulation. The response was not directly linked to changes in auxin levels but could be modulated by FLS2 signaling, as pretreatment with Flg22 peptide prior to Psm inoculation abolished the root hair growth stimulation.