Utilization of mutants to analyze the interaction between Arabidopsis thaliana and its naturally root-associated Pseudomonas

A model system based on the Arabidopsis thaliana (L.) Heynh. Ws ecotype and its naturally colonizing Pseudomonas thivervalensis rhizobacteria was defi ned. Pseudomonas strains colonizing A. thaliana were found to modify the ro ot architecture either in vivo or in vitro. A gnotobiotic system using bact eria labelled with green fluorescent protein revealed that P. thivervalensi s exhibited a colonization profile similar to that of other rhizobacterial species, Mutants of A. thaliana affected in root hair development and possi ble hormone perception were used to analyze the plant genetic determinants of bacterial colonization. A screen for mutants insensitive to P. thiverval ensis colonization yielded two mutants found to be auxin resistant. This fu rther supports a proposed role for bacterial auxin in inducing morphologica l modifications of roots. This work paves the way for studying the interact ion between plants and non-pathogenic rhizobacteria in a gnotobiotic system , derived from a natural association, where interactions between both partn ers can be genetically dissected.