• abscissic acid (ABA);
  • Arabidopsis thaliana;
  • biological control;
  • defense signalling;
  • hrp genes;
  • microarray;
  • Ralstonia solanacearum


  • Means to control bacterial wilt caused by the phytopathogenic root bacteria Ralstonia solanacearum are limited. Mutants in a large cluster of genes (hrp) involved in the pathogenicity of R. solanacearum were successfully used in a previous study as endophytic biocontrol agents in challenge inoculation experiments on tomato. However, the molecular mechanisms controlling this resistance remained unknown.
  • We developed a protection assay using Arabidopsis thaliana as a model plant and analyzed the events underlying the biological control by genetic, transcriptomic and molecular approaches.
  • High protection rates associated with a significant decrease in the multiplication of R. solanacearum were observed in plants pre-inoculated with a ΔhrpB mutant strain. Neither salicylic acid, nor jasmonic acid/ethylene played a role in the establishment of this resistance. Microarray analysis showed that 26% of the up-regulated genes in protected plants are involved in the biosynthesis and signalling of abscissic acid (ABA). In addition 21% of these genes are constitutively expressed in the irregular xylem cellulose synthase mutants (irx), which present a high level of resistance to R. solanacearum.
  • We propose that inoculation with the ΔhrpB mutant strain generates a hostile environment for subsequent plant colonization by a virulent strain of R. solanacearum.