Signaling during rhizobacteria-induced systemic resistance in Arabidopsis

Abstract

Arabidopsis plants of which the roots are colonized by specific strains of non-pathogenic fluorescent Pseudomonas bacteria develop an induced systemic resistance (ISR) that, unlike pathogen- induced systemic acquired resistance (SAR), is independent of salicylic acid (SA) but requires sensitivity to jasmonic acid (JA) and ethylene (ET). Various Pseudomonas spp. strains induce broad-spectrum disease resistance in plants in a bacterial strain/plant species-specific manner. Different bacterial determinants appear to be involved in triggering ISR, e.g. lipopolysaccharides (LPS), siderophores, flagella and antibiotics. Combining ISR and SAR increased resistance against pathogens that are resisted by both JA/ET- and SA-dependent defenses, but not against pathogens that are affected exclusively by either ISR or SAR. Unlike SAR, the onset of ISR is not associated with major changes in gene expression, but upon challenge inoculation ISR-expressing plants are primed to express certain sets of genes more quickly and/or at higher levels.