Abstract
OBJECTIVE: Plant defence against pathogens typically requires salicylic acid (SA) biosynthesis or accumulation or the activation of the SA signalling pathway. However, SA overaccumulation is known to impair plant development, and previous work has shown that SA biosynthesis or signalling can interfere with the activities of plant-beneficial microbes but in a microbial species-dependent manner. This study investigated the effects of endogenous levels of SA in Arabidopsis on the growth-promoting activity of the beneficial rhizobacterium Pseudomonas simiae WCS417r (hereinafter Ps WCS417r). RESULTS: Wild-type levels of SA limited Ps WCS417r-mediated plant growth, as the SA-deficient Arabidopsis mutant sid2-2 accumulated more biomass in response to Ps WCS417r treatment than did the wild-type plants in response to Ps WCS417r treatment, and the SA-overaccumulator cpr5 yielded less biomass than did the wild-type plants. Analysis of previously generated and publicly available plant gene expression datasets revealed modest downregulation of EPS1, a key gene that contributes to SA accumulation, in the roots of Arabidopsis wild-type plants treated with Ps WCS417r. These results suggest that SA accumulation strongly limits the potential of some plant growth-promoting rhizobacteria, potentially minimizing their effectiveness in ensuring sustainable agriculture that is less reliant on chemical fertilizers.