Signalling in Rhizobacteria‐Induced Systemic Resistance in Arabidopsis thaliana

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Abstract
To protect themselves from disease, plants have evolved sophisticated defence mechanisms in which the signal molecules salicylic acid, jasmonic acid and ethylene often play crucial roles. Elucidation of signalling pathways controlling disease resistance is a major objective in research on plant‐pathogen interactions. The capacity of a plant to develop a broad spectrum, systemic acquired resistance (SAR) after primary infection with a necrotizing pathogen is well‐known and its signal transduction pathway extensively studied. Plants of which the roots have been colonized by specific strains of non‐pathogenic fluorescent Pseudomonas spp. develop a phenotypically similar form of protection that is called rhizobacteria‐mediated induced systemic resistance (ISR). In contrast to pathogen‐induced SAR, which is regulated by salicylic acid, rhizobacteria‐mediated ISR is controlled by a signalling pathway in which jasmonic acid and ethylene play key roles. In the past eight years, the model plant species Arabidopsis thaliana was explored to study the molecular basis of rhizobacteria‐mediated ISR. Here we review current knowledge of the signal transduction steps involved in the ISR pathway that leads from recognition of the rhizobacteria in the roots to systemic expression of broad‐spectrum disease resistance in aboveground foliar tissues.