Induced disease resistance signaling in plants

To protect themselves from disease, plants have evolved sophisticated inducible defense mechanisms in which the signal molecules salicylic
acid, jasmonic acid and ethylene often play crucial roles. Elucidation of signaling pathways controlling induced 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 signaling pathway in which the phytohormones jasmonic acid and ethylene play key
roles. In the past decade, the model plant species Arabidopsis thaliana has been extensively explored to study the molecular basis of
systemically induced resistance. Here we review the current knowledge on induced disease resistance signaling in plants.