Priming of Induced Plant Defense Responses

Upon infection by a pathogen, colonization of the roots by certain beneficial microbes, or after treatment with various chemicals, plants can establish a unique physiological situation which is called the "primed" state of the plant. In the primed condition, plants respond faster and/or more strongly with the activation of defense responses when subsequently challenged by microbial pathogens, herbivorous insects, or abiotic stresses. The potentiated activation of defense responses in primed plants is frequently associated with enhanced resistance to the challenging stress. Although priming has been known as a component of various induced resistance phenomena for decades, most of the progress in the understanding of the phenomenon has been made over the past decade. Here, I summarize the current knowledge of priming, its role in various forms of induced resistance, and its relevance for plant protection in the greenhouse and in the field.