Abstract: Upon infection by a pathogen or upon treatment with certain commercial fungicidesplants can develop resistance to a broad spectrum of pathogens and/or abiotic stress. The inducedresistance is frequently associated with the so-called “priming” of cells. Priming is thephenomenon that enables cells to respond to much lower levels of a stimulus in a more rapid androbust manner than non-primed cells (Prime-A-Plant Group, 2006). It has been hypothesized thatpriming involves accumulation of dormant signaling components that are not used until challengeexposure to pathogens or abiotic stress. However, until recently the identity of such signalingcomponents has remained elusive. We showed that during development of induced resistance inArabidopsis thaliana, priming is associated with accumulation of mRNA and inactive protein ofmitogen-activated protein kinases (MPK) 3 and MPK6. Upon challenge exposure of the plants toPseudomonas syringae pv. maculicola or infiltration of water into leaves, these two enzymeswere more strongly activated in primed plants than in non-primed plants. This elevated activationwas linked to enhanced defense gene expression and development of induced resistance. Inaddition, priming of defense gene expression and induced resistance were lost or reduced in mpk3or mpk6 mutants (Beckers et al., 2009). Our findings argue that pre-stress deposition of thesignaling components MPK3 and MPK6 is a critical step in priming plants for full induction ofdefense responses during induced resistance. The role of MPK3 and MPK6 in induced resistanceand the potential of priming for modern pest management in the field is illustrated.