Plants, like all other organisms, need to assess and adapt to constant environmental changes throughout their life cycle. Defense responses to pathogens redirect cellular resources normally used in growth-related processes to the production of secondary metabolites, cell wall reinforcements and production of antimicrobial proteins. Immunity activation is therefore energetically costly, and requires complex mechanisms of regulation to allow for timely and appropriate levels of defense. Plant hormones are essential integrators of development and responses to the environment and as such are likely candidates for the regulation of physiological responses that influence the outcome of plant-pathogen interactions. I have uncovered an interplay between the plant hormones cytokinin and salicylic acid that regulates the immune responses of the model plant Arabidopsis thaliana and is mediated by a phosphorylation-dependent mechanism involving type-A response regulators and central defense signaling proteins. I will present how we are exploring this hormonal interplay to elucidate molecular mechanisms and key regulators controlling the growth-to-defense switch in plant immunity, using biochemical, genetic and systems biology approaches.