Should I fight or should I grow now? The role of cytokinins in plant growth and immunity and in the growth–defence trade-off

Perception and activation of plant immunity require a remarkable level of signalling plasticity and control. In Arabidopsis and other plant species, constitutive defence activation leads to resistance to a broad spectrum of biotrophic pathogens, but also frequently to stunted growth and reduced seed set. Plant hormones are important integrators of the physiological responses that influence the outcome of plant-pathogen interactions.We review the mechanisms by which the plant hormone cytokinin regulates both plant growth and response to pathogens, and how cytokinins may connect these two processes, ultimately affecting the growth trade-offs observed in plant immunity.