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

BACKGROUND: 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. SCOPE: 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.