A key issue in developmental biology is how particular processes are coordinated in time: for example, what determines when development of a particular organ starts and how quickly it proceeds? Jennifer Nemhauser and colleagues explore this problem in Arabidopsis, using auxin-mediated regulation of lateral root development as a model (p. 905). Specifically, they investigate the consequence of manipulating the degradation rate of the auxin-responsive transcriptional co-repressor IAA14, the mutation of which is known to affect lateral root formation. Using a synthetic biology approach, the authors generate several versions of IAA14 that show varying degradation kinetics upon auxin stimulation, and then generate transgenic plants expressing each version from the wild-type promoter. They find that both the density and timing of lateral root emergence inversely correlates with IAA14 stability: more stable variants show fewer lateral roots and these roots take longer to initiate. IAA14 is part of a large family of Aux/IAA repressors and these data suggest that regulating the degradation rate of these proteins could act as a tunable timer for developmental progression in plants.