Mob1 proteins are kinase regulators that are conserved among eukaryotes and which play a significant role in restraining tumor development. Pinosa et al. study the role of Mob1-like genes in development of Arabidopsis thaliana and find that the function of the gene appears to be indispensable for the growth of vegetative organs as well as for normal reproduction. In the primary root, reduced levels of Mob1A expression result in severe defects in tissue patterning of the stem cell niche and columella, and lead to a decrease in meristem size. Loss of Mob1A function results in a higher sensitivity of root growth to abscisic acid, and a specific plant function for the gene is suggested, namely the regulation of tissue growth in response to stress conditions.