Immune signals shape root communities To thwart microbial pathogens aboveground, the plant Arabidopsis turns on defensive signaling using salicylic acid. In Arabidopsis plants with modified immune systems, Lebeis et al. show that bacterial communities change in response to salicylic acid signaling in the root zone as well (see the Perspective by Haney and Ausubel). Abundance of some root-colonizing bacterial families increased at the expense of others, partly as a function of whether salicylic acid was used as an immune signal or as a carbon source for microbial growth. Science , this issue p. 860 ; see also p. 788

Salicylic acid modulates colonization of the root microbiome by specific bacterial taxa