Bacterial cell wall homeostasis is an intricately coordinated process that ensures that envelope integrity is maintained during cell growth and division, but can also adequately respond to growth-limiting conditions such as phosphate starvation. In Bacillus subtilis, biosynthesis of the two major cell wall components, peptidoglycan and anionic polymers, is controlled by a pair of paralogous two-component systems, WalRK and PhoPR respectively. Favorable growth conditions allow for a fast rate of cell wall biosynthesis (WalRK-ON) and the incorporation of the phosphate-containing anionic polymer teichoic acids (PhoPR-OFF). In contrast, growth-restricted cells under phosphate-limiting conditions reduce the incorporation of peptidoglycan building blocks (WalRK-OFF) and switch from the phosphate-containing teichoic acids to the phosphate-free anionic polymer teichuronic acid (PhoPR-ON). Botella etal. (2014) deepen our knowledge on the PhoPR system by identifying one signal that is perceived by its histidine kinase PhoR. In fast-growing cells, intracellular intermediates of teichoic acid biosynthesis are sensed by the cytoplasmic Per-Arnt-Sim domain as an indicator of favorable conditions, thereby inhibiting the autokinase activity of PhoR and keeping the system inactive. Depletion of teichoic acid building blocks under phosphate-limiting conditions relieves this inhibition, activates PhoPR-dependent signal transduction and hence the switch to teichuronic acid biosynthesis.