bHLH proteins know when to make a stoma

In Arabidopsis thaliana, stomata develop through a stereotypical pattern of cell divisions. Three recent publications demonstrate that three bHLH proteins act successively in such lineages to drive the formation of stomata. SPEECHLES drives the division that initiates the stomatal-cell lineage. Then MUTE induces the formation of the immediate stomatal precursor cell. Finally, FAMA causes the stomatal precursor cell to divide into the two guard cells that surround each stomatal pore.