Emerging parallels between stomatal and muscle cell lineages.

Stomatal development provides a model for understanding the molecular basis of how cell lineages are established and how cells differentiate into functionally mature structures. This article describes recent advancements in understanding the role of basic helixloop-helix (bHLH) proteins in stomatal lineage choice and differentiation in Arabidopsis. The emerging picture unravels that SPEECHLESS (SPCH), MUTE, and FAMA form heterodimers with SCREAM (SCRM)/ ICE1 and SCRM2 to specify the sequential steps during stomatal development. Intriguingly, both key genes and mechanisms needed for stomatal development are also required for the formation of skeletal muscle in animals.