Functional specialization of stomatal bHLHs through modification of DNA-binding and phosphoregulation potential

Developmental complexity often parallels expansion of transcription factor families, and highly similar proteins can play related but distinct roles in the development of cell lineages and cell types. Comparative sequence analyses can point to regions of proteins that may be involved in specialization, but complementary functional approaches are required to confirm these roles. Using the “natural laboratory” of stomatal development in which closely related basic helix–loop–helix (bHLH) transcription factors regulate distinct sequential processes, we assign functions to unique domains and identify functional divergences hidden within regions of sequence identity.