Transcription factor. Together with FMA and SPCH, regulates the stomata formation. Required for the differentiation of stomatal guard cells, by promoting successive asymmetric cell divisions and the formation of guard mother cells. Promotes the conversion of the leaf epidermis into stomata. Homodimer. Leaf epidermis and flowers. Strongly expressed in meristemoids and at lower levels in guard mother cells (GMCs) and guard cells. By UV, flagellin, and jasmonic acid (JA) treatments. Extended C-terminus.