Transcription factor acting as an integration node for stomata and brassinosteroid (BR) signaling pathways to control stomatal initiation and development (PubMed:22466366, PubMed:28507175). Activates transcription when in the presence of SCRM/ICE1 (PubMed:28507175). Functions as a dimer with SCRM or SCRM2 during stomatal initiation (PubMed:18641265). Required for the initiation, the spacing and the formation of stomata, by promoting the first asymmetric cell divisions (PubMed:25843888, PubMed:25680231, PubMed:19008449). Together with FMA and MUTE, modulates the stomata formation. Involved in the regulation of growth reduction under osmotic stress (e.g. mannitol), associated with a quick decrease of meristemoid mother cells (MMCs) number lower stomatal index and density (PubMed:25381317). Negatively regulated through phosphorylation by the MAPK module (PubMed:19008449). Activity is constrained by polarized BASL in stomatal lineage ground cells (SLGCs) undergoing ACD (PubMed:27746029). Homodimer (Probable). Forms dimers with SCRM and SCRM2 (PubMed:18641265, PubMed:28507175). May interact with CDKA-1 (PubMed:25680231). Expressed in developing leaf epidermis (PubMed:17183265). Reduced accumulation in the stomatal lineage ground cells (SLGCs) where BASL is polarized in the cell cortex (PubMed:27746029). Observed in small cells of non-protruding hypocotyl cell files and of developing cotyledon epidermis (PubMed:22466366). Restricted to meristemoids (stomatal precursor cell) in leaves epidermis, mostly in dividing cells of non-protruding cell files (PubMed:25680231, PubMed:18641265, PubMed:19008449). First observed in a subset of undifferentiated epidermal cells, often by pair of neighboring cells. Later confined to small epidermal cells, including cells that have recently divided next to stomatal lineage cells. Also expressed in stomatal lineage cells, fading out progressively during meristemoid determination. Repressed by brassinazole (BRZ), thus leading to a reduced number of stomata in hypocotyls (PubMed:25680231). Inhibited by low relative humidity (LRH) via epigenetic CG methylation, thus leading to a reduced stomatal index (PubMed:22442411). Repressed by YDA (at protein level) (PubMed:19008449). Post-transcriptional decrease of protein level in response to osmotic stress (e.g. mannitol), through the action of a mitogen-activated protein kinase (MAPK) cascade; this repression is reversed by the MAPK kinase inhibitor PD98059 (PubMed:25381317). Phosphorylated by ASK7/BIN2 and ASK3/SK12; this post-translational modification inhibits activity and limit epidermal cell proliferation (PubMed:30429609, PubMed:22466366). Phosphorylation by MPK3 and MPK6 leads to the inhibition of stomatal fate and to degradation (PubMed:25843888, PubMed:19008449). Stabilized by CDKA-1-mediated phosphorylation at Ser-186 which promotes stomatal development (PubMed:25680231). Stomatal defects in cotyledons and hypocotyls.