Involved in the abaxial cell fate determination during embryogenesis and organogenesis. Regulates the initiation of embryonic shoot apical meristem (SAM) development (PubMed:10457020, PubMed:12417699, PubMed:19837869). Contributes to the repression of KNOX genes (STM, KNAT1/BP and KNAT2) to avoid ectopic meristems. Binds DNA without sequence specificity (PubMed:10457020, PubMed:12417699). Interacts with SPL/NZZ (PubMed:15299139, PubMed:25527103). Interacts with SPEAR2 (PubMed:25527103). Binds to LUG and LUH; these complexes promote adaxial cell identity in leaves as well as embryonic shoot apical meristem (SAM) initiation and postembryonic SAM maintenance (PubMed:19837869). A number of isoforms are produced. According to EST sequences. Expressed in abaxial regions of lateral aerial organ primordia leading to cotyledons, leaves, flower meristems, sepals, petals, stamen and carpels, but not in roots. Expressed in subepidermal cells of anlagen regions, then in abaxial part of primordia and finally in differentiating organs. Levels decrease in differentiated organs. In embryo the expression starts during the heart stage in the cotyledon anlagen. Later, expression expands to abaxial domain of the cotyledon primordia and decrease as the embryo matures. In stamen, expression restricted to the abaxial region differentiating into the connective. In gynoecium, expressed in the abaxial cell layers differentiating into the valves. Leaves polarity and growth defects. Belongs to the YABBY family.