Probable transcription factor required to initiate organ founder cells in a lateral domain of shoot meristems. Involved in the lateral sepal axis-dependent development of flowers, probably by regulating the proliferation of L1 cells at the lateral region of flower primordia. Required for the formation of the margin cells of the first and second whorl organs. Expressed in aerial parts of seedlings, inflorescences and flowers at low level. Expressed in a restricted number of L1 cells at the lateral regions of flower primordia. First expressed in the L1 cells of the lateral regions of a flower primordium at early stage 1, in which the lateral sepals are expected to develop at a later stage. It then rapidly decreases at the late stage 1 and disappears at stage 2. At stage 3, it reappears in all four-sepal young primordia. Not detected at the central zone of the inflorescence meristem and the floral meristem. In stages 4 through 6, when four sepals develop to enclose the flower bud, it is localized at the lateral edges of the four sepals and forms an arch of the L1 cells at the margin of sepals. Expressed in the young primordia of petals and stamens. As the petals and stamens develop, it is limited at the margins of petals and stamens in a way similar to that of sepals. In the vegetative phase, it is expressed at the lateral regions of young leaf primordia, as well as in flowers and floral organs. Belongs to the WUS homeobox family.