Transcription factor that plays a role in floral organogenesis. Promotes the growth of carpel margins and of pollen tract tissues derived from them. Homodimer (Probable). Interacts with HEC1, HEC2 AND HEC3. Binds to RGL2 and RGA. Expressed in lateral root caps, young leaves, stipules, maturing pith cells of the stem, differentiating vascular cells, shoot apical meristems and flowers. During flower initiation, expressed in the peripheral zone of the shoot apical meristem. Confined to the anlagen of successive flower buds yet to arise. Later expressed in abaxial and adaxial sepal primordia, but not in sepals. When sepals initiate, localized in the region interior to them. Within the gynoecium, detected in the initiating and developing medial regions, and then in the developing septum and stigma. SPT expression also occurs in sub-regions of developing ovules, and in the wall and dehiscence zone of the maturing fruit. As the petals develop, becomes restricted to the adaxial epidermis. In stamen expression increase in the vicinity of the archesporial cells and in cells undergoing divisions to produce sporogenous and secondary parietal cells of the anther locules. Expressed in the tapetum and microspore mother cells until the initiation of meiosis. Also detected in stomium and filaments. Down-regulated by the A class gene AP2 in the first whorl and by ARF3/ETT in gynoecium.