Transcription activator that binds DNA on 5'-ACTCTAC-3' and promotes auxin homeostasis-regulating gene expression (e.g. YUC genes), as well as genes affecting stamen development, cell expansion and timing of flowering. Synergistically with other SHI-related proteins, regulates gynoecium, stamen and leaf development in a dose-dependent manner, controlling apical-basal patterning. Promotes style and stigma formation, and influences vascular development during gynoecium development. May also have a role in the formation and/or maintenance of the shoot apical meristem (SAM). Suppressor of the gibberellin (GA) signal transduction. Forms a heterodimer with LRP1. Expressed in young organs such as shoot apices and root tips. Present in roots, stems, flowers, leaves, hydathodes and siliques. In germinating seeds, first detected at about 48 h after imbibition. In young seedlings grown in continuous light, present in the root/shoot transition zone, in the apex, and in the apical region of the cotyledons. Later observed in lateral root primordia and in emerging lateral roots, particularly in the root tips, as well as in the shoot apex and in the new leaves, especially in the apical and lateral hydathodes. In adult plants, accumulates in lateral root tips, lateral root primordia, and axillary shoot primordia. In flowers, expressed in the style and stigmatic surface of the pistil and in the receptacle (base) of the flower throughout the development of the pistil until anthesis and later in the silique. Fades out after fertilization. High gibberellin (GA) levels associated with dwarfism, short hypocotyl, narrow leaves, reduced apical dominance, and late flowering, but more flowers. Belongs to the SHI protein family.