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). Forms homodimers and heterodimers with LRP1. Expressed in flowers, seeds and seedlings. Expressed in the apical parts of the developing gynoecium. Detected throughout the youngest flower primordium. Later relocalizes towards the regions of the presumptive sepal anlagen and remains in sepal primordia until just after their emergence. Also observed on the abaxial side of the young floral meristem. Present in the newly arisen gynoecial primordium. Restricted to the apical parts of the carpels as the open-ended gynoecial cylinder elongates vertically. In the apical regions of the gynoecium, confined to a zone in the interphase between the style and the stigma and fades out later. Within the gynoecium, accumulates in ovule primordia, and, as the ovules developed, restricted to the epidermis of the developing funiculi, to the outer, but not the inner, integuments and to the tip of the nucellus. Also present in the cell layer of the septum that faces the ovary. In the embryo, detected in the cotyledon primordia during late globular to mid heart stage. In addition, transiently expressed in petal and stamen primordia and in the tapetum of the anthers. Regulated by ESR1 and ESR2. Gynoecia with aberrant style morphology. The double mutant sty1-1 and sty2-1 has a reduction in the amount of stylar and stigmatic tissues and decreased proliferation of stylar xylem, as well as shorter siliques and rosette and cauline leaves with a higher degree of serration. Hypersensitive to 1-N-naphthylphtalamic acid (NPA), but restored by exogenous application of auxin. Belongs to the SHI protein family.