May act as a substrate-specific adapter of an E3 ubiquitin-protein ligase complex (CUL3-RBX1-BTB) which mediates the ubiquitination and subsequent proteasomal degradation of target proteins (By similarity). Coregulates with PID the auxin-mediated plant organogenesis. Regulates cotyledon development through control of PIN1 polarity. May play an essential role in root gravitropic responses. Protein modification; protein ubiquitination. Colocalized with PID. Expressed mainly in the apical regions of embryos including cotyledon tips and the apical meristem. Highly expressed in primary root tips. Detected in globular-stage embryos in the epidermis with the highest concentration at the apical region. At early heart stage, expression is restricted to the two cotyledon primordia and the meristem. In the late heart to torpedo stages, expression is restricted to the meristem and the cotyledon tips. In mature embryos, stricly expressed at the apical meristem. During seedling development, highly expressed in young leaf primordia and the apical meristems. Detected in the protodermal cell layer of the embryo and the meristem L1 layer at the site of organ initiation. After transition to the reproductive phase, detected in the inflorescence meristem and at various stages of floral development. The BTB/POZ domain mediates the interaction with some component of ubiquitin ligase complexes. Seedlings with abnormal cotyledons. Belongs to the NPH3 family.