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). May play an essential role in auxin-mediated organogenesis and in root gravitropic responses. Protein modification; protein ubiquitination. Expressed in the hypocotyl cells that would differentiate into vascular bundles. Highly expressed in primary root tips. The BTB/POZ domain mediates the interaction with some component of ubiquitin ligase complexes. Belongs to the NPH3 family.