Component of the cullin-RING ubiquitin ligases (CRL), or CUL3-RBX1-BTB protein E3 ligase complexes which mediate the ubiquitination and subsequent proteasomal degradation of target proteins. The functional specificity of the CRL complex depends on the BTB domain-containing protein as the susbstrate recognition component. Involved in embryo pattern formation and endosperm development. Required for the normal division and organization of the root stem cells and columella root cap cells. Regulates primary root growth by an unknown pathway, but in an ethylene-dependent manner. Functions in distal root patterning, by an ethylene-independent mechanism. Functionally redundant with CUL3B. Interacts with CSN2 and RBX1A. Interacts with BTB/POZ domain-containing proteins BPM1, BPM2, BPM3, BPM6, BT1, BT2, BT3, BT5, AT1G01640, AT1G21780 and AT5G48510 (PubMed:12615944, PubMed:15618422, PubMed:15659098, PubMed:15749712, PubMed:15772280). Interacts with SR1IP1 (PubMed:24528504). Expressed during flower development in floral meristem, sepals, petals, developing carpels, growing integuments and tetrads of megaspores. In mature ovules, expressed in the cells of the embryo sac. Expressed in the sporogenous cells, tetrads of microspores and mature pollen in stamens After fertilization, expressed in the embryo and endosperm at the globular and heart stages. The progressively decreases during ovule development and is not observed in the developing seed coat. Neddylated. Deneddylated via its interaction with the COP9 signalosome (CSN) complex. No visible phenotype under normal growth condition. Reduced sensitivity of the inhibition of hypocotyl growth in far-red light. Cul3a and cul3b double mutant is embryonic lethal (PubMed:16045478). Belongs to the cullin family.