Exhibits E2-dependent E3 ligase activity (PubMed:22897245). Involved in pollen mitosis II (PMII) regulation during male gametogenesis (PubMed:22897245). S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts with At1g78040, At1g10650, VHA-c4/AVAP4, VHA-c''2/VMA16 and TUFA. Associated with intracellular membranes and in the tonoplast and endosomes in the germinating pollen tubes. Expressed in the shoot apical meristems (SAM), root tips, pollen and inflorescences. In young seedlings, expressed in the shoot apical meristem (SAM) and in root tips (PubMed:22897245). In inflorescence, specifically observed in mature pollen (PubMed:22897245). Present from the early bicellular pollen stage to the mature pollen stage; levels in vegetative cells increase during the development of pollen (PubMed:22897245). Detected in the germinating pollen tubes (PubMed:22897245). No obvious defects during the vegetative developmental stage (PubMed:22897245). The double mutant lacking both APD1 and APD2 exhibits an increased percentage of bicellular-like pollen at the mature pollen stage (PubMed:22897245). Plants lacking APD1, APD2, APD3 and APD4 are defective for cell division in male gametogenesis resulting in severe abnormal bicellular-like pollen phenotypes (PubMed:22897245).