Activator protein that regulates the ubiquitin ligase activity and substrate specificity of the anaphase promoting complex/cyclosome (APC/C). Necessary and sufficient for endoreduplication and correct cell expansion. Controls meristem size by stimulating endoreduplication in the elongation zone. Protein modification; protein ubiquitination. Associates with the APC/C complex. Interacts with CDC20-1, CDC20-2, CYCA1-1, CYCA1-2, CYCA3-4, CYCB1-1 AND CYCB1-2. Binds to GIG1 and PYM. Expressed in seedlings, flowers, leaves and roots. Expressed in the differentiating cell files of the root elongation zone. Expressed from late M until late S-early G2 phases. Reduced endoreduplication and reduced expansion in trichomes and other leaf cells. Longer roots. Root meristem contains more dividing cells with a delayed onset of endoreduplication. FZR2 controls the induction of early rounds of endoreduplication while the remaining rounds may be mediated by FZR1 and FZR3. FZR1 and FZR2 are functional homologs, and their functional divergence in root development arises from the different expression patterns. Belongs to the WD repeat CDC20/Fizzy family.