Negative regulator of the anaphase-promoting complex/cyclosome (APC/C) ubiquitin ligase required for proper mitotic and meiotic progression and cell fate determination. Involved in entry into both meiosis I and meiosis II. Prevents endomitosis by preferentially inhibiting APC/C(CDC20). Required for megagametophyte and endosperm development. Triggers mitotic cyclins (e.g. CYCB1-1 and CYCB1-2) accumulation. Confers immunity to bacterial pathogens (e.g. Pseudomonas syringae pv. tomato DC3000), which is associated with increased expression of disease resistance (R) genes. GIG1 and PANS1 are part of a network linking centromere cohesion and cell cycle progression through control of APC/C activity. Interacts with APC/C activators such as FZR1, FZR2, FZR3, CDC20.1 and CDC20.5. Expressed in rapidly dividing tissues such as shoot apical meristem and young leaves. Associated with cell division but also with specific cell types. Levels fade progressively in a basipetal fashion as the leaf develops. In the epidermis of cotyledons and leaves, observed in dividing and recently divided stomatal precursor cells, especially in dividing guard mother cells and young guard cells. Also present in asymmetrically dividing meristemoid mother cells and meristemoids. In roots, expressed preferentially in the division zones of root tips. Phosphorylated by CDKA-1 in complex with CYCA1-2. Ectopic endomitosis during somatic cell division leading to gigas cells, large guard cells, and round cells containing large polyploid nuclei in cotyledons. Enhancer of the myb3r4 mutant phenotype. Enhancer of bon1-2 phenotype, leading to dwarf and bushy phenotype with many lateral shoots. Production of diploid gametes by skipping the second meiotic division; male meiosis leads to dyads instead of tetrads, and selfed progeny provides tetraploids (4n) and triploids (3n), but no diploid (2n) plants.