Has a role in the cofactor-dependent pathway of microtubule biogenesis. Not essential for cell viability. May play a regulatory role in sequestring TFCD. Supercomplex made of cofactors A to E. Cofactors A and D function by capturing and stabilizing tubulin in a quasi-native conformation. Cofactor E binds to the cofactor D-tubulin complex; interaction with cofactor C then causes the release of tubulin polypeptides that are committed to the native state (By similarity). Expressed in seedlings, leaves, roots and inflorescences. Embryo lethality. Embryo development limited to the formation of a few giant cells lacking microtubules but not actin filaments. Failure to localize KNOLLE in mitotic cells. Giant nuclei and nucleoli found in both the embryo and endosperm tissue. Belongs to the PILZ group of genes that disrupt, when mutated, the microtubule cytoskeleton and produce mushroom-shaped ('pilz' in German) embryos. Belongs to the small GTPase superfamily. Arf family.