Regulates microtubule function in seed development. Required for development of both embryo and endosperm tissue. Not essential for cell viability. Probably involved in the binding of beta-tubulin in the multimeric supercomplex. 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). Embryo lethality. Embryo development limited to the formation of a few giant cells lacking microtubules but not actin filaments, each with one to several nuclei. Failure to localize KNOLLE in mitotic cells. Presence of abnormal endosperm with giant polyploid nuclei. 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 TBCD family.