Microtubule-associated protein required for seed development and for microtubule function in the endosperm. Associates with nuclear microtubules during mitosis. Binds to microtubules of the spindle and spindle-poles and to midzone microtubules out of which the phragmoplast emerges. Not associated with cortical microtubules. Required for endosperm cellularization. May be bound and sequestered by GRF5 in an inactive soluble form during the early stages of mitosis. Interacts with GRF5 in a phosphorylation-independent manner. The binding to microtubules occurs independently of the interaction with GRF5. Microtubule-associated. Highly expressed in young siliques, seedlings, flower buds and open flowers. Weak expression in roots, and not detected in older siliques and mature leaves. Expressed in the embryo sac in prefertilization ovules and in seeds following fertilization. Detected in both embryo up to the heart stage and endosperm throughout most of the syncytial phase of endosperm development. Not detected in the cellularized endosperm, when cell division has ceased. Cell cycle-dependent regulation. Up-regulated during the G2/M phase. Phosphorylated. Aborted seed development. Belongs to the QWRF family.