Microtubule-binding protein that is essential for cortical microtubules organization and function. Essential for maintaining the interphase cortical array and for correct morphogenesis. Promotes rapid growth and shrinkage of microtubules and suppresses the pausing of interphase microtubules. Regulates the structure and function of microtubule arrays during mitosis and cytokinesis. Probably not required for cellulose microfibrils alignment in roots. Associated with microtubules in interphase arrays, preprophase bands, spindles, and phragmoplasts. Expressed in roots, cotyledons, rosette leaves, stems, open flowers and green siliques. Homozygous lethal in gem1-1 mutant. No visible phenotype under normal growth condition in mor1-1 and mor1-2 mutants, but the restrictive temperature of 29 degrees Celsius causes cortical microtubule shortening and disorganization, left-handed helical growth of root, disrupts microtubule arrays during mitosis and cytokinesis and alters plant morphology and organ development. Aberrant cytokinesis and cell division pattern during pollen mitosis in heterozygous gem1-1 and gem1-2 mutants. Belongs to the TOG/XMAP215 family. Truncated N-terminus.