MOR1 and its function in microtubule organization, cell division and cell elongation

Abstract

MICROTUBULE ORGANIZATION 1 (MOR1) is a plant member of the TOGp-Dis1-XMAP215 class of microtubule-associated proteins. Single amino acid substitutions in an N-terminal HEAT repeat of this 217 kDa Arabidopsis protein generate short, misaligned cortical microtubules at 29*C. The N-terminal HEAT repeat is strongly conserved in all known eukaryotic homologues of MOR1.
The mor1-1 and mor1-2 mutations impair growth anisotropy and directional handedness in all organs. Within hours of microtubule disorganization, we detect left-handed twisting and, later, radial swelling. Although tip growth continues, root hairs develop an antler-like appearance, demonstrating that microtubules help to stabilize tip growth. The gemini1 pollen-defective mutants are allelic to MOR1 and a tobacco homologue has recently been isolated from phragmoplasts, demonstrating a role for MOR1 in the cytokinetic apparatus and cytoplasmic polarization. An amino-terminus-specific antibody labels microtubules in all arrays throughout the cell cycle, strongly supporting a ubiquitous association of MOR1 with all microtubule arrays.