title: MICROTUBULE ORGANIZATION 1 regulates structure and function of microtubule arrays during mitosis and cytokinesis in the Arabidopsis root.
abstract: MICROTUBULE ORGANIZATION 1 (MOR1) is a plant member of the highly conserved MAP215/Dis1 family of microtubule-associated proteins. Prior studies with the temperature-sensitive mor1 mutants of Arabidopsis (Arabidopsis thaliana), which harbor single amino acid substitutions in an N-terminal HEAT repeat, proved that MOR1 regulates cortical microtubule organization and function. Here we demonstrate by use of live cell imaging and immunolabeling that the mor1-1 mutation generates specific defects in the microtubule arrays of dividing vegetative cells. Unlike the universal cortical microtubule disorganization in elongating mor1-1 cells, disruption of mitotic and cytokinetic microtubule arrays was not detected in all dividing cells. Nevertheless, quantitative analysis identified distinct defects in preprophase bands (PPBs), spindles, and phragmoplasts. In nearly one-half of dividing cells at the restrictive temperature of 30 degrees C, PPBs were not detected prior to spindle formation, and those that did form were often disrupted. mor1-1 spindles and phragmoplasts were short and abnormally organized and persisted for longer times than in wild-type cells. The reduced length of these arrays predicts that the component microtubule lengths are also reduced, suggesting that microtubule length is a critical determinant of spindle and phragmoplast structure, orientation, and function. Microtubule organizational defects led to aberrant chromosomal arrangements, misaligned or incomplete cell plates, and multinucleate cells. Antiserum raised against an N-terminal MOR1 sequence labeled the full length of microtubules in interphase arrays, PPBs, spindles, and phragmoplasts. Continued immunolabeling of the disorganized and short microtubules of mor1-1 at the restrictive temperature demonstrated that the mutant mor1-1(L174F) protein loses function without dissociating from microtubules, providing important insight into the mechanism by which MOR1 may regulate microtubule length.
authors.affiliation: Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
authors.forename: Eiko
authors.initials: E
authors.lastname: Kawamura
authors.forename: Regina
authors.initials: R
authors.lastname: Himmelspach
authors.forename: Madeleine C
authors.initials: MC
authors.lastname: Rashbrooke
authors.forename: Angela T
authors.initials: AT
authors.lastname: Whittington
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Gale
authors.forename: David A
authors.initials: DA
authors.lastname: Collings
authors.forename: Geoffrey O
authors.initials: GO
authors.lastname: Wasteneys
mesh_terms: D017360:Arabidopsis / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000502:physiology*; D002473:Cell Wall / Q000378:metabolism; D048749:Cytokinesis; D008856:Microscopy, Fluorescence; D008869:Microtubule-Associated Proteins / Q000502:physiology*; D022101:Microtubule-Organizing Center / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D008938:Mitosis; D005810:Multigene Family; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D008941:Spindle Apparatus / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D029681:Arabidopsis Proteins; C429183:MOR1 protein, Arabidopsis; D008869:Microtubule-Associated Proteins