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First published online December 23, 2005; 10.1104/pp.105.069989 Plant Physiology 140:102-114 (2006) © 2006 American Society of Plant Biologists MICROTUBULE ORGANIZATION 1 Regulates Structure and Function of Microtubule Arrays during Mitosis and Cytokinesis in the Arabidopsis Root1,[W]Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 (E.K., G.O.W.); Plant Cell Biology Group, Research School of Biological Sciences, Australian National University, Canberra, Australian Capital Territory 2601, Australia (E.K., R.H., M.C.R., A.T.W., D.A.C., G.O.W.); and Commonwealth Scientific and Industrial Research Organization, Plant Industry, Canberra, Australian Capital Territory 2601, Australia (K.R.G.)
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°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 mor1-1L174F protein loses function without dissociating from microtubules, providing important insight into the mechanism by which MOR1 may regulate microtubule length.
1 This work was supported by the Australian Research Council (DP0208872), the Natural Sciences and Engineering Research Council of Canada (298264–04), and Bayer CropScience. E.K. received an Australian National University Ph.D. Scholarship and a University of British Columbia Graduate Fellowship. 2 Present address: Office of the Gene Technology Regulator, Pharmacy Guild House, 15 National Circuit, Barton, ACT 2600, Australia. 3 Present address: Policy Coordination and Environment Protection Division, Department of the Environment and Heritage, GPO Box 787, Canberra, ACT 2601, Australia. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Geoffrey O. Wasteneys (geoffwas{at}interchange.ubc.ca). [W] The online version of this article contains Web-only data. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.069989. * Corresponding author; e-mail geoffwas{at}interchange.ubc.ca; fax 604–822–6089. Received August 17, 2005; returned for revision November 18, 2005; accepted November 22, 2005. This article has been cited by other articles:
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