Abstract
Microtubules orchestrate cell division and morphogenesis, but how they disassemble and reappear at different subcellular locations is unknown. Microtubule organizing centres are thought to have an important role, but in higher plants microtubules assemble in ordered configurations even though microtubule organizing centres are inconspicuous or absent. Plant cells generate highly organized microtubule arrays that coordinate mitosis, cytokinesis and expansion. Inhibiting microtubule assembly prevents chromosome separation1, blocks cell division2 and impairs growth polarity3. Microtubules are essential for the formation of cell walls, through an array of plasma-membrane-associated cortical microtubules whose control mechanisms are unknown. Using a genetic strategy to identify microtubule organizing factors in Arabidopsis thaliana, we isolated temperature-sensitive mutant alleles of the MICROTUBULE ORGANIZATION 1 (MOR1) gene. Here we show that MOR1 is the plant version of an ancient family of microtubule-associated proteins4. Point mutations that substitute single amino-acid residues in an amino-terminal HEAT repeat impart reversible temperature-dependent cortical microtubule disruption, showing that MOR1 is essential for cortical microtubule organization.
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Acknowledgements
R. E. Williamson provided support from the inception of this project and supplied EMS-mutagenized seed stock. The Arabidopsis Biological Resource Centre, Ohio State University, supplied BACs. We thank T. Hashimoto and K. Ueda for the GFP::TUA6 line, M. Luo and A. Chaudhury for the binary clone used in complementation, H. Kazama for helpful advice, R. Heady and A. Knox for microscopy assistance, and J. B. Gibson, B. E. S. Gunning and A. R. Hardham for comments on the manuscript. An Australian Research Council QEII Fellowship to G.O.W. supported this work. Coauthor contributions include: mutant identification and genetic analysis (G.O.W. and N.G.H.), gene mapping (O.V., K.-J.W., A.T.W. & G.O.W.), cloning and sequence analysis (A.T.W., K.-J.W., M.C.R. & G.O.W.), microtubule dynamics (G.O.W.) and morphological analysis (K.S., N.G.H. & G.O.W.).
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Supplementary gene maps
AtMOR1 nucleotide and deduced amino acid sequences. Splice junctions (><) are shown and exons are numbered from the start codon (underlined). mor1 mutation sites are indicated (Ñ). This RT-PCR-derived sequence data (GenBank AF367246) is slightly different to that predicted (GenBank AC006068.3) due to inaccurate prediction of some splice sites by the latter.
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Whittington, A., Vugrek, O., Wei, K. et al. MOR1 is essential for organizing cortical microtubules in plants. Nature 411, 610–613 (2001). https://doi.org/10.1038/35079128
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DOI: https://doi.org/10.1038/35079128
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