First published online April 7, 2006; 10.1105/tpc.105.038364
The Plant Cell 18:1199-1212 (2006)
© 2006 American Society of Plant Biologists
-Tubulin Is Essential for Acentrosomal Microtubule Nucleation and Coordination of Late Mitotic Events in Arabidopsis[W]
Pavla Binarováa,1,2,
V ra Cenklováb,1,
Ji ina Procházkováa,c,1,
Anna Dosko ilováa,
Jind ich Volca,
Martin Vrlíka and
László Bögrec
a Institute of Microbiology, Academy of Sciences of the Czech Republic, 142 20 Prague 4, Czech Republic
b Institute of Experimental Botany, Academy of Sciences of the Czech Republic, 772 00 Olomouc, Czech Republic
c School of Biological Sciences, Royal Holloway, University of London, Egham TW20 OEX, United Kingdom
2 To whom correspondence should be addressed. E-mail binarova{at}biomed.cas.cz; fax 420-2-41062384.
-Tubulin is required for microtubule (MT) nucleation at MT organizing centers such as centrosomes or spindle pole bodies, but little is known about its noncentrosomal functions. We conditionally downregulated -tubulin by inducible expression of RNA interference (RNAi) constructs in Arabidopsis thaliana. Almost complete RNAi depletion of -tubulin led to the absence of MTs and was lethal at the cotyledon stage. After induction of RNAi expression, -tubulin was gradually depleted from both cytoplasmic and microsomal fractions. In RNAi plants with partial loss of -tubulin, MT recovery after drug-induced depolymerization was impaired. Similarly, immunodepletion of -tubulin from Arabidopsis extracts severely compromised in vitro polymerization of MTs. Reduction of -tubulin protein levels led to randomization and bundling of cortical MTs. This finding indicates that MT-bound -tubulin is part of a cortical template guiding the microtubular network and is essential for MT nucleation. Furthermore, we found that cells with decreased levels of -tubulin could progress through mitosis, but cytokinesis was strongly affected. Stepwise diminution of -tubulin allowed us to reveal roles for MT nucleation in plant development, such as organization of cell files, anisotropic and polar tip growth, and stomatal patterning. Some of these functions of -tubulin might be independent of MT nucleation.
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