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Vol. 19, Issue 10, 4534-4544, October 2008

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Two Microtubule-associated Proteins of Arabidopsis MAP65s Promote Antiparallel Microtubule Bundling

Jérémie Gaillard^*,, Emmanuelle Neumann^,, Daniel Van Damme^,||, Virginie Stoppin-Mellet^*, Christine Ebel, Elodie Barbier^*, Danny Geelen^¶, and Marylin Vantard^*

*Institut de Recherches en Technologies et Sciences pour le Vivant, Unité Mixte de Recherche, Centre National de la Recherche Scientifique, Centre d'Energie Atomique, Institut de Recherche Agronomique, Université Joseph Fourier, 38054 Grenoble, France; Institut de Biologie Structurale J.-P. Ebel, UMR 5075 CNRS, CEA, Université Joseph Fourier, 38027 Grenoble, France; Department of Plant Systems Biology, Flanders Institute for Biotechnology, B-9052 Ghent, Belgium; ^||Department of Molecular Genetics, Ghent University, B-9052 Ghent, Belgium; and ^¶Department of Plant Production, Ghent University, B-9000 Ghent, Belgium

Submitted April 3, 2008; Revised July 17, 2008; Accepted July 18, 2008
Monitoring Editor: David G. Drubin

The Arabidopsis MAP65s are a protein family with similarity to the microtubule-associated proteins PRC1/Ase1p that accumulate in the spindle midzone during late anaphase in mammals and yeast, respectively. Here we investigate the molecular and functional properties of AtMAP65-5 and improve our understanding of AtMAP65-1 properties. We demonstrate that, in vitro, both proteins promote the formation of a planar network of antiparallel microtubules. In vivo, we show that AtMAP65-5 selectively binds the preprophase band and the prophase spindle microtubule during prophase, whereas AtMAP65-1-GFP selectively binds the preprophase band but does not accumulate at the prophase spindle microtubules that coexists within the same cell. At later stages of mitosis, AtMAP65-1 and AtMAP65-5 differentially label the late spindle and phragmoplast. We present evidence for a mode of action for both proteins that involves the binding of monomeric units to microtubules that "zipper up" antiparallel arranged microtubules through the homodimerization of the N-terminal halves when adjacent microtubules encounter.

These authors contributed equally to this work.

Address correspondence to: Marylin Vantard (marylin.vantard{at}cea.fr)

Abbreviations used: CMT, cortical microtubule; AtMAP65, Arabidopsis thaliana microtubule-associated protein 65; GFP, green fluorescent protein; MT, microtubules.