Nuclear -Tubulin during Acentriolar Plant Mitosis

Pavla Binarová^a, Vra Cenklová^b, Bettina Hause^c, Elena Kubátová^a, Martin Lysák^b, Jaroslav Doleel^b, László Bögre^d, and Pavel Dráber^e

^a Institute of Microbiology, Academy of Sciences of the Czech Republic, Vídnská 1083, 142 20 Prague 4, Czech Republic

^e Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Vídnská 1083, 142 20 Prague 4, Czech Republic

Correspondence to: Pavla Binarová, binarova{at}biomed.cas.cz (E-mail), 420-2-4752384 (fax)

Neither the molecular mechanism by which plant microtubules nucleate in the cytoplasm nor the organization of plant mitotic spindles, which lack centrosomes, is well understood. Here, using immunolocalization and cell fractionation techniques, we provide evidence that -tubulin, a universal component of microtubule organizing centers, is present in both the cytoplasm and the nucleus of plant cells. The amount of -tubulin in nuclei increased during the G₂ phase, when cells are synchronized or sorted for particular phases of the cell cycle. -Tubulin appeared on prekinetochores before preprophase arrest caused by inhibition of the cyclin-dependent kinase and before prekinetochore labeling of the mitosis-specific phosphoepitope MPM2. The association of nuclear -tubulin with chromatin displayed moderately strong affinity, as shown by its release after DNase treatment and by using extraction experiments. Subcellular compartmentalization of -tubulin might be an important factor in the organization of plant-specific microtubule arrays and acentriolar mitotic spindles.

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