Distribution of γ-Tubulin in Higher Plant Cells: Cytosolic γ-Tubulin is Part of High Molecular Weight Complexes

Abstract

γ-Tubulin is a protein found in all eukaryotic cells, where it plays a key role in the nucleation of microtubules. In higher plant cells, γ-tubulin is localized at the nuclear surface, a known microtubule-organizing centre, and is codistributed with all microtubule arrays. Functions of plant γ-tubulin remain to be determined. This study describes some properties of higher plant γ-tubulin. The overall level of γ-tubulin was constant during the cell cycle in synchronized tobacco BY-2 cells. Biochemical analysis of the subcellular distribution of γ-tubulin in maize cells revealed that, in contrast with animal γ-tubulin, plant γ-tubulin is mainly associated with endomembranes. We showed for the first time that the pool of soluble cytosolic γ-tubulin contained two main γ-tubulin complexes. γ-tubulin, Hsp70 and TCP1-related proteins might interact in a small complex of 750 kDa. A second γ-tubulin complex, larger than 1500 kDa was purified. The protein profile of this large complex was very similar to animal γ-tubulin complexes. The putative functions of these two complexes in plant microtubule nucleation are discussed.

Abbreviations

γTuRC: γ-tubulin ring complex

Hsp: heat shock protein

MTOC: microtubule organizing centre

SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis

SPB: spindle pole body

TCP1: T-complex polypeptide 1

Key words

Higher plants - microtubule nucleation - γ-tubulin - γTuRC - MTOC

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Section Editor: A. M. C. Emons