Arabidopsis GCP2 and GCP3 are part of a soluble gamma-tubulin complex and have nuclear envelope targeting domains.
In higher plants, microtubules (MTs) are assembled in distinctive arrays in the absence of a defined organizing center. Three MT nucleation sites have been described: the nuclear surface, the cell cortex and cortical MT branch points. The Arabidopsis thaliana (At) genome contains putative orthologues encoding all the components of characterized mammalian nucleation complexes: gamma-tubulin and gamma-tubulin complex proteins GCP2 to GCP6. We have cloned the cDNA encoding AtGCP2, and show that gamma-tubulin, AtGCP2 and AtGCP3 are part of the same tandem affinity-purified complex and are present in a large membrane-associated complex. In addition, small soluble gamma-tubulin complexes of the size expected for a gamma-tubulin core complex are recruited to isolated nuclei. Using immunogold labelling, AtGCP3 is localized to both the nuclear envelope (NE) and the plasma membrane. To identify domains that could play a role in targeting complexes to these nucleation sites, truncated AtGCP2- and AtGCP3-green fluorescent protein fusion proteins were expressed in BY-2 cells. Several domains from AtGCP2 and AtGCP3 are capable of targeting fusions to the NE. We propose that regulated recruitment of soluble gamma-tubulin-containing complexes is responsible for nucleation at dispersed sites in plant cells and contributes to the formation and organization of the various MT arrays.
Seltzer
Virginie
V
Institut de Biologie Moléculaire des Plantes, UPR2357-CNRS, Université Louis Pasteur, 12 rue du Général Zimmer, 67084 Strasbourg cedex, France.
Janski
Natacha
N
Canaday
Jean
J
Herzog
Etienne
E
Erhardt
Mathieu
M
Evrard
Jean-Luc
JL
Schmit
Anne-Catherine
AC
D017360:Arabidopsis / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009685:Nuclear Envelope / Q000378:metabolism*; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012995:Solubility; D014026:Nicotiana; D014404:Tubulin / Q000378:metabolism*
D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D021382:Protein Sorting Signals; D014404:Tubulin