RESUMO
Centrin - higher plants - MTOCs - microtubules nucleation In most eukaryotic cells, the Ca(2+)-binding protein centrin is associated with structured microtubule-organizing centers (MTOCs) such as centrosomes. In these cells, centrin either forms centrosome-associated contractile fibers, or is involved in centrosome biogenesis. Our aim was to investigate the functions of centrin in higher plant cells which do not contain centrosome-like MTOCs. We have cloned two tobacco BY-2 centrin cDNAs and we show that higher plant centrins define a phylogenetic group of proteins distinct from centrosome-associated centrins. In addition, tobacco centrins were found primarily associated with microsomes and did not colocalize with gamma-tubulin, a known MTOC marker. While the overall level of centrin did not vary during the cell cycle, centrin was prominently detected at the cell plate during telophase. Our results suggest that in tobacco, the major portion of centrin is not MTOC-associated and could be involved in the formation of the cell plate during cytokinesis.
Assuntos
Proteínas de Ligação ao Cálcio/análise , Centrossomo/metabolismo , Proteínas Cromossômicas não Histona , Microssomos/metabolismo , Nicotiana/química , Proteínas de Plantas/análise , Plantas Tóxicas , Sequência de Aminoácidos , Proteínas de Ligação ao Cálcio/química , Ciclo Celular , Clonagem Molecular , DNA Complementar/análise , Immunoblotting , Microscopia de Fluorescência , Dados de Sequência Molecular , Filogenia , Ligação Proteica , Isoformas de Proteínas , RNA Mensageiro/metabolismo , Homologia de Sequência de AminoácidosRESUMO
The structure and the molecular composition of the microtubule-organizing centers in acentriolar higher plant cells remain unknown. We developed an in vitro complementation assay where tobacco BY-2 extracts can restore the microtubule-nucleating activity of urea-inactivated mammalian centrosomes. Our results provide first evidence that soluble microtubule-nucleating factors are present in the plant cytosolic fraction. The implication for microtubule nucleation in higher plants is discussed.