GAMMA-TUBULINS AND THEIR FUNCTIONS IN PLANT CELLS

Higher plants represent an important group of eukaryotes where discrete sites for microtubule nucleation are absent in all mitotic and meiotic cells, and the concept of dispersed microtubule-nucleation sites has been generally accepted. Moreover, even in cells containing centrosomes or spindle pole bodies, microtubules can nucleate non-centrosomally but molecular mechanisms behind the process are so far poorly characterized. gamma-Tubulin is a ubiquitous phylogenetically conserved member of tubulin superfamily, present within the cells in various types of microtubule-organizing centers and cytoplasmic protein complexes. Down regulation of gamma-tubulin showed its essential role in non-centrosomal nucleation in plants. Plant gamma-tubulin is localized with all microtubule arrays, and in nuclei. Protein complexes of gamma-tubulin are present in soluble forms in cytoplasm and also with membranes. Association of gamma-tubulin complexes with microtubules and dynamic membranes might ensure the flexibility of non-centrosomal microtubule nucleation. However the presence of various molecular forms of gamma-tubulin Suggests that, in addition to its nucleation role, additional roles for non- centrosomal gamma-tubulin might exist.