Microtubule-Organizing Centers and Nucleating Sites in Land Plants

Expression of Arabidopsis γ-Tubulin in Fission Yeast Reveals Conserved and Novel Functions of γ-Tubulin

“…This overlap has been observed in every type of microtubule array of plant cells, including mitotic spindles, cortical mi- crotubules, phragmoplasts, and preprophase bands. The possibility that ␥-tubulin functions along microtubules, or even incorporates into the lattice of the microtubule, has been proposed based on these observations (Liu et al, 1993;Vaughn and Harper, 1998;Canaday et al, 2000). However, our results indicate that Arabidopsis ␥-tubulin has no tendency to stick to or to be incorporated into the microtubules of S. .…”

“…This finding demonstrated that ␥-tubulin is functionally conserved in phylogenetically distant organisms with microtubule-organizing centers (MTOCs) that differ vastly in size and appearance. However, the spindles of these species do share the common feature that microtubules extend from discrete MTOCs, spindle pole bodies (SPBs) in fungi, and centrosomes in higher animal cells.In contrast, in plant cells, spindle microtubules are less focused than in typical animal cells and no discrete MTOCs equivalent to the centrosomes in animal cells are present (for review, see Vaughn and Harper, 1998; Canaday et al, 2000;Wasteneys, 2002). The localization of ␥-tubulin in plant cells has been examined extensively (Liu et al, 1993(Liu et al, , 1994(Liu et al, , 1995 Binarova et al, 2000;Kumagai et al, 2003).…”

“…Although ␥-tubulin was sometimes enriched in regions containing the minus ends of the microtubules, it did not localize to, or help to define, MTOCs (Liu et al, 1993(Liu et al, , 1994 for review, see Joshi and Palevitz, 1996;Vaughn and Harper, 1998; Canaday et al, 2000). These observations gave rise to the hypothesis that ␥-tubulin in plants has functions along the microtubule array distinct from the nucleation of microtubules at the MTOCs (Liu et al, 1993;Vaughn and Harper, 1998; Canaday et al, 2000).To determine to what extent plant ␥-tubulin is functionally different from its animal or fungal counterparts, we expressed a flowering plant, Arabidopsis, ␥-tubulin (Liu et al, 1994) in the fission yeast S. pombe and determined whether it is able to function in place of the endogenous ␥-tubulin. We found that the Arabidopsis ␥-tubulin was able to support the growth of S. pombe at high temperatures.…”

“…In contrast, in plant cells, spindle microtubules are less focused than in typical animal cells and no discrete MTOCs equivalent to the centrosomes in animal cells are present (for review, see Vaughn and Harper, 1998;Canaday et al, 2000;Wasteneys, 2002). The localization of ␥-tubulin in plant cells has been examined extensively (Liu et al, 1993(Liu et al, , 1994(Liu et al, , 1995Binarova et al, 2000;Kumagai et al, 2003).…”

“…In most microtubule arrays of plant cells, ␥-tubulin is distributed along the microtubules, often in very small, punctate structures. Although ␥-tubulin was sometimes enriched in regions containing the minus ends of the microtubules, it did not localize to, or help to define, MTOCs (Liu et al, 1993(Liu et al, , 1994; for review, see Joshi and Palevitz, 1996;Vaughn and Harper, 1998;Canaday et al, 2000). These observations gave rise to the hypothesis that ␥-tubulin in plants has functions along the microtubule array distinct from the nucleation of microtubules at the MTOCs (Liu et al, 1993;Vaughn and Harper, 1998;Canaday et al, 2000).…”