The dynamic behaviour of microtubules – which undergo frequent transitions between growth, shrinkage and pause states – is regulated by an array of microtubule-associated proteins (MAPs). For instance, the MAP215 proteins (including XMAP215 in Xenopus and CKAP5 in humans) have been proposed to promote both growth and shrinkage of microtubules, but aspects of their function remain unclear. On page 4114, Eiko Kawamura and Geoffrey O. Wasteneys investigate the in vivo role of MOR1, the Arabidopsis homologue of XMAP215. The authors have previously shown that, in the cells of a temperature-sensitive mor1 mutant, microtubule arrays are disrupted at the restrictive temperature; now, they investigate the dynamics of individual microtubules in mor1 cells. They first demonstrate that microtubule dynamics are reduced in the mor1 mutant, even at the permissive temperature. Moreover, both the growth and shrinkage rates of microtubules are dramatically reduced at the restrictive temperature, and the incidence and duration of pause events increases. The authors go on to show that the interaction of microtubules with the MAP EB1 is reduced at the restrictive temperature in the mor1 mutant. Thus, the role of MOR1 in microtubule organisation echoes that of its animal homologues.
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