Tilted tubules

Researchers have long wondered how plants carry out microtubule nucleation, as they lack microtubule organizing centers. Takashi Murata, Matsuyasu Hasebe, and colleagues (National Institute for Basic Biology, Okazaki, Japan) now show that γ-tubulin promotes microtubule nucleation off of existing microtubules in higher plants. Moreover, new microtubules branch off from the sides, rather than the ends, of existing microtubules.

Plant cells form ordered microtubule arrays during interphase to enable cell shaping and orientation. To understand how these arrays form, Murata's group watched fluorescently labeled microtubules grow and shrink in live tobacco cells. They saw that all newly forming microtubules branched off either from existing tubules (at a 40° angle) or at a site where a microtubule had existed but then depolymerized only seconds earlier.

Using in vitro analysis, the team confirmed that already-established microtubules are required for...