Poster: Cytoskeleton: Structure & Function

Abs # 1115: g-tubulin is essential for cortical microtubule assembly

Presenter:	Murata, Takashi , tkmurata@nibb.ac.jp
Authors	Murata, Takashi  (A)   Hori, Koichi  (B)   Watanabe, Yuichiro  (B)   Hasebe, Mitsuyasu  (A)
Affiliations:	(A): National Institute for Basic Biology (B): Department of Life Scienecs, Graduate School of Arts and Sciences, The University of Tokyo

Microtubules in animal and yeast cells are nucleated at microtubule organizing centers (MTOC) such as centrosome and spindle pole body, respectively. Microtubules in plant cells nucleate at the nuclear envelope before and after mitosis, but assemble along the plasma membrane without any visible structures of MTOC at interphase. The cortical microtubules are unique cytoskeletal structures in green plants and regulate direction of cell expansion. We have analyzed mechanism of microtubule nucleation in the cortical cytoplasm of plant cells. g-tubulin plays a central role of microtubule nucleation in MTOCs of animal and yeast cells. We showed that g-tubulin localizes at the end of cortical microtubules, and hypothesized that components of MTOCs disperse in the cortical cytoplasm of plant cells and nucleate cortical microtubules. At the first step to evaluate the hypothesis, we analyzed the effects of virus-induced gene silencing of g-tubulin on cortical microtubule formation, because involvement of g-tubulin in cortical microtubule nucleation is still hypothetical. Nicotiana benthamiana plants were infected with a tomato mosaic virus vector harboring partial g-tubulin mRNA sequence. The virus triggered virus-induced gene silencing and amount of g-tubulin greatly decreased in the leaves that expanded after infection. The leave had malformed epidermal cells with loss of cortical microtubules. The infected plants continued to grow, probably because viruses did not enter into the apical meristem. Control viruses without g-tubulin mRNA sequence had no effect. These results indicate that g-tubulin is essential for cortical microtubule assembly. Factors that localize g-tubulin to cortical cytoplasm should be identified at the next step of study.