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Proc Natl Acad Sci U S A. 2019 Feb 5;116(6):2338-2343. doi: 10.1073/pnas.1814160116. Epub 2019 Jan 16.

Polar vacuolar distribution is essential for accurate asymmetric division of Arabidopsis zygotes.

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Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602 Aichi, Japan.
Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, 630-0192 Nara, Japan.
Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwanoha, Kashiwa, 277-8562 Chiba, Japan.
International Research Organization for Advanced Science and Technology, Kumamoto University, Chuo-ku, 860-8555 Kumamoto, Japan.
Institute of Transformative Bio-Molecules, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601 Aichi, Japan.
Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Aichi, Japan.
National Institute for Basic Biology, Myodaiji, Okazaki, 444-8585 Aichi, Japan.
Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602 Aichi, Japan;


In most flowering plants, the asymmetric cell division of the zygote is the initial step in establishing the apical-basal axis of the mature plant. The zygote is polarized, possessing the nucleus at the apical tip and large vacuoles at the basal end. Despite their known polar localization, whether the positioning of the vacuoles and the nucleus is coordinated and what the role of the vacuole is in the asymmetric zygotic division remain elusive. In the present study, we utilized a live-cell imaging system to visualize the dynamics of vacuoles during the entire process of zygote polarization in Arabidopsis Image analysis revealed that the vacuoles formed tubular strands around the apically migrating nucleus. They gradually accumulated at the basal region and filled the space, resulting in asymmetric distribution in the mature zygote. To assess the role of vacuoles in the zygote, we screened various vacuole mutants and identified that shoot gravitropism2 (sgr2), in which the vacuolar structural change was impaired, failed to form tubular vacuoles and to polarly distribute the vacuole. In sgr2, large vacuoles occupied the apical tip and thus nuclear migration was blocked, resulting in a more symmetric zygotic division. We further observed that tubular vacuole formation and asymmetric vacuolar distribution both depended on the longitudinal array of actin filaments. Overall, our results show that vacuolar dynamics is crucial not only for the polar distribution along actin filaments but also for adequate nuclear positioning, and consequently zygote-division asymmetry.


Arabidopsis thaliana; apical–basal axis; live-cell imaging; vacuole; zygote

[Available on 2019-08-05]

Conflict of interest statement

The authors declare no conflict of interest.

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