In many plants, a zygote (fertilized egg) undergoes asymmetric cell division to establish the apical-basal (up-down) body axis that will eventually connect the future flower and roots. However, how the zygote determines this up-down orientation has remained largely unknown.
A research group made up of Graduate Student Sakumi Nakagawa, Assistant Professor Hikari Matsumoto, Graduate Student Yuga Hanaki (at the time of the research), and Professor Minako Ueda of the Graduate School of Life Sciences at Tohoku University; Postdoctoral Researcher Zichen Kang (at the time of the research; currently at Akita Prefectural University) and Associate Professor Satoru Tsugawa (at the time of the research; currently at Akita Prefectural University) of the Graduate School of Engineering at Hokkaido University; Researcher Tomonobu Nonoyama (at the time of the research; currently at Akita Prefectural University) of the Graduate School of Engineering at Kobe University; and Professor Yukitaka Ishimoto of the Faculty of Science and Engineering at Saga University has discovered a precise feedback loop governing this process: as the zygote elongates upward (vertically), the tension on the cell surface increases, triggering microtubules to assemble into a band-like "frame" that constricts the cell. This constriction prevents the zygote from expanding horizontally, thereby forcing it to continue growing vertically. This research clarified an elaborate strategy in which a zygote utilizes mechanical feedback to automatically sustain its growth. The findings were published in the early access edition of Nature Communications.
(B) A schematic diagram of the mechanical feedback between cell growth and microtubules identified in this study.
Provided by Tohoku University
To investigate how the apical-basal axis is established, the group performed high-precision live imaging of zygote dynamics up to the point of asymmetric division, using Arabidopsis thaliana as a model plant.
Upon fertilization, the zygote begins growing upward (vertically). Microtubules then gather around this expanding region, forming a "microtubule band." To understand how these microtubules assemble, the team constructed a mechanical simulation model (an elasto-plastic deformation model) that precisely replicated the growing zygote. The simulation predicted that surface tension increases specifically at the location where the cell expands. This region perfectly matched the site where the microtubule band forms. Furthermore, when cell growth was intentionally halted to prevent the increase in surface tension, the microtubule band failed to assemble. These findings prove that the microtubule band is generated by natural mechanical shifts, specifically, the rise in surface tension caused by cell growth.
Conversely, when the researchers disrupted the microtubule band, the zygote expanded horizontally instead of vertically. This demonstrated that the microtubules act as a mechanical "frame" that constricts the tip of the zygote, effectively guiding its vertical growth. In short, a mechanical feedback loop exists where vertical growth and microtubule band formation are mutually dependent, allowing the zygote to automatically and continuously elongate in the vertical direction.
Furthermore, the study revealed that this microtubule band dictates the positioning of the subsequent cell division plane, leading directly to the asymmetric division that establishes the plant's apical-basal axis.
This study has unveiled a sophisticated yet simple strategy: by growing vertically, the zygote induces its own mechanical changes, which are then sensed by microtubules to autonomously control growth and division. Moving forward, identifying exactly how microtubules perceive surface tension and what triggers the initial vertical growth will significantly advance our understanding of how plant organisms take shape.
This research was undertaken with support from JST's CREST program (JPMJCR2121).
Journal Information
Publication: Nature Communications
Title: Temporal changes in surface tension guide microtubule organization and accurate asymmetric division of Arabidopsis zygotes
DOI: 10.1038/s41467-026-72280-4
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.