Kamamoto, N. | bioRxiv Science

bioRxiv2026

3D geometry and mechanics of a single apical stem cell ensure helically symmetric plant body in multicellular models

Self-renewing divisions of stem cells at the growing tip universally govern plant development. In basal land plants, a single apical stem cell (AC) undergoes successive 120-degree rotational divisions while maintaining a self-similar tetrahedral geometry with three division walls, recapitulating the helically symmetric body architecture. The mechanisms by which AC geometry and mechanics determine the division axis and its rotation are largely unknown. Here, we develop two 3D multicellular mathematical models to address these questions. Our geometrical model reveals that the least area rule, coordinated with the AC surface curvature, is sufficient to drive rotational divisions by rotating the geometric proportion of the AC. Furthermore, by incorporating biologically plausible cell growth mechanics, we show that the tetrahedral AC and its rotational division spontaneously emerge from a spherical cell. Notably, the maximal tension rule confers superior robustness against stochastic fluctuations in division orientation compared to the least area rule, because the sequential formation of division walls continuously updates the tension distribution to guide subsequent orientation. These results suggest that the tetrahedral AC and the helically symmetric body plan are natural consequences of self-renewing cell divisions, imposed by 3D geometry and/or mechanics.

plant biology↗

bioRxiv2024

HD-ZIP IV genes are essential for embryo initial cell polarization in the radial axis initiation in Arabidopsis

Plants develop along apical-basal and radial axes. In Arabidopsis thaliana, the radial axis becomes evident when the cells of the eight-cell proembryo divide periclinally, forming inner and outer cell layers. Although changes in cell polarity or morphology likely precede this oriented cell division, the initial events and the factors regulating radial axis formation remain elusive. Here, we report that three transcription factors belonging to class IV homeodomain-leucine zipper (HD-ZIP IV) family redundantly regulate radial pattern formation: HOMEODOMAIN GLABROUS11 (HDG11), HDG12, and PROTODERMAL FACTOR2 (PDF2). The hdg11 hdg12 pdf2 triple mutant failed to undergo periclinal division at the eight-cell stage and cell differentiation along the radial axis. Live-cell imaging revealed that this failure in radial axis formation can be traced back to the behavior of the embryo initial cell (apical cell), which is generated by zygote division. In the wild type, the apical cell grows longitudinally and then radially and its nucleus remains at the bottom of the cell, where the vertical cell plate emerges. By contrast, the mutant apical cell elongates longitudinally and its nucleus releases from its basal position, resulting in a transverse division. Computer simulations based on the live-cell imaging data confirmed the importance of the geometric rule (the minimal plane principle and nucleus-passing principle) in determining the cell division plane. We propose that HDG11, HDG12, and PDF2 promote apical cell polarization, i.e., radial cell growth and basal nuclear retention, as the initial event of radial axis formation during embryogenesis.

plant biology↗