Actin Counters Geometry to Guide Plant Cell Division

Camila Goldy, Samantha Moulin, Yutaro Shimizu, Guillaume Cerutti, Vincent Bayle, Magali Grison, Yvon Jaillais, David Bouchez, Yohann Boutté, Martine Pastuglia, Philippe Andrey, Marie-Cécile Caillaud

Posted on: 26 November 2025 , updated on: 27 November 2025

Preprint posted on 22 August 2025

When geometry isn’t enough, actin helps plant cells decide where to divide, ensuring robust tissue patterning

Selected by Jeny Jose

Categories: cell biology, plant biology

Why this research is important

Plant morphogenesis depends on precisely oriented cell divisions rather than cell migration. Goldy and team uncover a central role for F-actin as a cortical landmark that maintains division plane fidelity and allows cells to integrate mechanical and positional signals.

When actin is intact, cells can “override” purely geometric predictions to align divisions with developmental context. When actin is disrupted, they revert to basic geometric rules, revealing that actin endows plant cells with morphogenetic flexibility.

This work reframes actin as a key player in the spatial coordination of plant growth, working alongside microtubules to maintain tissue integrity in a rigid, immobile system.

Background

In multicellular organisms, the orientation of cell division is a key determinant of tissue architecture and cell fate. In plants, this orientation defines whether daughter cells divide symmetrically or asymmetrically, shaping organ structure. Because plant cells are encased by rigid cell walls and lack centrosomes, they cannot round up like animal cells and must rely on cytoskeletal mechanisms to position their division plane precisely.

Traditionally, the microtubule-based preprophase band (PPB) marks the future division site, while the phragmoplast later guides the new cell plate to this cortical location. However, mutants lacking PPBs often show surprisingly mild defects, suggesting additional mechanisms cooperate to ensure correct division orientation.

Microtubules and actin filaments reorganize throughout mitosis to guide cell division. In prophase, a microtubule-rich preprophase band marks the future division plane. Microtubules then form the mitotic spindle to separate chromosomes, while actin supports nuclear positioning and cytoskeletal changes.

While geometric rules, like the shortest wall, minimal surface area principle, can predict many plant divisions, they fail to explain all observed orientations. Increasing evidence points to the actin cytoskeleton (F-actin) as a critical but less understood player. In the preprint highlighted here, Goldy and colleagues use the Arabidopsis root epidermis to uncover how actin enables cells to integrate geometry, mechanics, and identity to achieve robust division orientation.

Key results

1. Cell-type-specific division behaviour

The Arabidopsis root epidermis contains two distinct cell types:

Trichoblasts: root-hair producing cells
Atrichoblasts: non–hair-producing cells

Using 3D imaging and geometric modelling, the authors found that atrichoblasts typically divide along the predicted minimal-surface plane, while trichoblasts frequently deviate, dividing perpendicular to geometric expectations. This demonstrates that cell identity modulates division orientation, integrating more than simple geometry.

2. Directional growth reduces dependence on the PPB

In the PPB-deficient trm678 mutant, average division angles remained near 90° relative to the root axis, though variability increased, particularly in atrichoblasts. Separating cell types revealed that PPB loss disrupted the geometry-driven rules in atrichoblasts more than in trichoblasts with random anchoring along the lateral cell surface, suggesting additional factors affecting variability.

3. Actin guides division orientation and cooperates with microtubules to stabilise it

In PPB-deficient mutants, division planes may tilt, but they almost always remain anchored to the cell’s lateral sides. This consistency hints that other molecular systems act as “backup safeguards,” ensuring the division plane doesn’t form on the wrong faces of the cell. One likely candidate is the actin cytoskeleton, which influences cell shape, the positioning of tricellular junctions, and the precision of the division site. Actin filaments also accumulate at the apicobasal faces of dividing cells, hinting that they might help stabilise or translate the positional cues normally provided by microtubules.

Disrupting F-actin using Latrunculin B (LatB) or Cytochalasin D erased apicobasal actin enrichment and caused pronounced misoriented divisions, especially in trichoblasts. Under actin disruption (or in the act7-4 mutant), both trichoblasts and atrichoblasts reverted to purely geometric division orientations, as if “defaulting” to the shortest-path rule. These experiments reveal that actin normally allows cells to override geometric predictions, integrating developmental and positional cues to achieve correct orientation.

In trm678 mutants treated with LatB, division planes became almost random, and cells lost their alignment with the organ’s growth axis. This reveals that actin provides an essential layer of control, allowing cells to maintain correct division orientation even when the PPB is absent or unreliable. The PPB sets the spatial “blueprint” for division, while actin maintains and stabilises that orientation through the mechanical stages of mitosis.

4. Actin anchors spindles to maintain orientation

Microscopy revealed that actin disruption decoupled cortical division zone (CDZ) markers from phragmoplast guidance. Spindle poles in LatB-treated or act7-4 mutants became misaligned, tilting toward apicobasal faces. This indicates that actin filaments anchor the spindle apparatus to the cortex, maintaining orientation despite geometric pressures.

Glossary

PPB (Preprophase band): A transient ring of microtubules and actin that marks the future division site before mitosis.
Phragmoplast: A plant-specific structure made of microtubules, actin, and membranes that guides new cell wall formation during cytokinesis.
Trichoblast / Atrichoblast: Two epidermal cell types in the Arabidopsis root; trichoblasts form root hairs, while atrichoblasts do not.
LatB / CytD: Latrunculin B and Cytochalasin D, chemical inhibitors that disrupt actin polymerisation.
CDZ (Cortical Division Zone): The region at the cell cortex where the new cell wall will attach.
Apicobasal axis: The axis running from the tip (apical) to the base (basal) of a cell or tissue; in plant cells, it defines the polarity and orientation of growth and division.

Tags: actin, cellgeometry, plantcell, plantmorphogenesis, roothair

doi: https://doi.org/10.1242/prelights.42163

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