Integrative Model of root hair growth stages (IMAGE)
Caption
A phenotypic model based on microscopic observations is represented on the left, the dynamic mathematical model rendering on the right. Endoplasmic microtubules (EMTs) (centre of the cell) and cortical microtubules (CMTs) (cell periphery) are represented as green lines on the left. Actin filaments (AFs) are represented as yellow lines.
Late FG: Based on the dynamics of cytoskeleton fluorescence intensity (left), our model (right) shows that the AFs forces have their larger effect in connecting the nucleus to the tip (Modelling, yellow lines). These AF forces between the back of the nucleus and the centre of AF effects (yellow dashed line) at the front create compression forces resulting in nucleus squeezing, thus reducing nuclear apparent aspect ratio.
Early SG: MT fluorescence intensity decreases during the FG/SG transition (Experimental, green lines), resulting in the MT fringe disappearance and an overall decrease of the MT fluorescence signal (thinner green lines), while the AF fluorescence intensity peak follows the nuclear position (Experimental, yellow lines). Vacuole position shifts to the subapical region together with a transient bulging at the subapical region resulting in an increase of RH apparent young modulus. In our model the nucleus moving forward is the result of decreasing MT forces no longer counterbalancing AF forces as well as reduced TGR, thus resulting in its stabilisation to the front of the centre of effects of AFs (Modelling, yellow dashed line). Our experiments also further suggest an implication of MTs to maintain the nucleus connection to the tip.
Late SG: Our model displays an increase of the nucleus aspect ratio from nucleus internal forces (red arrows) counterbalancing the reduction in AF compression forces during late SG/EM transition. The vacuole progressively invades the subapical space.
Early M: AF bundling up to the tip triggers tip growth arrest (included in our simulation of reduced TGR to the maximum, dark green colour at the tip). Following this, the nucleus reaches its maximal elongation, supported by nucleoskeleton and AF forces. EMTs have disappeared resulting in a full disconnection of the nucleus from the tip. AF backwards forces then start to lead the nucleus back towards the RH base. The vacuole reaches the very tip, indicative of the Early M stage.
Credit
Gilles Dupouy and Tamsin Spelman
Usage Restrictions
Please only republished in reference to the research paper published in The Plant Cell and include credit to Gilles Dupouy and Tamsin Spelman.
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Original content