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Modeling the emergence of polarity patterns for the intercellular transport of auxin in plants

Silvia Grigolon, Peter Sollich, Olivier C. Martin

plant-growthmorphogenesisauxincell-polaritypattern-formation

Abstract

The hormone auxin is actively transported throughout plants via protein machineries including the dedicated transporter known as PIN. The associated transport is ordered with nearby cells driving auxin flux in similar directions. Here we provide a model of both the auxin transport and of the dynamics of cellular polarisation based on flux sensing. Our main findings are: (i) spontaneous intracellular PIN polarisation arises if PIN recycling dynamics are sufficiently non-linear, (ii) there is no need for an auxin concentration gradient, and (iii) ordered multi-cellular patterns of PIN polarisation are favored by molecular noise.

Summary

This paper reveals a remarkable finding: cells can self-organize their polarity and create coordinated tissue-wide patterns even without pre-existing chemical gradients. The gradients emerge from the collective behavior.

Key insights on emergent gradient formation:

  1. Spontaneous polarization: Individual cells can spontaneously break symmetry and become polarized (having a “front” and “back”) through non-linear dynamics in PIN protein recycling.

  2. Flux sensing, not concentration sensing: Cells may sense auxin flux (flow through them) rather than absolute concentration. This creates a different type of gradient response.

  3. Emergent gradients: Rather than gradients directing tissue organization, ordered transport patterns can emerge from cellular noise and non-linear dynamics - the gradient is a consequence, not a cause.

  4. Coordinated tissue behavior: Once polarized, nearby cells align their transport directions, creating tissue-scale coordination from local rules.

  5. Role of noise: Molecular noise (random fluctuations) actually helps establish ordered patterns by allowing the system to explore different configurations.

This work shows that the relationship between gradients and tissue behavior is bidirectional - tissues both respond to gradients AND create them through their collective dynamics.

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