Critical threshold for microtubule amplification through templated severing

TL;DR

This study models microtubule amplification via templated severing in plant cells, revealing a critical rescue probability threshold for amplification in bounded growth regimes and elucidating factors influencing reorientation speed.

Contribution

It introduces a dynamic one-dimensional model for microtubule amplification through templated severing, highlighting the role of rescue probability in different growth regimes.

Findings

Amplification occurs without rescue probability in unbounded growth but is affected by it.

A critical rescue probability threshold exists for amplification in bounded growth.

The analytical theory accurately predicts the critical rescue probability value.

Abstract

The cortical microtubule array of dark-grown hypocotyl cells of plant seedlings undergoes a striking, and developmentally significant, reorientation upon exposure to light. This process is driven by the exponential amplification of a population of longitudinal microtubules, created by severing events localized at crossovers with the microtubules of the pre-existing transverse array. We present a dynamic one-dimensional model for microtubule amplification through this type of templated severing. We focus on the role of the probability of immediate rescue-after-severing of the newly-created lagging microtubule, observed to be a characteristic feature of the reorientation process. Employing stochastic simulations, we show that in the dynamic regime of unbounded microtubule growth, a finite value of this probability is not required for amplification to occur, but does strongly influence the degree of amplification, and hence the speed of the reorientation process. In contrast, in the regime of bounded microtubule growth, we show that amplification only occurs above a critical threshold. We construct an approximate analytical theory, based on a priori limiting the number of crossover events considered, which allows us to predict the observed critical value of the rescue-after-severing probability with reasonable accuracy.