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VENUSphotobleachingdecay

VENUS > ∅

VENUSproduction

∅ > VENUS

auxin_TIR1_VENUSassociation

auxinTIR1 + VENUS > auxinTIR1VENUS

auxin_TIR1_VENUSdissociation

auxinTIR1VENUS > auxinTIR1 + VENUS

auxin_TIR1_VENUSdissociationleadingtoubiquitination

auxinTIR1VENUS > auxinTIR1

auxin_TIR1association

auxin + TIR1 > auxinTIR1

auxin_TIR1dissociation

auxinTIR1 > auxin + TIR1

auxindecay

auxin > ∅

auxinproduction

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Root gravitropism is regulated by a transient lateral auxin gradient controlled by a tipping-point mechanism.

  • Leah R Band
  • Darren M Wells
  • Antoine Larrieu
  • Jianyong Sun
  • Alistair M Middleton
  • Andrew P French
  • Géraldine Brunoud
  • Ethel Mendocilla Sato
  • Michael H Wilson
  • Benjamin Péret
  • Marina Oliva
  • Ranjan Swarup
  • Ilkka Sairanen
  • Geraint Parry
  • Karin Ljung
  • Tom Beeckman
  • Jonathan M Garibaldi
  • Mark Estelle
  • Markus R Owen
  • Kris Vissenberg
  • T Charlie Hodgman
  • Tony P Pridmore
  • John R King
  • Teva Vernoux
  • Malcolm J Bennett
Proc. Natl. Acad. Sci. U.S.A. 2012; 109 (12): 4668-4673
Abstract
Gravity profoundly influences plant growth and development. Plants respond to changes in orientation by using gravitropic responses to modify their growth. Cholodny and Went hypothesized over 80 years ago that plants bend in response to a gravity stimulus by generating a lateral gradient of a growth regulator at an organ's apex, later found to be auxin. Auxin regulates root growth by targeting Aux/IAA repressor proteins for degradation. We used an Aux/IAA-based reporter, domain II (DII)-VENUS, in conjunction with a mathematical model to quantify auxin redistribution following a gravity stimulus. Our multidisciplinary approach revealed that auxin is rapidly redistributed to the lower side of the root within minutes of a 90° gravity stimulus. Unexpectedly, auxin asymmetry was rapidly lost as bending root tips reached an angle of 40° to the horizontal. We hypothesize roots use a "tipping point" mechanism that operates to reverse the asymmetric auxin flow at the midpoint of root bending. These mechanistic insights illustrate the scientific value of developing quantitative reporters such as DII-VENUS in conjunction with parameterized mathematical models to provide high-resolution kinetics of hormone redistribution.
The SBML for this model was obtained from the BioModels database (BioModels ID: BIOMD0000000413) Biomodels notes: Figure s15 in the supplementary material of the reference publication has been reproduced here. Figure E in the curation figure also corresponds to Figure 2A of the reference publication. The model as such corresponds to the auxin dose of 10nM (cyan line in the plot). Different auxin doses are incorporated in the model using the parameter, alpha_tr. alpha_tr = 5.83 (no auxin) alpha_tr = 7.44 (1nM) alpha_tr = 19.96 (5nM) alpha_tr = 30.50 (10nM) alpha_tr = 132.82 (100nM) alpha_tr = 270.52 (1000nM). The model was simulated using Copasi v4.8 (Build 35). JWS Online curation: This model was curated by reproducing the Figure S15A.