title: Morphogengineering roots: comparing mechanisms of morphogen gradient formation.
abstract: BACKGROUND
  In developmental biology, there has been a recent focus on the robustness of morphogen gradients as possible providers of positional information. It was shown that functional morphogen gradients present strong biophysical constraints and lack of robustness to noise. Here we explore how the details of the mechanism which underlies the generation of a morphogen gradient can influence those properties.
  
  
  RESULTS
  We contrast three gradient-generating mechanisms, (i) a source-decay mechanism; and (ii) a unidirectional transport mechanism; and (iii) a so-called reflux-loop mechanism. Focusing on the dynamics of the phytohormone auxin in the root, we show that only the reflux-loop mechanism can generate a gradient that would be adequate to supply functional positional information for the Arabidopsis root, for biophysically reasonable kinetic parameters.
  
  
  CONCLUSIONS
  We argue that traits that differ in spatial and temporal time-scales can impose complex selective pressures on the mechanism of morphogen gradient formation used for the development of the particular organism.
authors.affiliation: Computational & Systems Biology, John Innes Centre, Norwich Research Park, Norwich, NR4 7UH, UK. veronica.grieneisen@jic.ac.uk
authors.forename: Verônica A
authors.initials: VA
authors.lastname: Grieneisen
authors.forename: Ben
authors.initials: B
authors.lastname: Scheres
authors.forename: Paulien
authors.initials: P
authors.lastname: Hogeweg
authors.forename: Athanasius F
authors.initials: AF
authors.lastname: M Marée
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000378:metabolism; D001692:Biological Transport; D055592:Biophysical Phenomena; D007210:Indoleacetic Acids / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D018517:Plant Roots / Q000166:cytology* / Q000378:metabolism*; D062211:Spatio-Temporal Analysis
chemical_list: D007210:Indoleacetic Acids