title: Modelling of Arabidopsis LAX3 expression suggests auxin homeostasis.
abstract: Emergence of new lateral roots from within the primary root in Arabidopsis has been shown to be regulated by the phytohormone auxin, via the expression of the auxin influx carrier LAX3, mediated by the ARF7/19 IAA14 signalling module (Swarup et al., 2008). A single cell model of the LAX3 and IAA14 auxin response was formulated and used to demonstrate that hysteresis and bistability may explain the experimentally observed 'all-or-nothing' LAX3 spatial expression pattern in cortical cells containing a gradient of auxin concentrations. The model was tested further by using a parameter fitting algorithm to match model output with qRT-PCR mRNA expression data following exogenous auxin treatment. It was found that the model is able to show good agreement with the data, but only when the exogenous auxin signal is degraded over time, at a rate higher than that measured in the experimental medium, suggesting the triggering of an endogenous auxin homeostasis mechanism. Testing the model over a more physiologically relevant range of extracellular auxin shows bistability and hysteresis still occur when using the optimised parameters, providing the rate of LAX3 active auxin transport is sufficiently high relative to passive diffusion.
authors.affiliation: Centre for Plant Integrative Biology, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, UK.
authors.forename: Nathan
authors.initials: N
authors.lastname: Mellor
authors.affiliation: Centre for Plant Integrative Biology, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, UK; Unite Mixte de Recherche 7265, Commissariat à L׳Energie Atomique et aux Energies Alternatives, Centre National de la Recherche Scientifique, Aix-Marseille Université, Laboratoire de Biologie du Developpement des Plantes, Saint-Paul-lez-Durance, France.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Péret
authors.affiliation: Centre for Plant Integrative Biology, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, UK.
authors.forename: Silvana
authors.initials: S
authors.lastname: Porco
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Ilkka
authors.initials: I
authors.lastname: Sairanen
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Karin
authors.initials: K
authors.lastname: Ljung
authors.affiliation: Centre for Plant Integrative Biology, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, UK.
authors.forename: Malcolm
authors.initials: M
authors.lastname: Bennett
authors.affiliation: Centre for Plant Integrative Biology, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, UK; School of Mathematical Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
authors.forename: John
authors.initials: J
authors.lastname: King
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003198:Computer Simulation; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000494:pharmacology; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; C531125:LAX3 protein, Arabidopsis; D026901:Membrane Transport Proteins; D012333:RNA, Messenger
keywords: Auxin degradation; Mathematical modelling; Plant lateral root development