Modeling the Aux/IAA Pathway Presentation by Labeed Ben-Ghaly

Overview: Motivation Background The Project Future Work

Motivation To provide provide a quantitative and cellular description of plant development

Confocal microscope, Zeiss LSM- 510

Phyllotaxis, pattern formation in plants New plant organs appear at the SAM in a remarkably symmetric fashion The spiral pattern and the connection to the Fibonacci series and Golden angle have attracted theoreticians Lots of models exist and new experimental data have illuminated molecular connections to the patterns

Introduction to Auxins Concentrations of the plant hormone Auxin play a major role in plant development.

How is Auxin activity regulated? Lateral inhibition between primordia. Reaction-diffusion inhibitor model. Depletion of primordium promoting factor. Jönsson H, et al 2006

Indole-3-acetic acid (IAA) Capable of creating new primordium when added to developing tissues. Reinhardt et al 2003 Aux/IAA

Modeling the Pathway Signal from older/incipient primordia Auxin flux Auxin concentration Simple model Active vs. Passive transport A - + H + AH

a i – auxin concentration P ij –PIN1 production degradation active transport passive transport Modeling the Pathway

Mathematica and xCellerator

T - active transport D - inactive transport Kd - degradation Analysis of Auxin Model Analysis predicts when the model will spontaneously create auxin peaks Also predicts distance between peaks

Animation, Simulation of Model

Concluding remarks Models can be used to indicate what players and interactions might be sufficient for driving phyllotaxis Experiments to test the auxin model

Thank-you SoCalBSI Bruce Shapiro Elliot Meyerowitz BNMC WaterTree NIH

References (2006) Mjolsness E. Modeling transcriptional regulation with equilibrium molecular complex composition, 5th International Conference on the Bioinformatics of Genome Regulation and Function (BGRS-2006), Volume 1, pp (2006) Jönsson H, Heisler M, Shapiro BE, Meyerowitz EM, Mjolsness ED. An Auxin-driven polarized transport model for phyllotaxis. Proc. Natl. Acad. Sci., U.S.A., 103(5): (2006) Alon, Uri An Introduction to Systems Biology: Design Principles of Biological Circuits. CRC