An auxin-driven polarized transport model for phyllotaxis

doi:10.1073/pnas.0509839103

An auxin-driven polarized transport model for phyllotaxis

^*Computational Biology and Biological Physics Group, Department of Theoretical Physics, Lund University, S-221 00 Lund, Sweden; ^‡Division of Biology and ^§Biological Network Modeling Center, California Institute of Technology, Pasadena, CA 91125; and ^∥Institute of Genomics and Bioinformatics and Department of Computer Science, University of California, Irvine, CA 92697

Contributed by Elliot M. Meyerowitz, November 12, 2005

Abstract

Recent studies show that plant organ positioning may be mediated by localized concentrations of the plant hormone auxin. Auxin patterning in the shoot apical meristem is in turn brought about by the subcellular polar distribution of the putative auxin efflux mediator, PIN1. However, the question of what signals determine PIN1 polarization and how this gives rise to regular patterns of auxin concentration remains unknown. Here we address these questions by using mathematical modeling combined with confocal imaging. We propose a model that is based on the assumption that auxin influences the polarization of its own efflux within the meristem epidermis. We show that such a model is sufficient to create regular spatial patterns of auxin concentration on systems with static and dynamic cellular connectivities, the latter governed by a mechanical model. We also optimize parameter values for the PIN1 dynamics by using a detailed auxin transport model, for which parameter values are taken from experimental estimates, together with a template consisting of cell and wall compartments as well as PIN1 concentrations quantitatively extracted from confocal data. The model shows how polarized transport can drive the formation of regular patterns.

Footnotes

↵ ¶ To whom correspondence may be addressed. E-mail: emj{at}uci.edu or meyerow{at}caltech.edu.
↵ † H.J. and M.G.H. contributed equally to this work.
Author contributions: H.J., M.G.H., B.E.S., E.M.M., and E.M. designed research; H.J., M.G.H., B.E.S., and E.M. performed research; H.J., M.G.H., B.E.S., E.M.M., and E.M. analyzed data; and H.J. and M.G.H. wrote the paper.
Conflict of interest statement: No conflicts declared.
Freely available online through the PNAS open access option.