Some fundamental aspects of modeling auxin patterning in the context of auxin-ethylene-cytokinin crosstalk.

The activities of hormones in the Arabidopsis root depend on cellular context and exhibit either synergistic or antagonistic interactions. Patterning in Arabidopsis root development is coordinated via a localized auxin concentration maximum in the root tip, mediating transcription of key regulatory genes. Auxin concentration and response are each regulated by diverse interacting hormones and gene expression and therefore cannot change independently of those hormones and genes. For example, experimental data accumulated over many years have shown that both ethylene and cytokinin regulate auxin concentration and response. Using the crosstalk of auxin-ethylene-cytokinin as a paradigm, we discuss the links between experimental data, reaction kinetics and spatiotemporal modeling to dissect hormonal crosstalk. In particular, we discuss how kinetic equations for modeling auxin concentration are formulated based on experimental data and also the underlying assumptions for deriving those kinetic equations. Furthermore, we show that, by integrating kinetic equations with spatial root structure, modeling of spatiotemporal hormonal crosstalk is a powerful tool for analyzing and predicting the roles of multiple hormone interactions in auxin patterning. Finally, we summarize important considerations in developing a spatiotemporal hormonal crosstalk model for plant root development.