Modelling Plant Hormone Gradients

Abstract Cellular patterning in the Arabidopsis root is coordinated via a localised auxin concentration maximum in the root tip, requiring the regulated expression of specific genes. The activities of plant hormones such as auxin, ethylene and cytokinin depend on cellular context and exhibit either synergistic or antagonistic interactions. Due to the complexity and nonlinearity of spatiotemporal interactions between both hormones and gene expression in root development, modelling plant hormone gradients requires a systems approach in which experimental data and modelling analysis are closely combined. Modelling therefore allows a predictive interrogation of highly complex and nonintuitive interactions between components in the system. Important factors to be considered when modelling hormone gradients include the construction of a hormonal crosstalk network, the formulation of kinetic equations and the construction of an in silico root map. A modelling approach enables the analysis of relationships between multiple hormone gradients, predictions on how hormone gradients emerge under the action of hormonal crosstalk, and the prediction and elucidation of experimental results from mutant roots. Key Concepts Patterning in Arabidopsis root development is coordinated via a localised auxin concentration maximum in the root tip, requiring the regulated expression of specific genes. The activities of plant hormones such as auxin, ethylene, cytokinin, abscisic acid, gibberellin and brassinosteroids depend on cellular context and exhibit either synergistic or antagonistic interactions. Auxin concentration and the associated regulatory and target genes are regulated by diverse interacting hormones and gene expression and therefore cannot change independently of the various crosstalk components in space and time. Other hormone concentrations, such as ethylene and cytokinin concentrations, and expression of the associated regulatory and target genes are also interlinked. Modelling plant hormone gradients requires a systems approach where experimental data and modelling analysis are closely combined. A hormonal crosstalk network describes the regulatory relationships between hormones and their associated genes. A kinetic equation can be formulated for any regulatory relationship following thermodynamic and kinetic principles. Construction of an in silico root map enables the study of multicellular cell–cell communications in Arabidopsis root development. Modelling hormone gradients enables the analysis of relationships between multiple hormone gradients, predictions on how hormone gradients emerge under the action of hormonal crosstalk, and the prediction and elucidation of experimental results from mutant roots. Modelling auxin gradients can also incorporate different mechanisms of polar auxin transport and the interaction of hormone gradients and root growth.