Crosstalk complexities between auxin, cytokinin and ethylene in Arabidopsis root development: from experiments to systems modelling, and back again

Abstract

Understanding how hormones and genes interact to coordinate plant growth in a changing environment is a major challenge in plant developmental biology. Auxin, cytokinin and ethylene are three important hormones that regulate many aspects of plant development. This review critically evaluates the crosstalk between the three hormones in Arabidopsis root development. We integrate a variety of experimental data into a crosstalk network, which reveals multiple layers of complexity in auxin, cytokinin and ethylene crosstalk. In particular, data integration reveals an additional, largely overlooked link between the ethylene and cytokinin pathways, which acts through a phosphorelay mechanism. This proposed link addresses outstanding questions on whether ethylene application promotes or inhibits receptor kinase activity of the ethylene receptors. Elucidating the complexity in auxin, cytokinin and ethylene crosstalk requires a combined experimental and systems modelling approach. We evaluate important modelling efforts for establishing how crosstalk between auxin, cytokinin and ethylene regulates patterning in root development. We discuss how a novel methodology that iteratively combines experiments with systems modelling analysis is essential for elucidating the complexity in crosstalk of auxin, cytokinin and ethylene in root development. Finally, we discuss the future challenges from a combined experimental and modelling perspective.