Sending mixed messages: auxin-cytokinin crosstalk in roots

Despite their relatively simple appearance, roots are incredibly complex organs that are highly adapted to differing environments. Many aspects of root development are co-ordinated by subtle spatial differences in the concentrations of the phytohormones auxin and cytokinin. Events from the formation of a root during embryogenesis to the determination of the network of lateral roots are controlled by interactions between these hormones. Recently, interactions have been defined where auxin signaling promotes the expression of cytokinin signaling inhibitors, cytokinin signaling promotes the expression of auxin signaling inhibitors and finally where cytokinin signaling regulates the complex network of auxin transport proteins to position zones of high auxin signaling. We are witnessing a period of discovery in which we are beginning to understand how these hormonal pathways communicate to regulate root formation.

Research highlights▶ Auxin and cytokinin regulate diverse aspects of root development. ▶ Auxin and cytokinin signaling pathways merge to regulate the expression of key genes such as ARR7, ARR15 and SHY2. ▶ Cytokinin signaling affects the expression of the PIN proteins and thereby modulate auxin distribution.