Structural basis for cytokinin recognition by Arabidopsis thaliana histidine kinase 4

Abstract

Histidine kinase 4 from Arabidopsis thaliana (AHK4) is a membrane-bound receptor for cytokinins, a class of plant hormones involved in growth, development and defense. Crystal structures of the AHK4 sensor domain in complex with various natural and synthetic cytokinins reveal important features of ligand recognition by this cytokinin receptor. Cytokinins are classic hormones that orchestrate plant growth and development and the integrity of stem cell populations. Cytokinin receptors are eukaryotic sensor histidine kinases that are activated by both naturally occurring adenine-type cytokinins and urea-based synthetic compounds. Crystal structures of the Arabidopsis thaliana histidine kinase 4 sensor domain in complex with different cytokinin ligands now rationalize the hormone-binding specificity of the receptor and may spur the design of new cytokinin ligands.