Conformational dynamics are a key factor in signaling mediated by the receiver domain of a sensor histidine kinase from .

Multistep phosphorelay (MSP) cascades mediate responses to a wide spectrum of stimuli, including plant hormonal signaling, but several aspects of MSP await elucidation. Here, we provide first insight into the key step of MSP-mediated phosphotransfer in a eukaryotic system, the phosphorylation of the receiver domain of the histidine kinase CYTOKININ-INDEPENDENT 1 (CKI1) from We observed that the crystal structures of free, Mg-bound, and beryllofluoridated CKI1 (a stable analogue of the labile phosphorylated form) were identical and similar to the active state of receiver domains of bacterial response regulators. However, the three CKI1 variants exhibited different conformational dynamics in solution.