Cytokinin and Ethylene Signaling
Cytokinins and ethylene belong to the group of “classical” plant growth regulators controlling a broad spectrum of developmental responses. Models for cytokinin and ethylene signal transduction have been established mainly in Arabidopsis, but the signaling pathways of both phytohormones are believed to be conserved throughout the plant kingdom. Nonetheless, in spite of several decades of intense research, our knowledge on basic principles driving signal recognition and transduction of both phytohormones is still delimited. Cytokinins and ethylene are recognized by proteins from the same family of sensor histidine kinases. However, the mechanism of signal transduction through the (plasma) membrane as well as the downstream members of both signaling cascades differ for cytokinins and ethylene. While cytokinins activate multistep phosphorelay signaling of bacterial origin, ethylene signal is perceived by a series of negative regulations mediated by redundant ethylene sensors and downstream Raf-like kinase.
Here, we provide an up-to-date overview of known structures and function–structure relationships of main components of cytokinin and ethylene signaling in Arabidopsis. We demonstrate how the knowledge deepens our understanding of molecular principles underlying signal recognition and transduction via both hormonal pathways while raising new questions that remain to be answered. Finally, we summarize the recently published evidence, providing mechanistic insights into the long suspected cytokinin/ethylene signaling crosstalk.
This work was supported by the Czech Science Foundation, grant 13-25280S, and by the Ministry of Education, Youth and Sports of the Czech Republic under the project CEITEC 2020 (LQ1601) and CZ.02.1.01/0.0/0.0/16_026/0008446.
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