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GENETICS, GENOMICS, AND MOLECULAR EVOLUTION

Unraveling the Evolution of Cytokinin Signaling^[C],[W],[OA]

Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, United Kingdom (B.P.); and Institute of Biology/Applied Genetics, Free University of Berlin, 14195 Berlin, Germany (A.H.)

The conquest of the land by plants required dramatic morphological and metabolic adaptations. Complex developmental programs under tight regulation evolved during this process. Key regulators of plant development are phytohormones, such as cytokinins. Cytokinins are adenine derivatives that affect various processes in plants. The cytokinin signal transduction system, which is mediated via a multistep variant of the bacterial two-component signaling system, is well characterized in the model plant Arabidopsis (Arabidopsis thaliana). To understand the origin and evolutionary pattern of this signaling pathway, we surveyed the genomes of several sequenced key plant species ranging from unicellular algae, moss, and lycophytes, to higher land plants, including Arabidopsis and rice (Oryza sativa), for proteins involved in cytokinin signal transduction. Phylogenetic analysis revealed that the hormone-binding receptor and a class of negative regulators first appeared in land plants. Other components of the signaling pathway were present in all species investigated. Furthermore, we found that the receptors evolved under different evolutionary constraints from the other components of the pathway: The number of receptors remained fairly constant, while the other protein families expanded.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Alexander Heyl (heyl{at}zedat.fu-berlin.de).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.139188

^* Corresponding author; e-mail heyl{at}zedat.fu-berlin.de.

Received April 2, 2009; accepted August 6, 2009; published August 12, 2009.

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