Journal Article

Two Cytokinin Receptors of <i>Arabidopsis thaliana</i>, CRE1/AHK4 and AHK3, Differ in their Ligand Specificity in a Bacterial Assay

Lukáš Spíchal, Natalia Yu. Rakova, Michael Riefler, Takeshi Mizuno, Georgy A. Romanov, Miroslav Strnad and Thomas Schmülling

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 45, issue 9, pages 1299-1305
Published in print September 2004 | ISSN: 0032-0781
Published online September 2004 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pch132
Two Cytokinin Receptors of Arabidopsis thaliana, CRE1/AHK4 and AHK3, Differ in their Ligand Specificity in a Bacterial Assay

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Strains of Escherichia coli that express two different cytokinin receptors of Arabidopsis thaliana, CRE1/AHK4 and AHK3, were used to study the relative sensitivity of these receptors to various cytokinins. Both receptors were most sensitive to the bases of the isoprenoid-type cytokinins trans-zeatin and isopentenyladenine but differed significantly in the recognition of other cytokinin compounds. In particular, CRE1/AHK4 recognized at 1 µm concentration only trans-zeatin while AHK3 recognized cis-zeatin and dihydrozeatin as well, although with a lower sensitivity. Similarly, CRE1/AHK4 was not activated by cytokinin ribosides and ribotides, but AHK3 was. Comparisons using the ARR5::GUS fusion gene as a cytokinin reporter in Arabidopsis showed similar relative degrees of responses in planta, except that cytokinins with aromatic side chains showed much higher activities than in the bacterial assay. These results indicate that the diverse cytokinin compounds might have specific functions in the numerous cytokinin-regulated processes, which may depend in turn on different receptors and their associated signalling pathways. The importance of precise control of local concentrations of defined cytokinin metabolites to regulate the respective downstream event is corroborated.

Keywords: Keywords: Arabidopsis thaliana — Cytokinin — Cytokinin receptor — Plant hormone — Signal transduction.; Abbreviations: BA, N6-benzyladenine; cZ, cis-zeatin; DPU, diphenylurea; DZ, dihydrozeatin; DZR, dihydrozeatin riboside; iP, N6-(Δ2-isopentenyl)adenine; iPR, N6-(Δ2-isopentenyl)adenosine; K, kinetin; mT, meta-topolin; TDZ, thidiazuron; tZ, trans-zeatin; oT, ortho-topolin; tZR, trans-zeatin riboside; tZMP, trans-zeatin riboside 5′-monophosphate.

Journal Article.  4246 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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