One of several potential approaches to study mechanisms of action of biologically active compounds is to develop their agonists and antagonists. In the present study, we report the identification of the first known molecule antagonizing the activity of the plant hormone cytokinin at the receptor level. This compound, 6-(2-hydroxy-3-methylbenzylamino)purine, designated PI-55 in the present study, is structurally closely related to cytokinin 6-benzylaminopurine, but substitutions at specific positions of the aromatic side chain strongly diminished its cytokinin activity and conferred antagonistic properties. PI-55 competitively inhibited the binding of the natural ligand trans-zeatin to the Arabidopsis cytokinin receptors cytokinin response 1 (CRE1)/Arabidopsis histidine kinase (AHK) 4 and AHK3 and repressed induction of the cytokinin response gene ARR5:GUS. Genetic analysis revealed that CRE1/AHK4 is the primary target of PI-55. Cytokinin bioassays also demonstrated the anticytokinin effect of PI-55 in several other species. Furthermore, we show that PI-55 accelerated the germination of Arabidopsis seeds and promoted the root growth and formation of lateral roots, thus phenocopying the known consequences of a lowered cytokinin status and demonstrating its potential to inhibit cytokinin perception in planta. PI-55 is the first example for the targeted development of a cytokinin antagonist and represents an initial step for the preparation of cytokinin antagonists with broad activity and reduced agonistic properties.

Laboratory of Growth Regulators Institute of Experimental Botany AS CR and Palacký University Olomouc Czech Republic

References provided by Crossref.org

Primary multistep phosphorelay activation comprises both cytokinin and abiotic stress responses: insights from comparative analysis of Brassica type-A response regulators

The Role of a Cytokinin Antagonist in the Progression of Clubroot Disease

Sucrose promotes stem branching through cytokinin

Naturally Occurring and Artificial N9-Cytokinin Conjugates: From Synthesis to Biological Activity and Back

Root ABA and H+-ATPase are key players in the root and shoot growth-promoting action of humic acids

A Stimulatory Role for Cytokinin in the Arbuscular Mycorrhizal Symbiosis of Pea

Haustorium initiation in the obligate parasitic plant Phelipanche ramosa involves a host-exudated cytokinin signal

Cytokinin-Auxin Crosstalk in the Gynoecial Primordium Ensures Correct Domain Patterning

Cytokinins Are Initial Targets of Light in the Control of Bud Outgrowth

N9-substituted aromatic cytokinins with negligible side effects on root development are an emerging tool for in vitro culturing

Novel cytokinin derivatives do not show negative effects on root growth and proliferation in submicromolar range