Disease relevance of AHK3

• 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 [1].

High impact information on AHK3

• Together, the analyses reveal partially redundant functions of the cytokinin receptors and prominent roles for the AHK2/AHK3 receptor combination in quantitative control of organ growth in plants, with opposite regulatory functions in roots and shoots [2].
• Application of exogenous cytokinins to the resultant strains revealed that both AHK2 and AHK3 function as positive regulators for cytokinin signaling similar to AHK4 [3].
• Cytokinin-mediated control of leaf longevity by AHK3 through phosphorylation of ARR2 in Arabidopsis [4].
• This result was obtained through identification of a gain-of-function Arabidopsis mutant that shows delayed leaf senescence because of a missense mutation in the extracellular domain of AHK3 [4].
• A loss-of-function mutation in AHK3, but not of the other cytokinin receptors, conferred a reduced sensitivity to cytokinin in cytokinin-dependent delay of leaf senescence and abolished cytokinin-dependent phosphorylation of ARR2 [4].

Biological context of AHK3

• To gain further insights into this aspect of cytokinin action, we characterized a mutant with reduced sensitivity to cytokinin repression of a Pi starvation-responsive reporter gene and show it corresponds to AHK3 [5].
• The ahk2 ahk4 and ahk3 ahk4 double mutants and the ahk single mutants grew normally, whereas the ahk2 ahk3 double mutants exhibited a semidwarf phenotype as to shoots, such as a reduced leaf size and a reduced influorescence stem length [3].

Associations of AHK3 with chemical compounds

• For AHK3, cytokinin ribosides (tZR, iPR) and cis-zeatin had true binding activity, although lower than that of tZ [6].
• AHK3 had an approximately 10-fold lower affinity to isopentenyladenine (iP) and its riboside, but a higher affinity to dihydrozeatin than CRE1/AHK4 [6].
• In contrast to their high activity in bioassays, the BAP derivatives were recognised with much lower sensitivity than trans-zeatin in both Arabidopsis thaliana AHK3 and AHK4 receptor assays [7].

Regulatory relationships of AHK3

• AHK3 suppresses a sensor histidine kinase mutant of yeast [8].

References