Arabidopsis response regulator, ARR22, ectopic expression of which results in phenotypes similar to the wol cytokinin-receptor mutant

Plant Cell Physiol. 2004 Aug;45(8):1063-77. doi: 10.1093/pcp/pch128.


Arabidopsis thaliana has a number of response regulators (ARRs) implicated in the histidine (His)-->aspartate (Asp) phosphorelay signal transduction. According to the current consistent model, both the type-A and type-B ARR family members play crucial roles in the cytokinin signaling circuitry. However, this higher plant has a few extra ARRs, on which no attention has been paid so far. Characterization of these extra ARRs might provide us with new insight into the His-->Asp phosphorelay signal transduction in plants. For this reason, in this study we extensively examined the natures of such a representative (named ARR22). Transcripts of ARR22 were expressed predominantly in reproductive organs, and a GFP::ARR22 fusion protein was localized in the cytoplasmic space in onion epidermal cells. The purified ARR22 protein had the ability to undergo phosphorylation in vitro, when incubated with phospho-AHP5, indicating that ARR22 has the fundamental ability to participate into a His-Asp phosphorelay pathway in its own right. In plants, transgenic lines overexpressing ARR22 were characterized (referred to as ARR22-ox), which showed the characteristic dwarf phenotypes with poorly developed root systems. The results of Northern blot hybridization with selected sets of hormone-responsive genes suggested that cytokinin responses are selectively attenuated in ARR22-ox, while other hormone responses (auxin, ABA and ethylene) occur normally. The results of microarray analyses with cytokinin-treated wild-type and ARR22-ox plants further supported the view that cytokinin responses are globally attenuated in ARR22-ox, at least, at the level of gene regulation. Finally, we demonstrated that the dwarf phenotypes of ARR22-ox are very similar to those of the wooden leg (wol) mutant, which has a severe lesion in the AHK4/CRE1 cytokinin-receptor of histidine protein kinase. These results suggested that ARR22 might also be implicated, directly or indirectly, in the cytokinin-responsive His-->Asp phophorelay signal transduction.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / isolation & purification
  • Arabidopsis Proteins / metabolism*
  • Aspartic Acid / metabolism
  • Cytokinins / metabolism
  • Cytokinins / pharmacology
  • Gene Expression Regulation, Plant / drug effects
  • Gene Expression Regulation, Plant / genetics
  • Histidine / metabolism
  • Histidine Kinase
  • Molecular Sequence Data
  • Mutation / genetics*
  • Onions / genetics
  • Onions / metabolism
  • Phenotype
  • Phosphorylation
  • Plants, Genetically Modified / genetics*
  • Protein Kinases / genetics
  • Protein Kinases / metabolism
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Sequence Homology, Amino Acid
  • Signal Transduction / drug effects
  • Signal Transduction / genetics
  • Transcription Factors / genetics
  • Transcription Factors / isolation & purification
  • Transcription Factors / metabolism
  • Transgenes / genetics*


  • ARR22 protein, Arabidopsis
  • Arabidopsis Proteins
  • Cytokinins
  • Recombinant Fusion Proteins
  • Transcription Factors
  • Aspartic Acid
  • Histidine
  • Protein Kinases
  • Histidine Kinase