Journal Article

<i>Arabidopsis</i> Response Regulator, ARR22, Ectopic Expression of Which Results in Phenotypes Similar to the <i>wol</i> Cytokinin-Receptor Mutant

Takatoshi Kiba, Koh Aoki, Hitoshi Sakakibara and Takeshi Mizuno

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 45, issue 8, pages 1063-1077
Published in print August 2004 | ISSN: 0032-0781
Published online August 2004 | e-ISSN: 1471-9053 | DOI:
Arabidopsis Response Regulator, ARR22, Ectopic Expression of Which Results in Phenotypes Similar to the wol Cytokinin-Receptor Mutant

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry


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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.

Keywords: Keywords: Arabidopsis — Cytokinin — Histidine kinase — Phosphorelay — Response regulator — Signal transduction.; Abbreviations: AHK, Arabidopsis histidine kinase; AHP, Arabidopsis histidine-containing phosphotransmitter; ARR, Arabidopsis response regulator.

Journal Article.  10250 words.  Illustrated.

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

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