title: Arabidopsis response regulator, ARR22, ectopic expression of which results in phenotypes similar to the wol cytokinin-receptor mutant.
abstract: 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.
authors.affiliation: Laboratory of Molecular Microbiology, School of Agriculture, Nagoya University, Chikusa-ku, Nagoya, 464-8601 Japan.
authors.forename: Takatoshi
authors.initials: T
authors.lastname: Kiba
authors.forename: Koh
authors.initials: K
authors.lastname: Aoki
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sakakibara
authors.forename: Takeshi
authors.initials: T
authors.lastname: Mizuno
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001224:Aspartic Acid / Q000378:metabolism; D003583:Cytokinins / Q000378:metabolism / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000235:genetics; D006639:Histidine / Q000378:metabolism; D000071677:Histidine Kinase; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D019697:Onions / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation; D030821:Plants, Genetically Modified / Q000235:genetics*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D019076:Transgenes / Q000235:genetics*
chemical_list: C493632:ARR22 protein, Arabidopsis; D029681:Arabidopsis Proteins; D003583:Cytokinins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D001224:Aspartic Acid; D006639:Histidine; D011494:Protein Kinases; D000071677:Histidine Kinase