title: The type-A response regulator, ARR15, acts as a negative regulator in the cytokinin-mediated signal transduction in Arabidopsis thaliana.
abstract: The Arabidopsis thaliana AHK4 histidine kinase (also known as CRE1 or WOL) acts as a cytokinin signal transducer, presumably, in concert with downstream components, such as histidine-containing phosphotransfer factors (AHPs) and response regulators (ARRs), through the histidine-to-aspartate (His-->Asp) phosphorelay. Among 10 members of the type-A ARR family, the cytokinin-induced expression of ARR15 in roots is selectively impaired in the cre1-1 mutant, which carries a mutation in the AHK4 gene, suggesting a link between this type-A response regulator and the AHK4-mediated cytokinin signal transduction in roots. To address this issue further, we characterized a T-DNA insertion mutant of ARR15, and also constructed transgenic lines (referred to as ARR15-ox) that overexpress the ARR15 gene in a manner independent of cytokinin. While the T-DNA insertion mutant (arr15-1) showed no apparent phenotype, the cytokinin-independent overexpression of ARR15 in ARR15-ox plants resulted in a reduced sensitivity toward exogenously applied cytokinin, not only in elongation of roots in plants, but also in green callus formation (or shoot formation) in explants. Cytokinin-induced expressions of certain type-A ARRs were also down-regulated in ARR15-ox plants. These results support the view that ARR15 acts as a repressor that mediates a negative feedback loop in the cytokinin and AHK4-mediated His-->Asp phosphorelay.
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: Hisami
authors.initials: H
authors.lastname: Yamada
authors.forename: Shusei
authors.initials: S
authors.lastname: Sato
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Kato
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tabata
authors.forename: Takafumi
authors.initials: T
authors.lastname: Yamashino
authors.forename: Takeshi
authors.initials: T
authors.lastname: Mizuno
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology*; D003583:Cytokinins / Q000378:metabolism*; D004269:DNA, Bacterial; D016254:Mutagenesis, Insertional; D030821:Plants, Genetically Modified; D015398:Signal Transduction
chemical_list: C470377:ARR15 protein, Arabidopsis; D029681:Arabidopsis Proteins; D003583:Cytokinins; D004269:DNA, Bacterial; C036483:T-DNA