Poster: Hormones

Abs # 568: Cyotokinin mediated His-to-Asp phosphorelay signal transduction in Arabidopsis thaliana, (II) Functional interaction between the AHK family of cytokinin receptors and type-B ARRs

Presenter:	Imamura, Aya , ayaima@agr.nagoya-u.ac.jp
Authors	Imamura, Aya  (A)   Tajima, Yoshinori  (A)   Mizuno, Takeshi  (A)
Affiliations:	(A): Graduate School of Bioaglicultural Sciences, Nagoya University,

In Arabidopsis thaliana, His-to-Asp phosphorelay is a paradigm of signaling systems that is considered to be involved in responses to plant hormones, including ethylene and cytokinin. In the current framework of His-Asp phosphorelays in this higher plant, the type-B response regulators (ARRs), consisting of 11 members, appear to act as DNA-binding transcriptional regulators at the downstream of certain histidine (His) kinases. Based on the phylogenetic analyses of the common receiver domains, these type-B ARR members can be classified into 3 groups. Except for some representatives (e.g., ARR1 and ARR2), nevertheless, no biological information is available with regard to other members. We here characterized another example of type-B ARR members, namely ARR11, which belongs to the same subgroup as ARR1/2. ARR11 was extensively characterized in terms of not only its in vitro biochemical properties, but also its biological activity in plants. In vitro, ARR11 showed the ability to acquire phosphoryl group from a histidine-containing phosphotransfer intermediate (AHP), and also it showed the ability to recognize a specific nucleotide sequence, GGATT. These in vitro results supported the view that ARR11 is indeed a DNA-binding transcription factor, the ability of which is most likely modulated by phosphorylation in its receiver domain. In vivo, when the C-terminal DNA-binding domain lacking the N-terminal phospho-accepting (or receiver) domain of those was aberrantly expressed, the resulting transgenic plants showed characteristic anomalies during development of apical parts. These results with regard to ARR11 will be discussed in the context of the cytokinin-mediated signal transduction in Arabidopsis thaliana.