title: Overexpression of Arabidopsis response regulators, ARR4/ATRR1/IBC7 and ARR8/ATRR3, alters cytokinin responses differentially in the shoot and in callus formation.
abstract: Arabidopsis ARR4/ATRR1/IBC7 and ARR8/ATRR3 are homologous genes of prokaryotic response regulators that are involved in the His-Asp phosphorelay signal transduction. We analyzed the function of these genes as response regulators using transgenic plants. Overexpression of ARR4 in cultured stems of the transgenics markedly promoted shoot formation in the presence of cytokinin, while overexpression of ARR8 repressed shoot formation and greening of calli. The expression level of cytokinin-inducible genes, cycD3 and cab increased in the ARR4 overexpressor but decreased in the ARR8 overexpressor. By contrast, two drought stress-inducible genes, rd29A and erd1, were expressed in both overexpressors as that in control plants. These results suggest that ARR4 and ARR8 are involved in cytokinin signal transduction, and that ARR4 functions as a positive-regulator, whereas ARR8 functions as a negative-regulator. Furthermore, microarray analysis showed that several genes were up-regulated in the ARR4 overexpressor. Consistent with these results, ARR4 and ARR8 might play important roles in the sensoring system of cytokinin signal transduction pathway in various developmental and environmental conditions and the regulation of gene expression.
authors.affiliation: Biological Resources Division, Japan International Research Center for Agricultural Sciences, 1-1 Ohwashi, Tsukuba, Ibaraki 305-8686, Japan.
authors.forename: Yuriko
authors.initials: Y
authors.lastname: Osakabe
authors.forename: Shinichi
authors.initials: S
authors.lastname: Miyata
authors.forename: Takeshi
authors.initials: T
authors.lastname: Urao
authors.forename: Motoaki
authors.initials: M
authors.lastname: Seki
authors.forename: Kazuo
authors.initials: K
authors.lastname: Shinozaki
authors.forename: Kazuko
authors.initials: K
authors.lastname: Yamaguchi-Shinozaki
mesh_terms: D017360:Arabidopsis / Q000033:anatomy & histology / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D003583:Cytokinins / Q000494:pharmacology*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D007700:Kinetics; D009928:Organ Specificity; D010802:Phylogeny; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development; D030821:Plants, Genetically Modified; D018749:RNA, Plant / Q000096:biosynthesis; D015398:Signal Transduction; D014158:Transcription, Genetic
chemical_list: C113359:ARR4 protein, Arabidopsis; C459457:ARR8 protein, Arabidopsis; D029681:Arabidopsis Proteins; D003583:Cytokinins; D018749:RNA, Plant