title: In planta functions of the Arabidopsis cytokinin receptor family.
abstract: Since their discovery as cell-division factors in plant tissue culture about five decades ago, cytokinins have been hypothesized to play a central role in the regulation of cell division and differentiation in plants. To test this hypothesis in planta, we isolated Arabidopsis plants lacking one, two, or three of the genes encoding a subfamily of histidine kinases (CRE1, AHK2, and AHK3) that function as cytokinin receptors. Seeds were obtained for homozygous plants containing mutations in all seven genotypes, namely single, double, and triple mutants, and the responses of germinated seedlings in various cytokinin assays were compared. Both redundant and specific functions for the three different cytokinin receptors were observed. Plants carrying mutations in all three genes did not show cytokinin responses, including inhibition of root elongation, inhibition of root formation, cell proliferation in and greening of calli, and induction of cytokinin primary-response genes. The triple mutants were small and infertile, with a reduction in meristem size and activity, yet they possessed basic organs: roots, stems, and leaves. These results confirm that cytokinins are a pivotal class of plant growth regulators but provide no evidence that cytokinins are required for the processes of gametogenesis and embryogenesis.
authors.affiliation: Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Higuchi
authors.forename: Melissa S
authors.initials: MS
authors.lastname: Pischke
authors.forename: Ari Pekka
authors.initials: AP
authors.lastname: Mähönen
authors.forename: Kaori
authors.initials: K
authors.lastname: Miyawaki
authors.forename: Yukari
authors.initials: Y
authors.lastname: Hashimoto
authors.forename: Motoaki
authors.initials: M
authors.lastname: Seki
authors.forename: Masatomo
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Kazuo
authors.initials: K
authors.lastname: Shinozaki
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Kato
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tabata
authors.forename: Ykä
authors.initials: Y
authors.lastname: Helariutta
authors.forename: Michael R
authors.initials: MR
authors.lastname: Sussman
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Kakimoto
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003583:Cytokinins / Q000378:metabolism*; D015870:Gene Expression; D017343:Genes, Plant; D000071677:Histidine Kinase; D005810:Multigene Family; D016254:Mutagenesis, Insertional; D010641:Phenotype; D018517:Plant Roots / Q000254:growth & development; D018520:Plant Shoots / Q000187:drug effects; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D003583:Cytokinins; D011956:Receptors, Cell Surface; D011494:Protein Kinases; D000071677:Histidine Kinase; C000605492:AHK2 protein, Arabidopsis; C000605493:AHK3 protein, Arabidopsis; C421783:WOL protein, Arabidopsis