title: Cytokinin Regulates the Etioplast-Chloroplast Transition through the Two-Component Signaling System and Activation of Chloroplast-Related Genes.
abstract: One of the classical functions of the plant hormone cytokinin is the regulation of plastid development, but the underlying molecular mechanisms remain elusive. In this study, we employed a genetic approach to evaluate the role of cytokinin and its signaling pathway in the light-induced development of chloroplasts from etioplasts in Arabidopsis (Arabidopsis thaliana). Cytokinin increases the rate of greening and stimulates ultrastructural changes characteristic for the etioplast-to-chloroplast transition. The steady-state levels of metabolites of the tetrapyrrole biosynthesis pathway leading to the production of chlorophyll are enhanced by cytokinin. This effect of cytokinin on metabolite levels arises due to the modulation of expression for chlorophyll biosynthesis genes such as HEMA1, GUN4, GUN5, and CHLM Increased expression of HEMA1 is reflected in an enhanced level of the encoded glutamyl-tRNA reductase, which catalyzes one of the rate-limiting steps of chlorophyll biosynthesis. Mutant analysis indicates that the cytokinin receptors ARABIDOPSIS HIS KINASE2 (AHK2) and AHK3 play a central role in this process. Furthermore, the B-type ARABIDOPSIS RESPONSE REGULATOR1 (ARR1), ARR10, and ARR12 play an important role in mediating the transcriptional output during etioplast-chloroplast transition. B-type ARRs bind to the promotors of HEMA1 and LHCB6 genes, indicating that cytokinin-dependent transcription factors directly regulate genes of chlorophyll biosynthesis and the light harvesting complex. Together, these results demonstrate an important role for the cytokinin signaling pathway in chloroplast development, with the direct transcriptional regulation of chlorophyll biosynthesis genes as a key aspect for this hormonal control.
authors.affiliation: Institute of Biology/Applied Genetics, Dahlem Centre of Plant Sciences (DCPS), Freie Universität Berlin, Albrecht-Thaer-Weg 6, D-14195 Berlin, Germany (A.C., I.M., T.S.);Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755 (M.V.Y., K.H., G.E.S.); andDepartment of Plant Physiology, Humboldt Universität, Philippstrasse 13, D-10115 Berlin, Germany (H.S., B.G.).
authors.forename: Anne
authors.initials: A
authors.lastname: Cortleven
authors.affiliation: Institute of Biology/Applied Genetics, Dahlem Centre of Plant Sciences (DCPS), Freie Universität Berlin, Albrecht-Thaer-Weg 6, D-14195 Berlin, Germany (A.C., I.M., T.S.);Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755 (M.V.Y., K.H., G.E.S.); andDepartment of Plant Physiology, Humboldt Universität, Philippstrasse 13, D-10115 Berlin, Germany (H.S., B.G.).
authors.forename: Ingke
authors.initials: I
authors.lastname: Marg
authors.affiliation: Institute of Biology/Applied Genetics, Dahlem Centre of Plant Sciences (DCPS), Freie Universität Berlin, Albrecht-Thaer-Weg 6, D-14195 Berlin, Germany (A.C., I.M., T.S.);Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755 (M.V.Y., K.H., G.E.S.); andDepartment of Plant Physiology, Humboldt Universität, Philippstrasse 13, D-10115 Berlin, Germany (H.S., B.G.).
authors.forename: Maria V
authors.identifier: 0000-0001-6208-4228
authors.initials: MV
authors.lastname: Yamburenko
authors.affiliation: Institute of Biology/Applied Genetics, Dahlem Centre of Plant Sciences (DCPS), Freie Universität Berlin, Albrecht-Thaer-Weg 6, D-14195 Berlin, Germany (A.C., I.M., T.S.);Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755 (M.V.Y., K.H., G.E.S.); andDepartment of Plant Physiology, Humboldt Universität, Philippstrasse 13, D-10115 Berlin, Germany (H.S., B.G.).
authors.forename: Hagen
authors.initials: H
authors.lastname: Schlicke
authors.affiliation: Institute of Biology/Applied Genetics, Dahlem Centre of Plant Sciences (DCPS), Freie Universität Berlin, Albrecht-Thaer-Weg 6, D-14195 Berlin, Germany (A.C., I.M., T.S.);Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755 (M.V.Y., K.H., G.E.S.); andDepartment of Plant Physiology, Humboldt Universität, Philippstrasse 13, D-10115 Berlin, Germany (H.S., B.G.).
authors.forename: Kristine
authors.initials: K
authors.lastname: Hill
authors.affiliation: Institute of Biology/Applied Genetics, Dahlem Centre of Plant Sciences (DCPS), Freie Universität Berlin, Albrecht-Thaer-Weg 6, D-14195 Berlin, Germany (A.C., I.M., T.S.);Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755 (M.V.Y., K.H., G.E.S.); andDepartment of Plant Physiology, Humboldt Universität, Philippstrasse 13, D-10115 Berlin, Germany (H.S., B.G.).
authors.forename: Bernhard
authors.identifier: 0000-0002-9730-1074
authors.initials: B
authors.lastname: Grimm
authors.affiliation: Institute of Biology/Applied Genetics, Dahlem Centre of Plant Sciences (DCPS), Freie Universität Berlin, Albrecht-Thaer-Weg 6, D-14195 Berlin, Germany (A.C., I.M., T.S.);Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755 (M.V.Y., K.H., G.E.S.); andDepartment of Plant Physiology, Humboldt Universität, Philippstrasse 13, D-10115 Berlin, Germany (H.S., B.G.).
authors.forename: G Eric
authors.identifier: 0000-0003-4032-2437
authors.initials: GE
authors.lastname: Schaller
authors.affiliation: Institute of Biology/Applied Genetics, Dahlem Centre of Plant Sciences (DCPS), Freie Universität Berlin, Albrecht-Thaer-Weg 6, D-14195 Berlin, Germany (A.C., I.M., T.S.);Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755 (M.V.Y., K.H., G.E.S.); andDepartment of Plant Physiology, Humboldt Universität, Philippstrasse 13, D-10115 Berlin, Germany (H.S., B.G.) thomas.schmuelling@fu-berlin.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Schmülling
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001593:Benzyl Compounds / Q000494:pharmacology; D002736:Chloroplasts / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D003583:Cytokinins / Q000494:pharmacology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D061125:Genes, Chloroplast / Q000235:genetics*; D015151:Immunoblotting; D008027:Light; D046529:Microscopy, Electron, Transmission; D009154:Mutation; D010937:Plant Growth Regulators / Q000494:pharmacology; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D011687:Purines / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects
chemical_list: D029681:Arabidopsis Proteins; D001593:Benzyl Compounds; D003583:Cytokinins; D010937:Plant Growth Regulators; D011687:Purines; C480551:benzylaminopurine