title: CHASE domain-containing receptors play an essential role in the cytokinin response of the moss Physcomitrella patens.
abstract: While the molecular basis for cytokinin action is quite well understood in flowering plants, little is known about the cytokinin signal transduction in early diverging land plants. The genome of the bryophyte Physcomitrella patens (Hedw.) B.S. encodes three classical cytokinin receptors, the CHASE domain-containing histidine kinases, CHK1, CHK2, and CHK3. In a complementation assay with protoplasts of receptor-deficient Arabidopsis thaliana as well as in cytokinin binding assays, we found evidence that CHK1 and CHK2 receptors can function in cytokinin perception. Using gene targeting, we generated a collection of CHK knockout mutants comprising single (Δchk1, Δchk2, Δchk3), double (Δchk1,2, Δchk1,3, Δchk2,3), and triple (Δchk1,2,3) mutants. Mutants were characterized for their cytokinin response and differentiation capacities. While the wild type did not grow on high doses of cytokinin (1 µM benzyladenine), the Δchk1,2,3 mutant exhibited normal protonema growth. Bud induction assays showed that all three cytokinin receptors contribute to the triggering of budding, albeit to different extents. Furthermore, while the triple mutant showed no response in this bioassay, the remaining mutants displayed budding responses in a diverse manner to different types and concentrations of cytokinins. Determination of cytokinin levels in mutants showed no drastic changes for any of the cytokinins; thus, in contrast to Arabidopsis, revealing only small impacts of cytokinin signaling on homeostasis. In summary, our study provides a first insight into the molecular action of cytokinin in an early diverging land plant and demonstrates that CHK receptors play an essential role in bud induction and gametophore development.
authors.affiliation: Biozentrum Klein Flottbek, Universität Hamburg, Ohnhorststr. 18, D-22609 Hamburg, Germany klaus.von.schwartzenberg@uni-hamburg.de aheyl@adelphi.edu.
authors.forename: Klaus
authors.initials: K
authors.lastname: von Schwartzenberg
authors.affiliation: Biozentrum Klein Flottbek, Universität Hamburg, Ohnhorststr. 18, D-22609 Hamburg, Germany.
authors.forename: Ann-Cathrin
authors.initials: AC
authors.lastname: Lindner
authors.affiliation: Institute for Biology/ Applied Genetics, Dahlem Centre of Plant Sciences, Freie Universität Berlin, Albrecht-Thaer-Weg 6, D-14195 Berlin, Germany.
authors.forename: Njuscha
authors.initials: N
authors.lastname: Gruhn
authors.affiliation: Laboratory of Growth Regulators & Department of Chemical Biology and Genetics, Centre of the Region Haná for Biotechnological and Agricultural Research, Palacký University & Institute of Experimental Botany ASCR, Šlechtitelů 27, CZ-783 71 Olomouc, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Šimura
authors.affiliation: Laboratory of Growth Regulators & Department of Chemical Biology and Genetics, Centre of the Region Haná for Biotechnological and Agricultural Research, Palacký University & Institute of Experimental Botany ASCR, Šlechtitelů 27, CZ-783 71 Olomouc, Czech Republic.
authors.forename: Ondřej
authors.initials: O
authors.lastname: Novák
authors.affiliation: Laboratory of Growth Regulators & Department of Chemical Biology and Genetics, Centre of the Region Haná for Biotechnological and Agricultural Research, Palacký University & Institute of Experimental Botany ASCR, Šlechtitelů 27, CZ-783 71 Olomouc, Czech Republic.
authors.forename: Miroslav
authors.initials: M
authors.lastname: Strnad
authors.affiliation: Institut Jean-Pierre Bourgin, UMR1318 INRA-AgroParisTech, INRA Centre de Versailles-Grignon, Route de St-Cyr, 78026 Versailles Cedex, France.
authors.forename: Martine
authors.initials: M
authors.lastname: Gonneau
authors.affiliation: Institut Jean-Pierre Bourgin, UMR1318 INRA-AgroParisTech, INRA Centre de Versailles-Grignon, Route de St-Cyr, 78026 Versailles Cedex, France.
authors.forename: Fabien
authors.initials: F
authors.lastname: Nogué
authors.affiliation: Institute for Biology/ Applied Genetics, Dahlem Centre of Plant Sciences, Freie Universität Berlin, Albrecht-Thaer-Weg 6, D-14195 Berlin, Germany Biology Department, Adelphi University, Science 116, 1 South Avenue, PO Box 701, Garden City, NY 11530-070, USA klaus.von.schwartzenberg@uni-hamburg.de aheyl@adelphi.edu.
authors.forename: Alexander
authors.initials: A
authors.lastname: Heyl
mesh_terms: D000222:Adaptation, Physiological; D001681:Biological Assay; D019068:Bryopsida / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D002070:Butadienes / Q000494:pharmacology; D003583:Cytokinins / Q000494:pharmacology*; D018506:Gene Expression Regulation, Plant; D055786:Gene Knockout Techniques; D045782:Hemiterpenes / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D010420:Pentanes / Q000494:pharmacology; D010641:Phenotype; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D002070:Butadienes; D003583:Cytokinins; D045782:Hemiterpenes; D010420:Pentanes; D010940:Plant Proteins; D011956:Receptors, Cell Surface; C005059:isoprene
keywords: Bryophyte; Physcomitrella patens; cytokinin; cytokinin receptor; evolution; moss; phytohormone; plant growth regulator; signaling; two-component system.