title: Molecular characterization of cytokinin-responsive histidine kinases in maize. Differential ligand preferences and response to cis-zeatin.
abstract: Genes for cytokinin-responsive His-protein kinases (ZmHK1, ZmHK2, and ZmHK3a) were isolated from maize (Zea mays). Heterologous expression of each of the ZmHKs in Escherichia coli having the DeltarcsC and cpslacZ genetic background conferred cytokinin-inducibility of lacZ expression on the bacteria. In the recombinant E. coli system, ZmHK1 and ZmHK3a were more sensitive to free-base cytokinins than to the corresponding nucleosides; isopentenyladenine was most effective for ZmHK1, while ZmHK2 tended to be most sensitive to trans-zeatin and the riboside. In contrast to a known cytokinin receptor of Arabidopsis (AHK4/CRE1/WOL), all ZmHKs responded to cis-zeatin (cZ), which generally is believed to be inactive or only weakly active. In cultured maize cells, expression of ZmRR1, a cytokinin-inducible response regulator, was induced by cZ as well as by trans-zeatin. These results strongly suggest that maize cytokinin receptors differ in ligand preference, and that cZ is an active cytokinin at least in maize.
authors.affiliation: Plant Science Center, RIKEN, 1-7-22, Suehiro, Tsurumi, Yokohama 230-0045, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Yonekura-Sakakibara
authors.forename: Mikiko
authors.initials: M
authors.lastname: Kojima
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Yamaya
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sakakibara
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D003583:Cytokinins / Q000494:pharmacology*; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D000071677:Histidine Kinase; D008969:Molecular Sequence Data; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000494:pharmacology*; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D003313:Zea mays / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D015026:Zeatin / Q000494:pharmacology*
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D003583:Cytokinins; D018076:DNA, Complementary; D010937:Plant Growth Regulators; D010940:Plant Proteins; D015026:Zeatin; D011494:Protein Kinases; D000071677:Histidine Kinase