title: Characterization of genes involved in cytokinin signaling and metabolism from rice.
abstract: Two-component signaling elements play important roles in plants, including a central role in cytokinin signaling. We characterized two-component elements from the monocot rice (Oryza sativa) using several complementary approaches. Phylogenetic analysis reveals relatively simple orthologous relationships among the histidine kinases in rice and Arabidopsis (Arabidopsis thaliana). In contrast, the histidine-containing phosphotransfer proteins (OsHPs) and response regulators (OsRRs) display a higher degree of lineage-specific expansion. The intracellular localizations of several OsHPs and OsRRs were examined in rice and generally found to correspond to the localizations of their dicot counterparts. The functionality of rice type-B OsRRs was tested in Arabidopsis; one from a clade composed of both monocot and dicot type-B OsRRs complemented an Arabidopsis type-B response regulator mutant, but a type-B OsRR from a monocot-specific subfamily generally did not. The expression of genes encoding two-component elements and proteins involved in cytokinin biosynthesis and degradation was analyzed in rice roots and shoots and in response to phytohormones. Nearly all type-A OsRRs and OsHK4 were up-regulated in response to cytokinin, but other cytokinin signaling elements were not appreciably affected. Furthermore, multiple cytokinin oxidase (OsCKX) genes were up-regulated by cytokinin. Abscisic acid treatment decreased the expression of several genes involved in cytokinin biosynthesis and degradation. Auxin affected the expression of a few genes; brassinosteroid and gibberellin had only modest effects. Our results support a shared role for two-component elements in mediating cytokinin signaling in monocots and dicots and reveal how phytohormones can impact cytokinin function through modulating gene expression.
authors.affiliation: Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
authors.forename: Yu-Chang
authors.initials: YC
authors.lastname: Tsai
authors.forename: Nicholas R
authors.initials: NR
authors.lastname: Weir
authors.forename: Kristine
authors.initials: K
authors.lastname: Hill
authors.forename: Wenjing
authors.initials: W
authors.lastname: Zhang
authors.forename: Hyo Jung
authors.initials: HJ
authors.lastname: Kim
authors.forename: Shin-Han
authors.initials: SH
authors.lastname: Shiu
authors.forename: G Eric
authors.initials: GE
authors.lastname: Schaller
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Kieber
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics; D003583:Cytokinins / Q000235:genetics* / Q000378:metabolism / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics*; D005816:Genetic Complementation Test; D007210:Indoleacetic Acids / Q000494:pharmacology; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D012275:Oryza / Q000187:drug effects / Q000235:genetics*; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics; D018520:Plant Shoots / Q000187:drug effects / Q000235:genetics; D021381:Protein Transport / Q000187:drug effects; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D015203:Reproducibility of Results; D016415:Sequence Alignment; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics*; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism
chemical_list: D003583:Cytokinins; D007210:Indoleacetic Acids; D010940:Plant Proteins