title: Functional analyses of LONELY GUY cytokinin-activating enzymes reveal the importance of the direct activation pathway in Arabidopsis.
abstract: Cytokinins play crucial roles in diverse aspects of plant growth and development. Spatiotemporal distribution of bioactive cytokinins is finely regulated by metabolic enzymes. LONELY GUY (LOG) was previously identified as a cytokinin-activating enzyme that works in the direct activation pathway in rice (Oryza sativa) shoot meristems. In this work, nine Arabidopsis thaliana LOG genes (At LOG1 to LOG9) were predicted as homologs of rice LOG. Seven At LOGs, which are localized in the cytosol and nuclei, had enzymatic activities equivalent to that of rice LOG. Conditional overexpression of At LOGs in transgenic Arabidopsis reduced the content of N(6)-(Delta(2)-isopentenyl)adenine (iP) riboside 5'-phosphates and increased the levels of iP and the glucosides. Multiple mutants of At LOGs showed a lower sensitivity to iP riboside in terms of lateral root formation and altered root and shoot morphology. Analyses of At LOG promoter:beta-glucuronidase fusion genes revealed differential expression of LOGs in various tissues during plant development. Ectopic overexpression showed pleiotropic phenotypes, such as promotion of cell division in embryos and leaf vascular tissues, reduced apical dominance, and a delay of leaf senescence. Our results strongly suggest that the direct activation pathway via LOGs plays a pivotal role in regulating cytokinin activity during normal growth and development in Arabidopsis.
authors.affiliation: RIKEN Plant Science Center, Tsurumi, Yokohama 230-0045, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kuroha
authors.forename: Hiroki
authors.initials: H
authors.lastname: Tokunaga
authors.forename: Mikiko
authors.initials: M
authors.lastname: Kojima
authors.forename: Nanae
authors.initials: N
authors.lastname: Ueda
authors.forename: Takashi
authors.initials: T
authors.lastname: Ishida
authors.forename: Shingo
authors.initials: S
authors.lastname: Nagawa
authors.forename: Hiroo
authors.initials: H
authors.lastname: Fukuda
authors.forename: Keiko
authors.initials: K
authors.lastname: Sugimoto
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sakakibara
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D003583:Cytokinins / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics / Q000502:physiology; D003907:Dexamethasone / Q000494:pharmacology; D005816:Genetic Complementation Test; D005960:Glucosides / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism*; D007541:Isopentenyladenosine / Q000378:metabolism; D016254:Mutagenesis, Insertional; D010802:Phylogeny; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D003583:Cytokinins; D004269:DNA, Bacterial; D005960:Glucosides; D011994:Recombinant Proteins; C036483:T-DNA; D049452:Green Fluorescent Proteins; C001478:N(6)-(delta(2)-isopentenyl)adenine; D007541:Isopentenyladenosine; D003907:Dexamethasone