Functional analyses of LONELY GUY cytokinin-activating enzymes reveal the importance of the direct activation pathway in Arabidopsis

Plant Cell. 2009 Oct;21(10):3152-69. doi: 10.1105/tpc.109.068676. Epub 2009 Oct 16.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / drug effects
  • Arabidopsis / enzymology*
  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / classification
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism
  • Arabidopsis Proteins / physiology*
  • Cytokinins / metabolism*
  • DNA, Bacterial / genetics
  • DNA, Bacterial / physiology
  • Dexamethasone / pharmacology
  • Genetic Complementation Test
  • Glucosides / metabolism
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism*
  • Isopentenyladenosine / metabolism
  • Mutagenesis, Insertional
  • Phylogeny
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction / drug effects
  • Signal Transduction / genetics
  • Signal Transduction / physiology


  • Arabidopsis Proteins
  • Cytokinins
  • DNA, Bacterial
  • Glucosides
  • Recombinant Proteins
  • T-DNA
  • Green Fluorescent Proteins
  • N(6)-(delta(2)-isopentenyl)adenine
  • Isopentenyladenosine
  • Dexamethasone