myo-inositol oxygenase offers a possible entry point into plant ascorbate biosynthesis

Plant Physiol. 2004 Mar;134(3):1200-5. doi: 10.1104/pp.103.033936. Epub 2004 Feb 19.


Two biosynthetic pathways for ascorbate (l-ascorbic acid [AsA]; vitamin C) in plants are presently known, the mannose/l-galactose pathway and an l-GalUA pathway. Here, we present molecular and biochemical evidence for a possible biosynthetic route using myo-inositol (MI) as the initial substrate. A MI oxygenase (MIOX) gene was identified in chromosome 4 (miox4) of Arabidopsis ecotype Columbia, and its enzymatic activity was confirmed in bacterially expressed recombinant protein. Miox4 was primarily expressed in flowers and leaves of wild-type Arabidopsis plants, tissues with a high concentration of AsA. Ascorbate levels increased 2- to 3-fold in homozygous Arabidopsis lines overexpressing the miox4 open reading frame, thus suggesting the role of MI in AsA biosynthesis and the potential for using this gene for the agronomic and nutritional enhancement of crops.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Ascorbic Acid / biosynthesis*
  • Base Sequence
  • Cloning, Molecular
  • DNA, Plant / genetics
  • Escherichia coli / genetics
  • Flowers / metabolism
  • Gene Expression
  • Genes, Plant
  • Inositol Oxygenase
  • Models, Biological
  • Open Reading Frames
  • Oxygenases / genetics
  • Oxygenases / metabolism*
  • Plant Leaves / metabolism
  • Plants, Genetically Modified
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Tissue Distribution


  • DNA, Plant
  • Recombinant Proteins
  • Oxygenases
  • Inositol Oxygenase
  • Ascorbic Acid