title: Myoinositol oxygenase controls the level of myoinositol in Arabidopsis, but does not increase ascorbic acid.
abstract: Ascorbic acid (AsA) is a major plant antioxidant. Mutants like vtc1 show a reduced AsA concentration, which confirmed by genetic evidence the previously proposed AsA pathway via GDP-Man. Here we investigate the role of an animal-like alternative biosynthesis route to AsA, starting from the metabolite D-GlcUA, which is produced in plants by myoinositol oxygenase (Miox). Miox-overexpressing lines have a more than 30-fold up-regulated transcript level and higher enzymatic activity as shown by increased incorporation of Miox-derived sugars into cell wall polymers. In addition, Miox overexpressors exhibit a lower steady-state level of myoinositol and accumulate less myoinositol in feeding experiments due to an enhanced turnover rate. The AsA concentration remains the same in wild-type and Miox overexpressor lines. Even challenging plants with stress, which increases AsA concentration 4-fold, reveals no difference in AsA biosynthesis between wild-type and Miox-overexpressing lines. We conclude that D-GlcUA derived from the Miox reaction plays a negligible role for AsA biosynthesis. However, Miox controls the metabolite level of myoinositol in plants.
authors.affiliation: University of Salzburg, 5020 Salzburg, Austria.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Endres
authors.forename: Raimund
authors.initials: R
authors.lastname: Tenhaken
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001205:Ascorbic Acid / Q000096:biosynthesis / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D017931:DNA Primers; D003624:Darkness; D007294:Inositol / Q000378:metabolism*; D050562:Inositol Oxygenase / Q000235:genetics* / Q000378:metabolism*; D008027:Light; D018515:Plant Leaves / Q000201:enzymology; D016133:Polymerase Chain Reaction; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D017931:DNA Primers; D007294:Inositol; D050562:Inositol Oxygenase; D001205:Ascorbic Acid