title: Characterization of an Arabidopsis mutant deficient in gamma-tocopherol methyltransferase.
abstract: Alpha-tocopherol (vitamin E) is synthesized from gamma-tocopherol in chloroplasts by gamma-tocopherol methyltransferase (gamma-TMT; VTE4). Leaves of many plant species including Arabidopsis contain high levels of alpha-tocopherol, but are low in gamma-tocopherol. To unravel the function of different forms of tocopherol in plants, an Arabidopsis plant (vte4-1) carrying a functional null mutation in the gene gamma-TMT was isolated by screening a mutant population via thin-layer chromatography. A second mutant allele (vte4-2) carrying a T-DNA insertion in the coding sequence of gamma-TMT was identified in a T-DNA tagged mutant population. In vte4-1 and vte4-2 leaves, high levels of gamma-tocopherol accumulated, whereas alpha-tocopherol was absent indicating that, presumably, these two mutants represents null alleles. Over-expression of the gamma-TMT cDNA in vte4-1 restored wild-type tocopherol composition. Mutant plants were very similar to wild type. During oxidative stress (high light, high temperature, cold treatment) the amounts of alpha-tocopherol and gamma-tocopherol increased in wild type, and gamma-tocopherol in vte4-1. However, chlorophyll content and photosynthetic quantum yield were very similar in wild type and vte4-1, suggesting that alpha-tocopherol can be replaced by gamma-tocopherol in vte4-1 to protect the photosynthetic apparatus against oxidative stress. Fatty acid and lipid composition were very similar in WT, vte4-1 and vte1, an Arabidopsis mutant previously isolated which is completely devoid of tocopherol. Therefore, a shift in tocopherol composition or the absence of tocopherol has no major impact on the amounts of specific fatty acids or on lipid hydrolysis.
authors.affiliation: Max Planck Institute of Molecular Plant Physiology, Department of Lothar Willmitzer, Am Mühlenberg 1, 14476 Golm, Germany.
authors.forename: Eveline
authors.initials: E
authors.lastname: Bergmüller
authors.forename: Svetlana
authors.initials: S
authors.lastname: Porfirova
authors.forename: Peter
authors.initials: P
authors.lastname: Dörmann
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D008780:Methyltransferases / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D010641:Phenotype; D024505:Tocopherols / Q000378:metabolism
chemical_list: D008780:Methyltransferases; C047259:gamma-tocopherol methyltransferase; D024505:Tocopherols