title: The Arabidopsis vitamin E pathway gene5-1 mutant reveals a critical role for phytol kinase in seed tocopherol biosynthesis.
abstract: We report the identification and characterization of a low tocopherol Arabidopsis thaliana mutant, vitamin E pathway gene5-1 (vte5-1), with seed tocopherol levels reduced to 20% of the wild type. Map-based identification of the responsible mutation identified a G-->A transition, resulting in the introduction of a stop codon in At5g04490, a previously unannotated gene, which we named VTE5. Complementation of the mutation with the wild-type transgene largely restored the wild-type tocopherol phenotype. A knockout mutation of the Synechocystis sp PCC 6803 VTE5 homolog slr1652 reduced Synechocystis tocopherol levels by 50% or more. Bioinformatic analysis of VTE5 and slr1652 indicated modest similarity to dolichol kinase. Analysis of extracts from Arabidopsis and Synechocystis mutants revealed increased accumulation of free phytol. Heterologous expression of these genes in Escherichia coli supplemented with free phytol and in vitro assays of recombinant protein produced phytylmonophosphate, suggesting that VTE5 and slr1652 encode phytol kinases. The phenotype of the vte5-1 mutant is consistent with the hypothesis that chlorophyll degradation-derived phytol serves as an important intermediate in seed tocopherol synthesis and forces reevaluation of the role of geranylgeranyl diphosphate reductase in tocopherol biosynthesis.
authors.affiliation: Monsanto Company, Chesterfield, Missouri 63017, USA.
authors.forename: Henry E
authors.initials: HE
authors.lastname: Valentin
authors.forename: Kim
authors.initials: K
authors.lastname: Lincoln
authors.forename: Farhad
authors.initials: F
authors.lastname: Moshiri
authors.forename: Pamela K
authors.initials: PK
authors.lastname: Jensen
authors.forename: Qungang
authors.initials: Q
authors.lastname: Qi
authors.forename: Tyamagondlu V
authors.initials: TV
authors.lastname: Venkatesh
authors.forename: Balasulojini
authors.initials: B
authors.lastname: Karunanandaa
authors.forename: Susan R
authors.initials: SR
authors.lastname: Baszis
authors.forename: Susan R
authors.initials: SR
authors.lastname: Norris
authors.forename: Beth
authors.initials: B
authors.lastname: Savidge
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Gruys
authors.forename: Robert L
authors.initials: RL
authors.lastname: Last
mesh_terms: D000595:Amino Acid Sequence; D000975:Antioxidants / Q000378:metabolism*; D017360:Arabidopsis / Q000033:anatomy & histology / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D019295:Computational Biology; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D009154:Mutation; D010770:Phosphotransferases / Q000145:classification / Q000235:genetics / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism; D010836:Phytol / Q000737:chemistry / Q000378:metabolism*; D030821:Plants, Genetically Modified; D012639:Seeds / Q000378:metabolism*; D016415:Sequence Alignment; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism; D019076:Transgenes; D014810:Vitamin E / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D029681:Arabidopsis Proteins; D014810:Vitamin E; D002734:Chlorophyll; D010836:Phytol; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); C020087:dolichol kinase