Plant Cell Advance Online Publication Published on December 16, 2005; 10.1105/tpc.105.037077
OPEN ACCESS ARTICLE
Received August 24, 2005
Returned for revision October 3, 2005
Accepted November 14, 2005
The Arabidopsis vitamin E pathway gene5-1 Mutant Reveals a Critical Role for Phytol Kinase in Seed Tocopherol Biosynthesis
Henry E. Valentin 1*, Kim Lincoln 2, Farhad Moshiri 1, Pamela K. Jensen 3, Qungang Qi 1, Tyamagondlu V. Venkatesh 3, Balasulojini Karunanandaa 3, Susan R. Baszis 1, Susan R. Norris 2, Beth Savidge 4, Kenneth J. Gruys 1, and Robert L. Last 2
1 Monsanto Company, Chesterfield, Missouri 63017
2 Cereon Genomics, Cambridge, Massachusetts 02492
3 Monsanto Company, St. Louis, Missouri 63167
4 Monsanto Company, Calgene Campus, Davis, California 95616
* To whom correspondence should be addressed. E-mail: henry.e.valentin{at}monsanto.com.
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.
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