Abstract
Phytol is a diterpene alcohol and a precursor for the biosynthesis of tocopherol, chlorophyll and phylloquinone. In plants, phytol is synthesized through the reduction of another diterpne, geranylgeraniol. A soluble chloroplast protein, geranylgeranyl reductase has been identified to catalyze the reduction of geranylgenraniol to form phytol. This protein is encoded by a nuclear gene, ChlP. We have previously shown that the suppression of ChlP expression results in the reduction of the tocopherol levels and in the occurrence of chlorophyll derivatives conjugated with a partially reduced geranylgeranyl side chain. In the course of screening for Arabidopsis mutants that were defective in chlorophyll metabolism, we isolated two mutant lines showing very similar phenotypes to those of the ChlP suppression line mentioned above. Therefore, we hypothesized that the activity of geranylgeranyl reductase was reduced in these mutants. We identified the mutations in a pair of homologous genes encoding chloroplast membrane proteins with unknown functions. These results indicate that chloroplast membrane-proteins other than geranylgeranyl reductase are involved in phytol biosynthesis.
