Arabidopsis thaliana contains two differentially expressed farnesyl-diphosphate synthase genes.

The enzyme farnesyl-diphosphate synthase (FPS; EC 2.5.1.1/EC 2.5.1.10) catalyzes the synthesis of farnesyl diphosphate (FPP) from isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). This reaction is considered to be a rate-limiting step in isoprenoid biosynthesis. Southern blot analysis indicates that Arabidopsis thaliana contains at least 2 genes (FPS1 and FPS2) encoding FPS. The FPS1 and FPS2 genes have been cloned and characterized. The two genes have a very similar organization with regard to intron positions and exon sizes and share a high level of sequence similarity, not only in the coding region but also in the intronic sequences. Northern blot analysis showed that FPS1 and FPS2 have a different pattern of expression. FPS1 mRNA accumulates preferentially in roots and inflorescences, whereas FPS2 mRNA is predominantly expressed in inflorescences. The cDNA corresponding to the FPS1 gene was isolated by functional complementation of a mutant yeast strain defective in FPS activity (Delourme, D., Lacroute, F., and Karst, F. (1994) Plant Mol. Biol. 26, 1867-1873). By using a reverse transcription-polymerase chain reaction strategy we have cloned the cDNA corresponding to the FPS2 gene. Analysis of the FPS2 cDNA sequence revealed an open reading frame encoding a protein of 342 amino acid residues with a predicted molecular mass of 39,825 Da. FPS1 and FPS2 isoforms share an overall amino acid identity of 90.6%. Arabidopsis FPS2 was able to rescue the lethal phenotype of an ERG20-disrupted yeast strain. We demonstrate that FPS2 catalyzes the two successive condensations of IPP with both DMAPP and geranyl diphosphate leading to FPP. The significance of the occurrence of different FPS isoforms in plants is discussed in the context of the complex organization of the plant isoprenoid pathway.

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