Cloning, Characterization, and Heterologous Expression of cDNAs for Farnesyl Diphosphate Synthase from the Guayule Rubber Plant Reveals That This Prenyltransferase Occurs in Rubber Particles

Two farnesyl diphosphate synthase (FPS) cDNAʹs from a guayule stembark library were isolated and characterized. Both encodeMr39,000 proteins containing 432 amino acids that differ slightly in their deduced molecular weights and isoelectric points. They both contain the DDXXD motifs that are characteristic of prenyltransferases, and both isoforms show high homology to other plant FPS sequences but less overall homology to FPS sequences from nonplant sources. The two isoforms differ by 5% in their amino acid sequence. When expressed inEscherichia coli,each guayule isoform exhibits high specific activity that produces farnesyl diphosphate as the major isoprenoid and small amounts of geranyl diphosphate. Biochemical and immunological evidence also indicates that FPS is associated with guayule rubber particles. Antibodies to chicken FPS cross-react with both guayule isoforms expressed inE. coliand recognize a low abundanceMr39,000 protein in rubber particles purified from guayule stembark. Guayule FPS sequences show high homology to peptide fragments of the prenyltransferase associated with rubber particles fromHevea brasiliensis,suggesting that this enzyme may be important for rubber biosynthesis in both species.