The 1-deoxy-d-xylulose-5-phosphate Pathway for Biosynthesis of Carotenoids and Other Plastidic Isoprenoids

Abstract

The biosynthesis of plastidic isoprenoids (carotenoids, phytol, plastoquinone-9) as well as cytosolic sterols and various terpenes seemed to have been established since around 1958 (see Review 1). From 14C-labeling studies it had been accepted that the photosynthetic plants and algae form their isoprenic C5-unit isopentenyl diphosphate (IPP) - as in animal systems and fungi - via the acetate/mevalonate (MVA) pathway (1, 2). Various observations on plastid isoprenoids were, however, not in agreement with this view. Thus, photosynthetically fixed 14CO2 was readily incorporated into plastidic isoprenoids (carotenoids, phytol, plastoquinone-9), whereas 14C-labeled acetate and MVA were rapidly incorporated into the cytosolic sterols, but only at low rates into the plastidic isoprenoids (see 1). In addition, mevinolin, a highly specific inhibitor of the HMG-CoA reductase, efficiently inhibited sterol accumulation, but did not affect the formation of carotenoids, phytol and plastoquinone-9 (3). After the detection of a novel IPP pathway in bacteria (4) we started in 1993 a re-investigation of the biosynthesis of plastidic isoprenoids in cooperation with the chemists M. Rohmer (Strasbourg) and F. W. Lichtenthaler (Darmstadt). Applying 13C- and 2H-labeling techniques, NMR spectroscopy and GC-MS analysis it was shown that green algae (chlorophyta), higher plants, and several other algae groups synthesize their plastidic isoprenoids including isoprene via the novel non-mevalonate 1-deoxy-d-xylulose-5-phosphate (DOXP) pathway (1, 5–12). This novel DOXP pathway of IPP formation, which is obviously located in plastids, is reviewed here.