Chlorophyta exclusively use the 1-deoxyxylulose 5-phosphate/2-C-methylerythritol 4-phosphate pathway for the biosynthesis of isoprenoids

The biosynthesis of the C-5 building block of isoprenoids, isopentenyl diph osphate (IPP), proceeds in higher plants via two basically different pathwa ys: in the cytosolic compartment sterols are formed via mevalonate (MVA), w hereas in the plastids the isoprenoids are formed via the 1-deoxyxylulose 5 -phosphate/2-C-methylerythritol 4-phosphate pathway (DOXP/MEP pathway). In the present investigation, we found for the Charophyceae, being close relat ives to land plants, and in the original green flagellate Mesostigma viride the same IPP biosynthesis pattern as in higher plants: sterols are formed via MVA, and the phytol-moiety of chlorophylls via the DOXP/MEP pathway. In contrast, representatives of four classes of the Chlorophyta (Chlorophycea e, Ulvophyceae, Trebouxiophyceae, Prasinophyceae) did not incorporate MVA i nto sterols or phytol. Instead, they incorporated [1-H-2(1)]-1-deoxy-D-xylu lose into phytol and sterols. The results indicate that the entire Chloroph yta lineage, which is well separated from the land plant/Charophyceae linea ge, is devoid of the acetate/MVA pathway and uses the DOXP/MEP pathway not only for plastidic, but also for cytosolic isoprenoid formation.