Isoprenoid biosynthesis: The evolution of two ancient and distinct pathways across genomes

Isopentenyl diphosphate (IPP) is the central intermediate in the biosynthes is of isoprenoids, the most ancient and diverse class of natural products. Two distinct routes of IPP biosynthesis occur in nature: the mevalonate pat hway and the recently discovered deoxyxylulose 5-phosphate (DXP) pathway. T he evolutionary history of the enzymes involved in both routes and the phyl ogenetic distribution of their genes across genomes suggest that the mevalo nate pathway is germane to archaebacteria, that the DXP pathway is germane to eubacteria, and that eukaryotes have inherited their genes for IPP biosy nthesis from prokaryotes. The occurrence of genes specific to the DXP pathw ay is restricted to plastid-bearing eukaryotes, indicating that these genes were acquired from the cyanobacterial ancestor of plastids, However, the i ndividual phylogenies of these genes, with only one exception, do not provi de evidence for a specific affinity between the plant genes and their cyano bacterial homologues. The results suggest that lateral gene transfer betwee n eubacteria subsequent to the origin of plastids has played a major role i n the evolution of this pathway.