METABOLIC COMPARTMENTATION OF PLASTID PRENYLLIPID BIOSYNTHESIS - EVIDENCE FOR THE INVOLVEMENT OF A MULTIFUNCTIONAL GERANYLGERANYL REDUCTASE

The addition of phytyl side chain to chlorophylls, tocopherols and phy lloquinone is prerequisite to their integration into plastid membranes . We have cloned a cDNA encoding a pre-geranylgeranyl reductase from A rabidopsis thaliana. The deduced primary structure predicts a mature s ize with a molecular mass of 47 kDa and displays a characteristic dinu cleotide binding domain. Geranylgeranyl reductase expressed in Escheri chia coli sequentially catalyzes the reduction of geranylgeranyl-chlor ophyll a into phytyl-chlorophyll a as well as the reduction of free ge ranylgeranyl diphosphate into phytyl diphosphate. Due to its multifunc tionality and weak hydrophobicity, we suggest that in plastid the same geranylgeranyl reductase is recruited into the chlorophyll, the tocop herol and the phylloquinone pathways. The geranylgeranyl reductase gen e is up-regulated during etioplast to chloroplast and chloroplast deve lopment.