Five geranylgeranyl diphosphate synthases expressed in different organs are localized into three subcellular compartments in Arabidopsis

Geranylgeranyl diphosphate (GGPP) is the precursor for the biosynthesis of gibberellins, carotenoids, chlorophylls, isoprenoid quinones, and geranylge ranylated proteins in plants. There is a small gene family for GGPP synthas es encoding five isozymes and one related protein in Arabidopsis, and all h omologs have a putative localization signal to translocate into specific su bcellular compartments. Using a synthetic green fluorescent protein (sGFP), we studied the subcellular localization of these GGPP synthases. When thes e fusion proteins were expressed by the cauliflower mosaic virus 35S promot er in Arabidopsis, GGPS1-sGFP and GGPS3-sGFP proteins were translocated int o the chloroplast, GGPS2-sGFP and GGPS4-sGFP proteins were localized in the endoplasmic reticulum, and the GGPS6-sGFP protein was localized in the mit ochondria, Both GGPS1 and GGPS3 proteins synthesized in vitro were taken up into isolated intact pea chloroplasts and processed to the mature form. RN A-blot and promoter-beta-glucuronidase (GUS) analysis showed that these GGP P synthases genes are organ-specifically expressed in Arabidopsis. GGR and GGPS1 were ubiquitously expressed, while GGPS2, GGPS3, and GGPS4 were expre ssed specifically in the flower, root, and flower, respectively. These resu lts suggest that each GGPP synthase gene is expressed in different tissues during plant development and GGPP is synthesized by the organelles themselv es rather than being transported into the organelles. Therefore, we predict there will be specific pathways of GGPP production in each organelle.