DEVELOPMENTAL AND STRESS REGULATION OF GENE-EXPRESSION FOR PLASTID AND CYTOSOLIC ISOPRENOID PATHWAYS IN PEPPER FRUITS

Plant cells synthesize a myriad of isoprenoid compounds in different s ubcellular compartments, which include the plastid, the mitochondria, and the endoplasmic reticulum cytosol. To start the study of the regul ation of these parallel pathways, we used pepper (Capsicum annuum) fru it as a model. Using different isoprenoid biosynthetic gene probes fro m cloned cDNAs, we showed that only genes encoding the plastid enzymes (geranylgeranyl pyrophosphate synthase, phytoene synthase, phytoene d esaturase, and capasan-thin-capsorubin synthase) are specifically trig gered during the normal period of development, at the ripening stage. This pattern of expression can be mimicked and precociously induced by a simple wounding stress. Concerning the cytosol-located enzymes, we observed that the expression of the gene encoding farnesyl pyrophospha te synthase is constitutive, whereas that of farnesyl pyrophosphate cy clase (5-epi-aristolochene synthase) is undetectable during the normal development of the fruit. The expression of these later genes are, ho wever, only selectively triggered after elicitor treatment. The result s provide evidence for developmental control of isoprenoid biosynthesi s occurring in plastids and that cytoplasmic isoprenoid biosynthesis i s regulated, in part, by environmental signals.