Progress in plant metabolic engineering.

Abstract

Plants have been estimated to collectively synthesize more than 30,000 different terpenoids, of which many have useful applications in the manufacture of foods, industrial compounds, and pharmaceuticals. Terpenoids are synthesized from the condensation, in a head to tail fashion, of 5-carbon isoprene (or hemiterpene) units. Major terpenoid classes include mono-, sesqui-, and diterpenes, which are mostly secondary metabolites, as well as tri- and tetraterpenes, which are generally primary metabolites. This large family of compounds includes essential molecules such as carotenoids, gibberellins, abscissic acid and brassinosteroids, sterols, and the phytol chains of chlorophylls, tocopherols, and quinones. However, the vast majority are secondary metabolites, such as the volatile constituents of essential oils, and complex molecules like the anticancer drug paclitaxel that are thought to act as defensive agents (1).