EVOLUTION OF FLAVORS AND SCENTS

The world is filled with flavors and scents, which are the result of volatile compounds produced and emitted by plants. These specialized metabolitesA metabolite, usually a small molecule, which is not a building block of proteins, lipids, or sugars, but that plays another role in the organism. Usually, but not always, its occurrence is restricted. are the products of specific metabolic pathways. The terpenoid, fatty acid, and phenylpropanoid pathways contribute greatly to production of volatile compounds. Mechanisms that lead to evolution of volatile production in plants include gene duplication and divergence, convergent evolution, repeated evolutionThis occurs when a new and identical (or very similar) genetic function arises independently in the same gene family from two or more orthologous or paralogous genes that did not share the same function. , and alteration of gene expression, caused by a number of factors, followed by change in enzyme specificity. Many examples of these processes are now available for three important gene families involved in production of volatile metabolites: the small molecule O-methyltransferases, the acyltransferasesAn enzyme that catalyzes the formation of esters and amides via transfer from the co-enzyme A derivate of acid moieties to a receptive alcohol. , and the terpene synthasesA member of the large family of enzymes that catalyze the formation of terpenoid (isoprenoid) specialized metabolites from geranyl diphosphate, farnesyl diphosphate, or geranylgeranyl diphosphate via a carbocation intermediate. . Examples of these processes in these gene families are found in roses, Clarkia breweri, and sweet basil, among others. Finally, evolution of volatile emission will be an exciting field of study for the foreseeable future.