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Abstract
The world is filled with flavors and scents, which are the result of volatile compounds produced and emitted by plants. These specialized metabolites 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 evolution, 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 acyltransferases, and the terpene syntheses. 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.
Key Words
specialized metabolism, volatile emission, repeated evolution, O-methyltransferases, acyltransferases, terpene syntheses
INTRODUCTION
We live in a world full of fragrances and flavors. Scents profoundly influence much of what humans and animals do. Many chemicals that are emitted by flowers, such as geranylacetate, phenylethanol, and methyleugenol, are pleasant to humans and to the insects such as bees and moths that use these molecules as cues to find food. Other compounds, such as cadaverine and putrescine, are repugnant to humans and are usually associated with the presence of rotting flesh. Flavors and scents are directly tied to food preference and palatability and to mate choice (41). A significant body of knowledge has grown to describe the flavor, scent, and aroma compounds produced by plants. Much of early organic chemistry research and significant efforts by the food and beverage industries have been directed toward understanding the nature of these properties of plants. The perfume and food industries know the importance of these compounds, and the artificial and natural flavor and fragrance business has been a multibillion dollar business for some time (89).
The purpose of this article is to review recent advancements in our understanding of the mechanisms responsible for the evolution of volatile compounds responsible for flavors and scents in higher plants. This review discusses the evolution of several gene families that are responsible for controlling production, in one way...