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The monoterpene alcohol, linalool, is present in the floral fragrance of diverse plant families and is attractive to a broad spectrum of pollinators, herbivores and parasitoids. Floral emission of linalool has evolved de novo in the fragrant, moth-pollinated annual Clarkia breweri through a combination of up-regulation and ectopic expression of its biosynthetic enzyme, linalool synthase (LIS), in conjunction with allometric size increases in all floral organs. LIS activity and linalool emissions are 1000-fold lower in a sibling species, C. concinna, that is diurnally pollinated. LIS expression is spatially and temporally regulated during C. breweri flower development, immediately precedes free linalool emission and is absent from non-floral tissues. Its activity is highest in the style, but most of the linalool product appears to be converted to the pyranoid and furanoid linalool oxides. The LIS structural gene is a member of the …