The bouquet of grapevine (Vitis viniferaL. cv. Cabernet Sauvignon) flowers arises from the biosynthesis of sesquiterpene volatiles in pollen grains

Abstract

Terpenoid volatiles are important information molecules that enable pollinators to locate flowers and may protect reproductive tissues against pathogens or herbivores. Inflorescences of grapevine (Vitis vinifera L.) are composed of tiny green flowers that produce an abundance of sesquiterpenoid volatiles. We demonstrate that male flower parts of grapevines are responsible for sesquiterpenoid floral scent formation. We describe temporal and spatial patterns of biosynthesis and release of floral volatiles throughout the blooming of V. vinifera L. cv. Cabernet Sauvignon. The biosynthesis of sesquiterpene volatiles, which are emitted with a light-dependent diurnal pattern early in the morning at prebloom and bloom, is localized to anthers and, more specifically, within the developing pollen grains. Valencene synthase (VvValCS) enzyme activity, which produces the major sesquiterpene volatiles of grapevine flowers, is present in anthers. VvValCS transcripts are most abundant in flowers at prebloom stages. Western blot analysis identified VvValCS protein in anthers, and in situ immunolabeling located VvValCS protein in pollen grains during bloom. Histochemical staining, as well as immunolabeling analysis by fluorescent microscopy and transmission electron microscopy, indicated that VvValCS localizes close to lipid bodies within the maturing microspore.anthers ͉ floral scent ͉ flower development ͉ sesquiterpenes ͉ terpenoid biosynthesis A lthough the release of volatiles, including aliphatics, terpenoids, and phenylpropanoids, from anthers and/or pollen has been reported (1), the molecular mechanisms and localization of pollen volatile formation remain uncertain. Pollen volatiles serve as attractants for pollinators and also may function to deter herbivores and defend against pathogens (2). They can be distinct from the scents of other floral organs and may decrease after pollination, thereby advertising the pollen of unvisited flowers to pollinators (1, 3). Pollen volatiles are thought to be localized to the pollenkitt, a waxy substance localized to the grooves in the exine, which provides protection against pathogens, desiccation, or UV light and assists in pollen-pistil interactions (1, 4). Various nonvolatile compounds of the pollenkitt and sporopollenin are deposited on the surface of microspores by tapetum cells (4). Although it has been postulated that the tapetum also produces volatiles (1, 5), this has not been established experimentally.Grapevines produce dense panicles of small flowers with tiny petals fused into a cap (Fig. 1). Most cultivated grapevines have perfect hermaphroditic flowers and are thought to be at least partially autogamous or cleistogamous (6), whereas their wild relatives are dioecious and have functionally pistillate or staminate flowers that require insect pollinators for fertilization (7,8). The composition of floral volatiles of several cultivated grapevine varieties has been described (9-11), but little else is known about the molecular biochemistry of grapevine floral scent. Research...

Variation of Herbivore-Induced Volatile Terpenes among Arabidopsis Ecotypes Depends on Allelic Differences and Subcellular Targeting of Two Terpene Synthases, TPS02 and TPS03

“…The specific expression profile of TPS03 in the stigma and sepal of Col-0 flowers may reflect the functions of (E,E)-a-farnesene in pollinator attraction or florivore/ antimicrobial defense, as discussed for the flowerspecific genes TPS21 [encoding a (E)-b-caryophyllene synthase; Tholl et al, 2005] and TPS24 (a multiproduct monoterpene synthase), which exhibit similar expression patterns in Arabidopsis flowers (Chen et al, 2003b). Interestingly, TPS03 promoter activity was observed in pollen grains and resembles the recently reported expression of a valencene sesquiterpene synthase in the pollen of grape (Vitis vinifera) flowers (Martin et al, 2009). A pattern of constitutive expression in reproductive organs and induced expression in vegetative tissues has also been observed for Arabidopsis geranyllinalool synthase (TPS04/GES; Herde et al, 2008) in the formation of the volatile homoterpene TMTT and has been demonstrated for other genes involved in plant defense (Pollak et al, 1993;Hoegen et al, 2002;Stotz et al, 2009).…”

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