Ethylene-Regulated Floral Volatile Synthesis in Petunia Corollas  

Abstract

In many flowering plants, such as petunia (Petunia 3 hybrida), ethylene produced in floral organs after pollination elicits a series of physiological and biochemical events, ultimately leading to senescence of petals and successful fertilization. Here, we demonstrate, using transgenic ethylene insensitive (44568) and Mitchell Diploid petunias, that multiple components of emission of volatile organic compounds (VOCs) are regulated by ethylene. Expression of benzoic acid/salicylic acid carboxyl methyltransferase (PhBSMT1 and 2) mRNA is temporally and spatially down-regulated in floral organs in a manner consistent with current models for postpollination ethylene synthesis in petunia corollas. Emission of methylbenzoate and other VOCs after pollination and exogenous ethylene treatment parallels a reduction in PhBSMT1 and 2 mRNA levels. Under cyclic light conditions (day/night), PhBSMT mRNA levels are rhythmic and precede emission of methylbenzoate by approximately 6 h. When shifted into constant dark or light conditions, PhBSMT mRNA levels and subsequent methylbenzoate emission correspondingly decrease or increase to minimum or maximum levels observed during normal conditions, thus suggesting that light may be a more critical influence on cyclic emission of methylbenzoate than a circadian clock. Transgenic PhBSMT RNAi flowers with reduced PhBSMT mRNA levels show a 75% to 99% decrease in methylbenzoate emission, with minimal changes in other petunia VOCs. These results implicate PhBSMT1 and 2 as genes responsible for synthesis of methylbenzoate in petunia.Many flowers exhibit a colorful display of petals and emit a complex mixture of floral volatile organic compounds (VOCs) that are together attractive to both pollinators and humans. Regulation of floral volatiles corresponds to pollinator activity times and receptivity of the flower to a pollination event (Dudareva et al., 2000;Schiestl and Ayasse, 2001). In many flowers, physiological changes take place following pollination and fertilization including petal wilting and abscission, color changes, flower closure, fruit development, and seed development (for review, see O'Neill, 1997). The plant hormone ethylene has been shown to coordinate several of these postpollination processes in many different plant species (van Doorn, 1997).In many plants, ethylene is synthesized and perceived in a localized, specific, and reproducible manner after pollination, underscoring the importance of understanding the progression of events and role of ethylene during pollination and fertilization. Petunia (Petunia 3 hybrida) is an excellent model system for studying postpollination responses because ethylene synthesis has been well characterized (Hoekstra and Weges, 1986;Tang and Woodson, 1996;Jones et al., 2003) and components of the ethylene-signaling pathway have been investigated (Wilkinson et al., 1997;Shibuya et al., 2004). In petunia, ethylene synchronizes pollen tube growth (Holden et al., 2003) and petal wilting (Hoekstra and Weges, 1986;Gubrium et al., 2000). An initial bur...

Unraveling the regulation of floral fragrance biosynthesis

“…12 Likewise, transcript accumulation from FVBP genes is greatly reduced by an exogenous ethylene signal. 12,13 FVBP biosynthesis and emission is specific to a tissue type (corolla limb), a developmental phase (receptive to fertilization, open flower), and can be molecularly and metabolically "turned off" by one phytohormone (ethylene). The commonality of regulation imparted upon the FVBP gene network enables the isolation of additional FVBP genes by screening candidates based on similarity of transcriptional regulation.…”

“…The vast majority of emitted FVBP compounds are detected from the corolla limb tissue of an open MD flower. 12,13 FVBP emission is greatly reduced by an endogenous ethylene signal upon a successful pollination biochemical steps directly producing volatile compounds (e.g., PHENYLACETALDEHYDE SYNTHASE (PhPAAS)), 4 to the identification of more structural biochemical steps located within the shikimate, phenylpropanoid and FVBP branch pathways (Fig. 1).…”

“…1,12,13 Therefore, it is reasonable to hypothesize the expression of genes responsible for the biosynthesis of emitted FVBP compounds is also organized and coordinated. When the transcript accumulation of seven genes involved in FVBP production were examined simultaneously through various dimensions of gene expression, a specific and coordinate gene regulation was obvious.…”

Mutagenesis in Petunia x hybrida Vilm. and isolation of a novel morphological mutant

“…Moreover, it is commercially important as ornamental, representing an output greater than US$148 million per year in the United States (USDA, 2005). Petunia is cultivated in flower beds and pots and requires full sunlight to produce plants and flowers with bright attractive colors, consistent with the prominent role of light in the regulation of several developmental and physiological processes, such as photomorphogenesis and seedling establishment and anthocyanin biosynthesis (Simkin et al, 2004;Underwood et al, 2005;Kanazawa et al, 2007).…”

Scent engineering: toward the goal of controlling how flowers smell

“…For example, in petunia flowers the endogenous benzoic acid/salicylic acid carboxyl methyltransferase (PhBSMT) apparently has higher catalytic efficiency with salicylic acid than benzoic acid, but the flowers do not emit methylsalicylate as a result of the small internal pool of free salicylic acid. Thus, the enzyme is responsible for the formation of methylbenzoate using the substantial amount of benzoic acid present within the cells [26,27] (Figure 1). Petunia flowers also emit low levels of benzyl acetate and phenylethyl acetate.…”