Floral Scent Production in Clarkia breweri (Onagraceae) (II. Localization and Developmental Modulation of the Enzyme S-Adenosyl-L-Methionine:(Iso)Eugenol O-Methyltransferase and Phenylpropanoid Emission)

Abstract

Here we report that petal tissue was responsible for the bulk of the phenylpropanoid emission. The activity of S-adenosyl-i-methionine:(iso)eugenol O-methyltransferase (IEMT), a nove1 enzyme that catalyzes the methylation of the para-4'-hydroxyl of both eugenol and (iso)eugenol to methyleugenol and isomethyleugenol, respectively, was also highest i n petal tissue. IEMT activity was absent from floral tissues of plants not emitting (iso)methyleugenol. A C. breweri cDNA clone encoding IEMT was isolated, and its sequence was shown t o have 70% identity t o S-adenosyl-L-methionine:caffeic acid Omethyltransferase. l h e protein encoded by this cDNA can use eugenol and isoeugenol as substrates, but not caffeic acid. Steadystate IEMT mRNA levels were positively correlated with levels of IEMT activity in the tissues, and no IEMT mRNA was observed in flowers that do not emit (iso)methyleugenol. Overall, the data show that the floral emission of (iso)methyleugenol is controlled at the site of emission, that a positive correlation exists between volatile emission and IEMT activity, and that control of the level of IEMT activity is exerted at a pretranslational step.Flowers of many plants attract pollinators by producing and emitting a complex mixture of low-molecular-weight volatile compounds. Floral scents may function as both long-and short-distance attractants and nectar guides to a variety of animal pollinators (for review, see Dobson, 1993). Since insects are able to distinguish between complex floral scent mixtures, discriminatory visitation based on floral scent has important implications for population structure and reproductive isolation (Dodson et al

Biosynthesis of plant‐derived flavor compounds

“…Various OMTs involved in the biosynthetic pathways of floral scent components have been identified and characterized. For example, S-adenosyl-L-methionine (iso)eugenol OMT, which catalyzes the methylation of eugenol and isoeugenol to form the volatiles methyleugenol and isomethyleugenol, has been isolated from Clarkia breweri (Wang et al, 1997). Eugenol OMT and chavicol OMT, which convert eugenol and chavicol to methyleugenol and methylchavicol, respectively, have been identified in Ocimun basilicum (Gang et al, 2002;Lewinsohn et al, 2000).…”

Character coding of secondary chemical variation for use in phylogenetic analyses

“…In the case of isoeugenol O-methyl transferase (IEMT), only 7 amino acid substitutions were required to cause a diverged function from the precursor, ca!eic acid O-methyl transferase (COMT) (Wang and Pichersky, 1999). Transcriptional and translational regulatory integration into a tissue speci"c biochemical pathway must have then occurred (Wang et al, 1997;Nam et al, 1999). Finally, evolution of osmophores might occur, but there is evidence that this may not be necessary, at least in Clarkia breweri (Raguso and Pichersky, 1995).…”

“…Consider, Clarkia breweri, the best studied example of an evolutionary gain of fragrance production (Pichersky et al, 1994;Raguso and Pichersky, 1995;Wang and Pichersky, 1998;Dudareva et al, 1998;Wang et al, 1997;Wang and Pichersky, 1999;Ross et al, 1999;Raguso and Pichersky, 1999). In this species, the initial steps of fragrance evolution required gene duplication and divergence.…”

“…Experimental studies have shown that absence of scent in otherwise scent producing species or their close relatives may occur due to complete gene absence (Yuba et al, 1996), gene presence but lack of transcription (Wang et al, 1997), and gene presence with transcription but lack of enzyme function due to point mutations of critical amino acids (Dudareva, pers. comm.).…”

A Stress-Inducible Resveratrol O-Methyltransferase Involved in the Biosynthesis of Pterostilbene in Grapevine

“…Stilbene quantifications showed leaf-to-leaf variations, probably due to differences in leaf developmental stages because maturity has been shown to influence P. viticola infection (Liu et al, 2003). A number of plant OMTs have been characterized using biochemical approaches (He and Dixon, 1996;Wang et al, 1997;Chiron et al, 2000a;Dudareva et al, 2000;Wu et al, 2004). These strategies typically involved enzyme purification and sequencing of peptides derived from the purified protein.…”