Hydrolysis of glycosidically bound volatiles from apple leaves (Cv. Anna) by Aspergillus niger beta-glucosidase affects the behavior of codling moth (Cydia pomonella L.)

Cytosolic Nudix Hydrolase 1 Is Involved in Geranyl β-Primeveroside Production in Tea

Geraniol is a potent tea odorant and exists mainly as geranyl glycoside in Camellia sinensis. Understanding the mechanisms of geraniol biosynthesis at molecular levels in tea plants is of great importance for practical improvement of tea aroma. In this study, geraniol and its glycosides from tea plants were examined using liquid chromatography coupled with mass spectrometry. Two candidate geraniol synthase (GES) genes (CsTPS) and two Nudix hydrolase genes (CsNUDX1-cyto and CsNUDX1-chlo) from the tea genome were functionally investigated through gene transcription manipulation and gene chemical product analyses. Our data showed that in tea leaves, levels of geranyl β-primeveroside were dramatically higher than those of geranyl β-glucoside, while free geraniol was undetectable in this study. A tempo-spatial variation of geranyl β-primeveroside abundance in tea plants existed, with high levels in young and green tissues and low levels in mature or non-green tissues. Cytosolic CsNUDX1-cyto showed higher hydrolysis activity of geranyl-pyrophosphate to geranyl-monophosphate (GP) in vitro than did chloroplastidial CsNUDX1-chlo. A transgenic study revealed that expression of CsNUDX1-cyto resulted in significantly more geranyl β-primeveroside in transgenic Nicotiana benthamiana compared with non-transgenic wild-type, whereas expression of CsNUDX1-chlo had no effect. An antisense oligo-deoxynucleotide study confirmed that suppression of CsNUDX1-cyto transcription in tea shoots led to a significant decrease in geranyl β-primeveroside abundance. Additionally, CsNUDX1-cyto transcript levels and geranyl β-primeveroside abundances shared the same tempo-spatial patterns in different organs in the tea cultivar "Shucha Zao," indicating that CsNUDX1-cyto is important for geranyl β-primeveroside formation in tea plants. Results also suggested that neither of the two candidate GES genes in tea plants did not function as GES in transgenic N. benthamiana. All our data indicated that CsNUDX1-cyto is involved in geranyl β-primeveroside production in tea plants. Our speculation about possible conversion from the chemical product of CsNUDX1-cyto to geranyl β-primeveroside in plants was also discussed.

Functional genomics reveals that a compact terpene synthase gene family can account for terpene volatile production in apple

Terpenes are specialized plant metabolites that act as attractants to pollinators and as defensive compounds against pathogens and herbivores, but they also play an important role in determining the quality of horticultural food products. We show that the genome of cultivated apple (Malus domestica) contains 55 putative terpene synthase (TPS) genes, of which only 10 are predicted to be functional. This low number of predicted functional TPS genes compared with other plant species was supported by the identification of only eight potentially functional TPS enzymes in apple 'Royal Gala' expressed sequence tag databases, including the previously characterized apple (E,E)-α-farnesene synthase. In planta functional characterization of these TPS enzymes showed that they could account for the majority of terpene volatiles produced in cv Royal Gala, including the sesquiterpenes germacrene-D and (E)-β-caryophyllene, the monoterpenes linalool and α-pinene, and the homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene. Relative expression analysis of the TPS genes indicated that floral and vegetative tissues were the primary sites of terpene production in cv Royal Gala. However, production of cv Royal Gala floral-specific terpenes and TPS genes was observed in the fruit of some heritage apple cultivars. Our results suggest that the apple TPS gene family has been shaped by a combination of ancestral and more recent genome-wide duplication events. The relatively small number of functional enzymes suggests that the remaining terpenes produced in floral and vegetative and fruit tissues are maintained under a positive selective pressure, while the small number of terpenes found in the fruit of modern cultivars may be related to commercial breeding strategies.

Main odorants in Jura flor-sherry wines. Relative contributions of sotolon, abhexon, and theaspirane-derived compounds

The aromatic profile of Jura flor-sherry wines (also called "yellow wines") has been little studied. Only acetaldehyde, diethoxy-1,1-ethane, and sotolon have been described as key odorants. In the present work, three wines (vintages 2002 and 2003) were investigated by gas chromatography-mass spectrometry and gas chromatography-olfactometry (GC-O) aroma extract dilution analysis. The goal was to assess the relative impact of varietal, fermentation, and oak-barrel compounds by using two complementary extraction procedures. No grape terpenoids were found after the long barrel aging (6 years and 3 months). On the other hand, two candy/fruity esters issued from yeast exhibited high flavor dilution factor (FD) values: ethyl isobutyrate (64-1024) and ethyl isovalerate (128-1024). As expected, many oak-related odorants were found in the XAD 2 flavor extracts, mainly homofuraneol [2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone] (cotton candy, FD = 16-256) and cis-β-methyloctalactone (butter, woody, FD = 256). Most probably issued from oxidation of the grape constituent theaspirane, an exceptional grenadine odor was perceived by GC-O up to dilution 64-1024. Chemical oxidation experiments and GC-high-resolution mass spectrometry (HRMS) allowed us to identify it as 4-hydroxy-7,8-dihydro-β-ionone (RI(CPsil5CB) = 1373), a hydrolysis-derived product of dihydrodehydro-β-ionone. With an extraction dedicated to hydrophilic compounds, the key role of sotolon was confirmed (112-387 μg/kg; FD = 256-1024). This procedure enabled us to also evidence its ethyl analogue, abhexon (31-74 μg/kg; FD = 64-256).

Enhanced β-ionone emission in Arabidopsis over-expressing AtCCD1 reduces feeding damage in vivo by the crucifer flea beetle

Plant carotenoid derived β-ionone has been shown to have diverse biological effects on some insect herbivores and herbivore parasitoids. In this study, Arabidopsis transgenic plants over-expressing a carotenoid cleavage dioxygenase1 gene (AtCCD1) were generated to test whether β-ionone emissions could be enhanced and used to control feeding by the crucifer flea beetle (Phyllotreta cruciferae Goeze). The transgenic plants exhibited a morphological phenotype indistinguishable from the wild type (WT) control over their complete life cycle. Gas chromatography and mass spectrometry analyses of headspace volatiles collected from 6-wk-old intact flowering plants revealed substantially enhanced β-ionone emission from transgenic plants compared with WT, but no β-ionone enhancement occurred at a young vegetative stage (4-wk-old seedlings). Bioassays in an enclosed environment showed that AtCCD1 over-expression resulted in ≍50% less leaf area damage by flea beetles on transgenic plants compared with WT plants. The mean number of damaged transgenic leaves per plant also was significantly lower in transgenic plants (P<0.05). Our results indicate that AtCCD1 over-expression and induced β-ionone emission might find application in the control of pests for Brassica crops grown in greenhouse operations. Potentially, β-ionone also could be used on crops grown in open-air ecosystems if this allomone is released in sufficient quantities to discourage herbivore foragers.