Analysis of behavioral and electrophysiological responses to alfalfa floral VOC chemistry revealed that honeybees, while ignoring major scent compounds e. As alfalfa flowers also emit deterrents, a generation of new cultivars with elevated emission of attractants and simultaneously suppressed emission of repellants will enhance honeybee visitations to alfalfa.
Another example includes glasshouse tomato production, where imported bumblebees are routinely used as pollinators, but preferentially forage on other flowering plants outside the glasshouse. Moreover, many modern crop cultivars are deficient in VOC production as a result of breeding for increased growth or yield which negatively affects secondary metabolism, including VOCs. Indeed, flowers produced by horticultural cultivars of cacao Theobroma cacao are small, barely fragrant, and only attract opportunistic flies that are inefficient pollinators, whereas wild Theobroma sp.
Similar trends were observed for vegetative VOCs Fig. Cranberry, for example, is only one or two crosses away from its wild progenitor, Vaccinium sp. Taken together, these examples show that crop VOCs are poorly adapted to maintain beneficial insects in agricultural systems. In the past decade, numerous attempts have been made to modulate plant volatile profiles and to investigate the effect of changes in volatile emission on insect behavior Fig.
Moreover, the effect of modified VOC profiles on plant defense needs to be evaluated in an agricultural setting. Monitoring the activity of floral visitors in their native habitat revealed that plants lacking benzyl acetone attracted fewer hawkmoths and hummingbirds than flowers emitting this volatile. It was also shown that changes in more than one volatile compound can influence pollinator behavior.
While the most highly abundant volatile methylbenzoate acted as both attractant and deterrent, isoeugenol and benzylbenzoate only exhibited the latter function. Several attempts have been made to improve the flavor of tomato fruits Fig. While humans were able to assess changes in fruit aroma, the effect of these genetic manipulations on fruit dispersers has not been investigated.
Overall, the studies described have demonstrated the potential of metabolic engineering of VOCs for both the improvement of plant defense and pollinator attraction Fig. Further, ecological complications will arise once these methodological constraints are lifted. In the wild gourd, Cucurbita pepo var. Given that C. A comprehensive understanding of plant metabolic networks and their regulation, as well as knowledge about key compounds involved in plant—insect interactions in the near future, will greatly advance metabolic engineering of VOCs and help to overcome these challenges.
Current advances in chemical ecology highlight the importance of plant VOCs in natural ecosystems as crucial signaling molecules in plant defense, pollination and plant—plant communication.
Recent breakthroughs in scent gene discovery and metabolic engineering make it possible to manipulate the amount of specific volatiles in planta , either omitting or increasing their emission, thus greatly facilitating the identification of key attractants for pollinators and natural enemies. Unfortunately, our limited current understanding of the regulation of VOC biosynthetic pathways constrains the manipulation of VOC emission for enhanced pollination and sustainable pest management strategies based on biological control.
The identification of transcription factors that regulate the orchestrated emission of volatiles originating from different metabolic pathways will significantly improve our success. Nevertheless, future attempts to increase crop yield will necessitate collaborative efforts by ecologists, entomologists, agronomists, biochemists and plant metabolic engineers.
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These effects may be unavoidable because most VOCs have multiple functions in plants. Enhancing crop—pollinator interactions becomes even more critical for modern agriculture, which is facing sudden declines in honeybee populations and is thus increasingly dependent on native bees.
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Metabolic engineering of plant secondary metabolism
Abstract 2 16 I. Summary Plants synthesize an amazing diversity of volatile organic compounds VOCs that facilitate interactions with their environment, from attracting pollinators and seed dispersers to protecting themselves from pathogens, parasites and herbivores. Biosynthesis of volatile plant secondary metabolites and its interconnection with primary metabolism A relatively large group of plant natural products consists of volatile organic compounds VOCs , lipophilic liquids with low molecular weight and high vapor pressure at ambient temperatures.
Figure 1 Open in figure viewer PowerPoint. Overview of biosynthetic pathways leading to the emission of plant volatile organic compounds VOCs. Precursors for plant VOCs originate from primary metabolism represented in the blue box. Stacked arrows illustrate the involvement of multiple enzymatic reactions.
VOCs are highlighted with a purple cloud as background. Figure 2 Open in figure viewer PowerPoint.
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Synthesis of terpenoid volatile organic compounds VOCs. Terpenoid VOCs are synthesized by the cytosolic mevalonic acid MVA and the plastidial methylerythritol phosphate MEP pathways, the former giving rise to sesquiterpenes, irregular terpenes and geranyllinalool, and the latter to monoterpenes, hemiterpenes, diterpenes and volatile carotenoid derivatives. Solid arrows represent established biosynthetic steps, whereas broken arrows point to hypothetical reactions.
Volatile terpenoid compounds are highlighted with a purple cloud as background. Enzymes shown in blue exhibit peroxisomal localization, whereas the one in red is localized at the endoplasmic reticulum ER. Figure 3 Open in figure viewer PowerPoint. Synthesis of benzenoid and phenylpropanoid volatile organic compounds VOCs. Solid arrows indicate established biochemical steps, while hypothetical steps not yet described are represented by broken arrows.
Figure 4 Open in figure viewer PowerPoint. Volatile compounds are highlighted with a colored background, with green leaf volatiles shown in green. Figure 5 Open in figure viewer PowerPoint.
Secondary metabolism and metabolic engineering (/)faxarytogy.tkhnology-University of Verona
The aldehyde can be synthesized by decarboxylation of the amino acid followed by deamination; by direct synthesis of the aldehyde; and by transamination of the amino acid followed by a carboxylation. The aldehyde is further converted to a variety of VOCs with diverse functional groups. TCA, tricarboxylic acid.
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Regulation of volatile emission in plants In plants, formation of VOCs is spatially regulated. Figure 6 Open in figure viewer PowerPoint. Role of floral volatile organic compounds VOCs in reproductive isolation. Floral VOCs are an essential component in this isolation. Impact of floral VOCs on agriculture Unlike predators and parasitic wasps whose functional roles could be substituted by chemical insecticides, pollinators cannot be readily replaced.
Figure 7 Open in figure viewer PowerPoint. A list of central questions that should be addressed in future research efforts to enhance crop pollination by manipulating composition of floral volatile organic compounds VOCs. Clipart images used with permission from Microsoft. Figure 8 Open in figure viewer PowerPoint. The goal of this project is to engineer Saccharomyces cerevisiae for the sustainable production of high value and industrially relevant plant secondary metabolites, such as pigments natural colours , terpenes and plant hormones.
To achieve this goal, we first identify the plant biosynthetic pathway leading to our compound of interest. Then we introduce this pathway in S. Subsequently, we will ferment the newly developed S. Further rounds of engineering might be required to improve productivity of these strains. In addition to an industrial application, expression of these plant enzymes in yeast will also provide us insight in how and why these compounds are produced in plants.
We make use of the latest methods in molecular biology, metabolic engineering e. Go directly to: Content Search box Breadcrumb.
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