Terpenoids constitute one of the largest and most diverse classes of plant metabolites. While some terpenoids are involved in essential plant processes such as photosynthesis, respiration, growth, ...and development, others are specialized metabolites playing roles in the interaction of plants with their biotic and abiotic environment. Due to the distinct functions and properties of specific terpenoid compounds, there is a growing interest to introduce or modify their production in plants by metabolic engineering for agricultural, pharmaceutical, or industrial applications. The MVA and MEP pathways and the prenyltransferases providing the general precursors for terpenoid formation, as well as the enzymes of the various downstream metabolic pathways leading to the formation of different groups of terpenoid compounds have been characterized in detail in plants. In contrast, the molecular mechanisms directing the metabolic flux of precursors specifically toward one of several potentially competing terpenoid biosynthetic pathways are still not well understood. The formation of metabolons, multi-protein complexes composed of enzymes catalyzing sequential reactions of a metabolic pathway, provides a promising concept to explain the metabolic channeling that appears to occur in the complex terpenoid biosynthetic network of plants. Here we provide an overview about examples of potential metabolons involved in plant terpenoid metabolism that have been recently characterized and the first attempts to utilize metabolic channeling in terpenoid metabolic engineering. In addition, we discuss the gaps in our current knowledge and in consequence the need for future basic and applied research.
Graphical abstract Highlights ► Targeting enzymes to organelles with highest precursor pool affects product yield. ► Targeting of nonendogenous enzymes to organelles is a useful tool for engineering. ...► Identification of transporters is central for effective metabolic engineering. ► Advances in metabolomics of isolated organelles will impact engineering strategies. ► Future plant metabolic engineering will include introduction of entire pathways.
Terpenoids, compounds found in all domains of life, represent the largest class of natural products with essential roles in their hosts. All terpenoids originate from the five-carbon building blocks, ...isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP), which can be derived from the mevalonic acid (MVA) and methylerythritol phosphate (MEP) pathways. The absence of two components of the MVA pathway from archaeal genomes led to the discovery of an alternative MVA pathway with isopentenyl phosphate kinase (IPK) catalyzing the final step, the formation of IPP. Despite the fact that plants contain the complete classical MVA pathway, IPK homologs were identified in every sequenced green plant genome. Here, we show that IPK is indeed a member of the plant terpenoid metabolic network. It is localized in the cytosol and is coexpressed with MVA pathway and downstream terpenoid network genes.In planta,IPK acts in parallel with the MVA pathway and plays an important role in regulating the formation of both MVA and MEP pathway-derived terpenoid compounds by controlling the ratio of IP/DMAP to IPP/DMAPP. IP and DMAP can also competitively inhibit farnesyl diphosphate synthase. Moreover, we discovered a metabolically available carbon source for terpenoid formation in plants that is accessible viaIPKoverexpression. This metabolite reactivation approach offers new strategies for metabolic engineering of terpenoid production.
Tomato produces a number of terpenes in their glandular trichomes that contribute to host plant resistance against pests. While glandular trichomes of cultivated tomato
primarily accumulate a blend ...of monoterpenes, those of the wild tomato species
produce various sesquiterpenes. Recently, we have identified two groups of sesquiterpenes in
accessions that negatively affect the performance and choice behavior of the potato aphid (
). Aphids are piercing-sucking herbivores that use their mouthpart to penetrate and probe plant tissues in order to ultimately access vascular tissue and ingest phloem sap. Because secondary metabolites produced in glandular trichomes can affect the initial steps of the aphid feeding behavior, introducing the formation of defensive terpenes into additional plant tissues
metabolic engineering has the potential to reduce tissue penetration by aphids and in consequence virus transmission. Here, we have developed two multicistronic expression constructs based on the two sesquiterpene traits with activity toward
previously identified in
. Both constructs are composed of sequences encoding a prenyl transferase and a respective
terpene synthase, as well as enhanced green fluorescent protein as a visible marker. All three coding sequences were linked by short nucleotide sequences encoding the foot-and-mouth disease virus 2A self-processing oligopeptide which allows their co-expression under the control of one promoter. Transient expression of both constructs under the epidermis-specific
-promoter in tomato leaves demonstrated that formation of the two sets of defensive sesquiterpenes, β-caryophyllene/α-humulene and (-)-
-α-bergamotene/(+)-α-santalene/(+)-
-β-bergamotene, can be introduced into new tissues in tomato. The epidermis-specific transgene expression and terpene formation were verified by fluorescence microscopy and tissue fractionation with subsequent analysis of terpene profiles, respectively. In addition, the longevity and fecundity of
feeding on these engineered tomato leaves were significantly reduced, demonstrating the efficacy of this novel aphid control strategy.
Terpenoids emitted from snapdragon flowers include three monoterpenes derived from geranyl diphosphate (GPP), myrcene, (E)-β-ocimene and linalool, and a sesquiterpene, nerolidol, derived from ...farnesyl diphosphate (FPP). Using a functional genomics approach, we have isolated and biochemically characterized two nearly identical nerolidol/linalool synthases, AmNES/LIS-1 and AmNES/LIS-2, two enzymes responsible for the terpenoid profile of snapdragon scent remaining to be characterized. The AmNES/LIS-2 protein has an additional 30 amino acids in the N-terminus, and shares 95% amino acid sequence identity with AmNES/LIS-1, with only 23 amino acid substitutions distributed across the homologous regions of the proteins. Although these two terpene synthases have very similar catalytic properties, and synthesize linalool and nerolidol as specific products from GPP and FPP, respectively, they are compartmentally segregated. GFP localization studies and analysis of enzyme activities in purified leucoplasts, together with our previous feeding experiments, revealed that AmNES/LIS-1 is localized in cytosol, and is responsible for nerolidol biosynthesis, whereas AmNES/LIS-2 is located in plastids, and accounts for linalool formation. Our results show that subcellular localization of bifunctional enzymes, in addition to the availability of substrate, controls the type of product formed. By directing nearly identical bifunctional enzymes to more than one cellular compartment, plants extend the range of available substrates for enzyme utilization, thus increasing the diversity of the metabolites produced.
The invasive shrub glossy buckthorn (
) has been progressively colonizing the Northeastern United States and Southeastern Canada for more than a century. To determine the dominant arthropod orders ...and species associated with
, field surveys were conducted for two years across 16 plots within the Allegheny National Forest, Pennsylvania, USA. Statistical analyses were employed to assess the impact of seasonal variation on insect order richness and diversity. The comprehensive arthropod collection yielded 2845 insects and arachnids, with hemipterans comprising the majority (39.8%), followed by dipterans (22.3%) and arachnids (15.5%). Notably, 16.2% of the hemipterans collected were in the immature stages, indicating
as a host for development. The two dominant insect species of
were
(Hemiptera: Psyllidae) and
(Diptera: Drosophilidae);
utilized
fruits for reproduction. Species richness and diversity exhibited significant variations depending on the phenology of
. The profiles of volatile compounds emitted from the leaves and flowers of
were analyzed to identify factors that potentially contribute to the attraction of herbivores and pollinators. The results of our study will advance the development of novel
management strategies leveraging the insects associated with this invasive species.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Terpenoids are a large and diverse class of plant metabolites that also includes volatile mono- and sesquiterpenes which are involved in biotic interactions of plants. Due to the limited natural ...availability of these terpenes and the tight regulation of their biosynthesis, there is strong interest to introduce or enhance their production in crop plants by metabolic engineering for agricultural, pharmaceutical and industrial applications. While engineering of monoterpenes has been quite successful, expression of sesquiterpene synthases in engineered plants frequently resulted in production of only minor amounts of sesquiterpenes. To identify bottlenecks for sesquiterpene engineering in plants, we have used two nearly identical terpene synthases, snapdragon (
Antirrhinum majus
) nerolidol/linalool synthase-1 and -2 (AmNES/LIS-1/-2), that are localized in the cytosol and plastids, respectively. Since these two bifunctional terpene synthases have very similar catalytic properties with geranyl diphosphate (GPP) and farnesyl diphosphate (FPP), their expression in target tissues allows indirect determination of the availability of these substrates in both subcellular compartments. Both terpene synthases were expressed under control of the ripening specific
PG
promoter in tomato fruits, which are characterized by a highly active terpenoid metabolism providing precursors for carotenoid biosynthesis. As
AmNES/LIS-2
fruits produced the monoterpene linalool,
AmNES/LIS-1
fruits were found to exclusively produce the sesquiterpene nerolidol. While nerolidol emission in
AmNES/LIS-1
fruits was 60- to 584-fold lower compared to linalool emission in
AmNES/LIS-2
fruits, accumulation of nerolidol-glucosides in
AmNES/LIS-1
fruits was 4- to 14-fold lower than that of linalool-glucosides in
AmNES/LIS-2
fruits. These results suggest that only a relatively small pool of FPP is available for sesquiterpene formation in the cytosol. To potentially overcome limitations in sesquiterpene production, we transiently co-expressed the key pathway-enzymes hydroxymethylglutaryl-CoA reductase (HMGR) and 1-deoxy-D-xylulose 5-phosphate synthase (DXS), as well as the regulator isopentenyl phosphate kinase (IPK). While HMGR and IPK expression increased metabolic flux toward nerolidol formation 5.7- and 2.9-fold, respectively, DXS expression only resulted in a 2.5-fold increase.
Geranyl diphosphate (GPP), the precursor of many monoterpene end products, is synthesized in plastids by a condensation of dimethylallyl diphosphate and isopentenyl diphosphate (IPP) in a reaction ...catalyzed by homodimeric or heterodimeric GPP synthase (GPPS). In the heterodimeric enzymes, a noncatalytic small subunit (GPPS.SSU) determines the product specificity of the catalytic large subunit, which may be either an active geranylgeranyl diphosphate synthase (GGPPS) or an inactive GGPPS-like protein. Here, we show that expression of snapdragon (Antirrhinum majus) GPPS.SSU in tobacco (Nicotiana tabacum) plants increased the total GPPS activity and monoterpene emission from leaves and flowers, indicating that the introduced catalytically inactive GPPS.SSU found endogenous large subunit partner(s) and formed an active snapdragon/tobacco GPPS in planta. Bimolecular fluorescence complementation and in vitro enzyme analysis of individual and hybrid proteins revealed that two of four GGPPS-like candidates from tobacco EST databases encode bona fide GGPPS that can interact with snapdragon GPPS.SSU and form a functional GPPS enzyme in plastids. The formation of chimeric GPPS in transgenic plants also resulted in leaf chlorosis, increased light sensitivity, and dwarfism due to decreased levels of chlorophylls, carotenoids, and gibberellins. In addition, these transgenic plants had reduced levels of sesquiterpene emission, suggesting that the export of isoprenoid intermediates from the plastids into the cytosol was decreased. These results provide genetic evidence that GPPS.SSU modifies the chain length specificity of phylogenetically distant GGPPS and can modulate IPP flux distribution between GPP and GGPP synthesis in planta.
Over the last decade, the Allegheny National Forest (ANF) in the USA has experienced issues with the regeneration of black cherry (Prunus serotina). This study was conducted to investigate the ...effects of silvicultural treatment on the insect communities that may affect black cherry pollination and regeneration. We conducted a 2-year study to compare the abundance, richness, and diversity of insects in unmanaged, shelterwood seed-tree, and shelterwood clear-cut stands. Using pan traps, we sampled insects at the ground level and in the canopies of flowering mature black cherry trees. The results of this study showed significant increases in the abundance of insects captured in shelterwood seed-tree stands and in species richness and diversity of insects captured in the canopy of black cherry in shelterwood removal stands, indicating that silvicultural treatment affected the insect community significantly. The dominant insect order was Diptera (true flies, 72.91%, n = 12,668), and Anthalia bulbosa (Diptera: Hybotidae) was the dominant species comprising 33% of all insects found in the canopy of flowering black cherry. The findings in this study could help land managers in managing black cherry for its pollination and natural regeneration.
Summary
Aromatic l‐amino acid decarboxylases (AADCs) are key enzymes operating at the interface between primary and secondary metabolism. The Arabidopsis thaliana genome contains two genes, At2g20340 ...and At4g28680, encoding pyridoxal 5′‐phosphate‐dependent AADCs with high homology to the recently identified Petunia hybrida phenylacetaldehyde synthase involved in floral scent production. The At4g28680 gene product was recently biochemically characterized as an l‐tyrosine decarboxylase (AtTYDC), whereas the function of the other gene product remains unknown. The biochemical and functional characterization of the At2g20340 gene product revealed that it is an aromatic aldehyde synthase (AtAAS), which catalyzes the conversion of phenylalanine and 3,4‐dihydroxy‐l‐phenylalanine to phenylacetaldehyde and dopaldehyde, respectively. AtAAS knock‐down and transgenic AtAAS RNA interference (RNAi) lines show significant reduction in phenylacetaldehyde levels and an increase in phenylalanine, indicating that AtAAS is responsible for phenylacetaldehyde formation in planta. In A. thaliana ecotype Columbia (Col‐0), AtAAS expression was highest in leaves, and was induced by methyl jasmonate treatment and wounding. Pieris rapae larvae feeding on Col‐0 leaves resulted in increased phenylacetaldehyde emission, suggesting that the emitted aldehyde has a defensive activity against attacking herbivores. In the ecotypes Sei‐0 and Di‐G, which emit phenylacetaldehyde as a predominant flower volatile, the highest expression of AtAAS was found in flowers and RNAi AtAAS silencing led to a reduction of phenylacetaldehyde formation in this organ. In contrast to ecotype Col‐0, no phenylacetaldehyde accumulation was observed in Sei‐0 upon wounding, suggesting that AtAAS and subsequently phenylacetaldehyde contribute to pollinator attraction in this ecotype.
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