Metabolic analysis of the interaction between plants and herbivores

Insect herbivores by necessity have to deal with a large arsenal of plant defence metabolites. The levels of defence compounds may be increased by insect damage. These induced plant responses may also affect the metabolism and performance of successive insect herbivores. As the chemical nature of induced responses is largely unknown, global metabolomic analyses are a valuable tool to gain more insight into the metabolites possibly involved in such interactions. This study analyzed the interaction between feral cabbage (Brassica oleracea) and small cabbage white caterpillars (Pieris rapae) and how previous attacks to the plant affect the caterpillar metabolism. Because plants may be induced by shoot and root herbivory, we compared shoot and root induction by treating the plants on either plant part with jasmonic acid. Extracts of the plants and the caterpillars were chemically analysed using Ultra Performance Liquid Chromatography/Time of Flight Mass Spectrometry (UPLCT/MS). The study revealed that the levels of three structurally related coumaroylquinic acids were elevated in plants treated on the shoot. The levels of these compounds in plants and caterpillars were highly correlated: these compounds were defined as the ‘metabolic interface’. The role of these metabolites could only be discovered using simultaneous analysis of the plant and caterpillar metabolomes. We conclude that a metabolomics approach is useful in discovering unexpected bioactive compounds involved in ecological interactions between plants and their herbivores and higher trophic levels.

Impact of foliar herbivory on the development of a root-feeding insect and its parasitoid

The majority of studies exploring interactions between above- and below-ground biota have been focused on the effects of root-associated organisms on foliar herbivorous insects. This study examined the effects of foliar herbivory by Pieris brassicae L. (Lepidoptera: Pieridae) on the performance of the root herbivore Delia radicum L. (Diptera: Anthomyiidae) and its parasitoid Trybliographa rapae (Westwood) (Hymenoptera: Figitidae), mediated through a shared host plant Brassica nigra L. (Brassicaceae). In the presence of foliar herbivory, the survival of D. radicum and T. rapae decreased significantly by more than 50%. In addition, newly emerged adults of both root herbivores and parasitoids were significantly smaller on plants that had been exposed to foliar herbivory than on control plants. To determine what factor(s) may have accounted for the observed results, we examined the effects of foliar herbivory on root quantity and quality. No significant differences in root biomass were found between plants with and without shoot herbivore damage. Moreover, concentrations of nitrogen in root tissues were also unaffected by shoot damage by P. brassicae larvae. However, higher levels of indole glucosinolates were measured in roots of plants exposed to foliar herbivory, suggesting that the development of the root herbivore and its parasitoid may be, at least partly, negatively affected by increased levels of these allelochemicals in root tissues. Our results show that foliar herbivores can affect the development not only of root-feeding insects but also their natural enemies. We argue that such indirect interactions between above- and below-ground biota may play an important role in the structuring and functioning of communities

Differences in Volatile Profiles of Turnip Plants Subjected to Single and Dual Herbivory Above- and Belowground

Plants attacked by herbivorous insects emit volatile organic compounds that are used by natural enemies to locate their host or prey. The composition of the blend is often complex and specific. It may vary qualitatively and quantitatively according to plant and herbivore species, thus providing specific information for carnivorous arthropods. Most studies have focused on simple interactions that involve one species per trophic level, and typically have investigated the aboveground parts of plants. These investigations need to be extended to more complex networks that involve multiple herbivory above- and belowground. A previous study examined whether the presence of the leaf herbivore Pieris brassicae on turnip plants (Brassica rapa subsp. rapa) influences the response of Trybliographa rapae, a specialist parasitoid of the root feeder Delia radicum. It showed that the parasitoid was not attracted by volatiles emitted by plants under simultaneous attack. Here, we analyzed differences in the herbivore induced plant volatile (HIPV) mixtures that emanate from such infested plants by using Orthogonal Partial Least Squares-Discriminant Analysis (OPLS-DA). This multivariate model focuses on the differences between odor blends, and highlights the relative importance of each compound in an HIPV blend. Dual infestation resulted in several HIPVs that were present in both isolated infestation types. However, HIPVs collected from simultaneously infested plants were not the simple combination of volatiles from isolated forms of above- and belowground herbivory. Only a few specific compounds characterized the odor blend of each type of damaged plant. Indeed, some compounds were specifically induced by root herbivory (4-methyltridecane and salicylaldehyde) or shoot herbivory (methylsalicylate), whereas hexylacetate, a green leaf volatile, was specifically induced after dual herbivory. It remains to be determined whether or not these minor quantitative variations, within the background of more commonly induced odors, are involved in the reduced attraction of the root feeder’s parasitoid. The mechanisms involved in the specific modification of the odor blends emitted by dual infested turnip plants are discussed in the light of interferences between biosynthetic pathways linked to plant responses to shoot or root herbivory

Testing the paradox of enrichment along a land use gradient in a multitrophic aboveground and belowground community

In the light of ongoing land use changes, it is important to understand how multitrophic communities perform at different land use intensities. The paradox of enrichment predicts that fertilization leads to destabilization and extinction of predator-prey systems. We tested this prediction for a land use intensity gradient from natural to highly fertilized agricultural ecosystems. We included multiple aboveground and belowground trophic levels and land use-dependent searching efficiencies of insects. To overcome logistic constraints of field experiments, we used a successfully validated simulation model to investigate plant responses to removal of herbivores and their enemies. Consistent with our predictions, instability measured by herbivore-induced plant mortality increased with increasing land use intensity. Simultaneously, the balance between herbivores and natural enemies turned increasingly towards herbivore dominance and natural enemy failure. Under natural conditions, there were more frequently significant effects of belowground herbivores and their natural enemies on plant performance, whereas there were more aboveground effects in agroecosystems. This result was partly due to the “boom-bust” behavior of the shoot herbivore population. Plant responses to herbivore or natural enemy removal were much more abrupt than the imposed smooth land use intensity gradient. This may be due to the presence of multiple trophic levels aboveground and belowground. Our model suggests that destabilization and extinction are more likely to occur in agroecosystems than in natural communities, but the shape of the relationship is nonlinear under the influence of multiple trophic interactions.

Identification of Biologically Relevant Compounds in Aboveground and Belowground Induced Volatile Blends

Plants under attack by aboveground herbivores emit complex blends of volatile organic compounds (VOCs). Specific compounds in these blends are used by parasitic wasps to find their hosts. Belowground induction causes shifts in the composition of aboveground induced VOC blends, which affect the preference of parasitic wasps. To identify which of the many volatiles in the complex VOC blends may explain parasitoid preference poses a challenge to ecologists. Here, we present a case study in which we use a novel bioinformatics approach to identify biologically relevant differences between VOC blends of feral cabbage (Brassica oleracea L.). The plants were induced aboveground or belowground with jasmonic acid (JA) and shoot feeding caterpillars (Pieris brassicae or P. rapae). We used Partial Least Squares—Discriminant Analysis (PLSDA) to integrate and visualize the relation between plant-emitted VOCs and the preference of female Cotesia glomerata. Overall, female wasps preferred JA-induced plants over controls, but they strongly preferred aboveground JA-induced plants over belowground JA-induced plants. PLSDA revealed that the emission of several monoterpenes was enhanced similarly in all JA-treated plants, whereas homoterpenes and sesquiterpenes increased exclusively in aboveground JA-induced plants. Wasps may use the ratio between these two classes of terpenes to discriminate between aboveground and belowground induced plants. Additionally, it shows that aboveground applied JA induces different VOC biosynthetic pathways than JA applied to the root. Our bioinformatic approach, thus, successfully identified which VOCs matched the preferences of the wasps in the various choice tests. Additionally, the analysis generated novel hypotheses about the role of JA as a signaling compound in aboveground and belowground induced responses in plants

Coalescent-based genome analyses resolve the early branches of the euarchontoglires

Despite numerous large-scale phylogenomic studies, certain parts of the mammalian tree are extraordinarily difficult to resolve. We used the coding regions from 19 completely sequenced genomes to study the relationships within the super-clade Euarchontoglires (Primates, Rodentia, Lagomorpha, Dermoptera and Scandentia) because the placement of Scandentia within this clade is controversial. The difficulty in resolving this issue is due to the short time spans between the early divergences of Euarchontoglires, which may cause incongruent gene trees. The conflict in the data can be depicted by network analyses and the contentious relationships are best reconstructed by coalescent-based analyses. This method is expected to be superior to analyses of concatenated data in reconstructing a species tree from numerous gene trees. The total concatenated dataset used to study the relationships in this group comprises 5,875 protein-coding genes (9,799,170 nucleotides) from all orders except Dermoptera (flying lemurs). Reconstruction of the species tree from 1,006 gene trees using coalescent models placed Scandentia as sister group to the primates, which is in agreement with maximum likelihood analyses of concatenated nucleotide sequence data. Additionally, both analytical approaches favoured the Tarsier to be sister taxon to Anthropoidea, thus belonging to the Haplorrhine clade. When divergence times are short such as in radiations over periods of a few million years, even genome scale analyses struggle to resolve phylogenetic relationships. On these short branches processes such as incomplete lineage sorting and possibly hybridization occur and make it preferable to base phylogenomic analyses on coalescent methods

The effects of caffeinated and decaffeinated coffee on sex hormone-binding globulin and endogenous sex hormone levels: A randomized controlled trial

10.1186/1475-2891-11-86Nutrition Journal111

Defensive properties of pyrrolizidine alkaloids against microorganisms

The understanding of the selection factors that drive chemical diversification of secondary metabolites of constitutive defence systems in plants, such as pyrrolizidine alkaloids (PAs), is still incomplete. Historically, plants always have been confronted with microorganisms. Long before herbivores existed on this planet, plants had to cope with microbial pathogens. Therefore, plant pathogenic microorganisms may have played an important role in the early evolution of the secondary metabolite diversity. In this review, we discuss the impact that plant-produced PAs have on plant-associated microorganisms. The objective of the review is to present the current knowledge on PAs with respect to anti-microbial activities, adaptation and detoxification by microorganisms, pathogenic fungi, root protection and PA induction. Many in vitro experiments showed effects of PAs on microorganisms. These results point to the potential of microorganisms to be important for the evolution of PAs. However, only a few in vivo studies have been published and support the results of the in vitro studies. In conclusion, the topics pointed out in this review need further exploration by carrying out ecological experiments and field studies

Molecular and life-history effects of a natural toxin on herbivorous and non-target soil arthropods

Natural toxins, such as isothiocyanate (ITC), are harmful secondary metabolites produced by plants. Many natural toxins occur in commercial crops, yet their possible negative repercussions on especially non-target soil organisms are largely unknown. This study examined life-history and gene transcriptional responses to 2-phenylethyl ITC on two soil arthropod species: Folsomia candida and Protaphorura fimata. To that end the standardized ISO guideline for ecotoxicological tests and a microarray for F. candida were used. The dissipation of 2-phenylethyl ITC in natural soil was investigated using GC-MS/MS for quantification. Half-lives, tested at four concentration levels in natural soil, were on average 16 h with biodegradation as the plausible main removal process. Regardless, toxic effects on reproduction were shown for F. candida and P. fimata, with EC50 values of around 11.5 nmol/g soil illustrating the toxic character of this compound. Gene expression profiles revealed the importance of fatty acid metabolism at low exposure concentrations (EC10), which is associated with the lipophilic nature of 2-phenylethyl ITC. At higher concentrations (EC50) gene expression became more ubiquitous with over-expression of especially stress-related genes and sugar metabolism. The regulation of a gene encoding a precursor of follistatin, furthermore, implied the inhibition of reproduction and may be an important molecular target that can be linked to the observed adverse effect of life-history traits