Biosynthesis of amphetamine analogs in plants

Amphetamine analogs are produced by plants in the genus Ephedra and by Catha edulis, and include the widely used decongestants and appetite suppressants pseudoephedrine and ephedrine. A combination of yeast (Candida utilis or Saccharomyces cerevisiae) fermentation and subsequent chemical modification is used for the commercial production of these compounds. The availability of certain plant biosynthetic genes would facilitate the engineering of yeast strains capable of de novo pseudoephedrine and ephedrine biosynthesis. Chemical synthesis has yielded amphetamine analogs with myriad functional group substitutions and diverse pharmacological properties. The isolation of enzymes with the serendipitous capacity to accept novel substrates could allow the production of substituted amphetamines in synthetic biosystems. Here, we review the biology, biochemistry and biotechnological potential of amphetamine analogs in plants.     

Searching for weed biocontrol agents—when to move on?

‘Classical’ biological control for an exotic weed requires time‐consuming and expensive surveys for natural enemies in the weed's native range. We advocate the use of rarefaction curves to improve survey efficiency, i.e. to determine the minimum sampling effort for discovering most of the potential control agents actually occurring in the weed's native range. Rarefaction (dilution) curves can be used to estimate the number of herbivore species expected on a given number of plants, at sampling sites or regions, using presence/absence data and species frequencies. An analysis of the shape of the rarefaction curves will therefore indicate (a) which sites possibly contain more undiscovered herbivore species and (b) whether sampling new sites is more likely to reveal further herbivores. This approach is illustrated with two case studies of insect surveys, of root and flower head feeders on Centaurea maculosa (Asteraceae) in Europe and for flower head feeders of various Asteraceae in Brazil. Finally, we consider consequences of combining this approach with focussed searches in the centre of endemism and propose a general survey protocol for natural enemies associated with a host plant in its native range.     

Integrating Economic Costs and Biological Traits into Global Conservation Priorities for Carnivores

Background

Prioritization schemes usually highlight species-rich areas, where many species are at imminent risk of extinction. To be ecologically relevant these schemes should also include species biological traits into area-setting methods. Furthermore, in a world of limited funds for conservation, conservation action is constrained by land acquisition costs. Hence, including economic costs into conservation priorities can substantially improve their conservation cost-effectiveness.

Methodology/Principal Findings

We examined four global conservation scenarios for carnivores based on the joint mapping of economic costs and species biological traits. These scenarios identify the most cost-effective priority sets of ecoregions, indicating best investment opportunities for safeguarding every carnivore species, and also establish priority sets that can maximize species representation in areas harboring highly vulnerable species. We compared these results with a scenario that minimizes the total number of ecoregions required for conserving all species, irrespective of other factors. We found that cost-effective conservation investments should focus on 41 ecoregions highlighted in the scenario that consider simultaneously both ecoregion vulnerability and economic costs of land acquisition. Ecoregions included in priority sets under these criteria should yield best returns of investments since they harbor species with high extinction risk and have lower mean land cost.

Conclusions/Significance

Our study highlights ecoregions of particular importance for the conservation of the world''s carnivores defining global conservation priorities in analyses that encompass socioeconomic and life-history factors. We consider the identification of a comprehensive priority-set of areas as a first step towards an in-situ biodiversity maintenance strategy.     

Flower-heads, herbivores, and their parasitoids: food web structure along a fertility gradient

Abstract. 1. The ways in which a soil fertility gradient affects three trophic level food webs defined by plants of the family Asteraceae, flower‐head herbivores, and their parasitoids was investigated. It was tested how the fertility gradient alters: (i) the abundance and richness of plants, herbivores, and their parasitoids, (ii) the herbivore–plant ratio, and (iii) the connectance of the plant–herbivore community matrix. 2. From April to May 2000, plants and insects were sampled in 16 Brazilian Cerrado (sensu stricto) sites along a physiognomic gradient varying from open shrublands (cerrado) to closed woodlands (cerradão). Sites were objectively positioned along the physiognomic gradient by a single index, tree density. Sixty‐seven per cent of the variation in tree density among sites was correlated to two principal components of a PCA, representing gradients of soil fertility. 3. Asteraceae abundance, richness, and flower‐head availability were negatively related to tree density due to their preference for sunny environments, despite the surplus of soil nutrients. The abundance and richness of Diptera and Lepidoptera, the most important flower‐head herbivores, were also negatively related to tree density. Parasitoid abundance decreased with tree density; however, the number of parasitoids per hosts was lower in cerrado, suggesting that top‐down forces are not getting stronger in more productive sites, as could be expected. 4. Community allometry analyses showed that the herbivore to plant ratio was independent of community richness and did not respond to tree density. 5. Connectance of the plant–herbivore matrix was dependent on the community matrix size. Proportionally, species‐rich cerrado sites had fewer interactions than their species‐poor counterparts. Nevertheless, after removing the effect of the matrix size, connectance was not related to tree density. 6. Soil fertility, as the primary cause of the cerrado–cerradão physiognomic gradient, strongly affected the abundance and richness of plants, herbivores and their parasitoids; however, it had little effect on important community attributes, such as the herbivore–plant ratio and the connectance of the plant–herbivore matrix.     

Four ways towards tropical herbivore megadiversity

Most multicellular species alive are tropical arthropods associated with plants. Hence, the host-specificity of these species, and their diversity at different scales, are keys to understanding the assembly structure of global biodiversity. We present a comprehensive scheme in which tropical herbivore megadiversity can be partitioned into the following components: (A) more host plant species per se , (B) more arthropod species per plant species, (C) higher host specificity of herbivores, or (D) higher species turnover (beta diversity) in the tropics than in the temperate zone. We scrutinize recent studies addressing each component and identify methodological differences among them. We find substantial support for the importance of component A, more tropical host species. A meta-analysis of published results reveals intermediate to high correlations between plant and herbivore diversity, accounting for up to 60% of the variation in insect species richness. Support for other factors is mixed, with studies too scarce and approaches too uneven to allow for quantitative summaries. More research on individual components is unlikely to resolve their relative contribution to overall herbivore diversity. Instead, we call for the adoption of more coherent methods that avoid pitfalls for larger-scale comparisons, for studies assessing different components together rather than singly, and for studies that investigate herbivore beta-diversity (component D) in a more comprehensive perspective.     

Whole blood interferon-gamma responses to mycobacterium tuberculosis antigens in young household contacts of persons with tuberculosis in Uganda

Background

Due to immunologic immaturity, IFN-γ-producing T cell responses may be decreased in young children compared to adults, thus we hypothesized that IFN-γ responses to mycobacterial antigens in household contacts exposed to Mycobacterium tuberculosis (Mtb) would be impaired in young children relative to adults. The objective of this study was to compare whole blood IFN-γ production in response to mycobacterial antigens between children and adults in Uganda.

Methodology/Principal Findings

We studied household contacts of persons with culture-positive pulmonary tuberculosis (TB) enrolled in a cohort study conducted in Kampala, Uganda. Whole blood IFN-γ production in response to Mtb culture-filtrate antigens was measured by ELISA and compared between infants (<2 years old, n = 80), young children (2 <5 years old, n = 216), older children (5 <15 years old, n = 443) and adults (≥15 years old, n = 528). We evaluated the relationship between IFN-γ responses and the tuberculin skin test (TST), and between IFN-γ responses and epidemiologic factors that reflect exposure to Mtb, and the effect of prior BCG vaccination on IFN-γ responses. Young household contacts demonstrated robust IFN-γ responses comparable to those of adults that were associated with TST and known risk factors for infection. There was no effect of prior BCG immunization on the IFN-γ response.

Conclusions/Significance

Young children in a TB endemic setting can mount robust IFN-γ responses generally comparable to those of adults, and as in adults, these responses correlated with the TST and known epidemiologic risk factors for Mtb infection.     

Small‐scale spatial autocorrelation and the interpretation of relationships between phenological parameters

Question: Are flower production and associated phenological variables (onset, end, duration, and three measures of flowering synchrony) randomly distributed in space or, alternatively, is there a neighbourhood structure (spatial autocorrelation) in the values of these variables? To which extent does spatial autocorrelation affect the correlation tests between phenological traits? Location: A tree savanna reserve in Southeastern Brazil (22°15′S,47°08′W). Methods: The flowering season of Chromolaena odorata was followed for all (96) individuals in a completely mapped area of 3000 m². The phenological traits were estimated by counting flower heads in anthesis on individual plants every seven days for 14 weeks. Results: Flowering time was unimodally distributed, but with different peak dates depending on whether individual flower heads or plants were counted. Three phenological traits and canopy closure above the plants showed some degree of spatial autocorrelation, which caused loss of up to 35% of degrees of freedom in nine of 36 correlation tests. Such a decrease in the degrees of freedom resulted in loss of significance for correlations in three pairs of variables. Conclusions: We hypothesize that the spatial autocorrelation in phenological traits between C. odorata neighbours may be driven by genetic similarity among neighbouring plants and/or spatial structuring of environmental factors. Because location and distance between samples may affect their statistical independence, we suggest that spatial autocorrelation should be taken into account in future studies of plant phenology, e.g. by using effective sample size in statistical tests.     

Biosynthesis of plant-derived flavor compounds

Plants have the capacity to synthesize, accumulate and emit volatiles that may act as aroma and flavor molecules due to interactions with human receptors. These low-molecular-weight substances derived from the fatty acid, amino acid and carbohydrate pools constitute a heterogenous group of molecules with saturated and unsaturated, straight-chain, branched-chain and cyclic structures bearing various functional groups (e.g. alcohols, aldehydes, ketones, esters and ethers) and also nitrogen and sulfur. They are commercially important for the food, pharmaceutical, agricultural and chemical industries as flavorants, drugs, pesticides and industrial feedstocks. Due to the low abundance of the volatiles in their plant sources, many of the natural products had been replaced by their synthetic analogues by the end of the last century. However, the foreseeable shortage of the crude oil that is the source for many of the artifical flavors and fragrances has prompted recent interest in understanding the formation of these compounds and engineering their biosynthesis. Although many of the volatile constituents of flavors and aromas have been identified, many of the enzymes and genes involved in their biosynthesis are still not known. However, modification of flavor by genetic engineering is dependent on the knowledge and availability of genes that encode enzymes of key reactions that influence or divert the biosynthetic pathways of plant-derived volatiles. Major progress has resulted from the use of molecular and biochemical techniques, and a large number of genes encoding enzymes of volatile biosynthesis have recently been reported.     

Citrus fruit bitter flavors: isolation and functional characterization of the gene Cm1,2RhaT encoding a 1,2 rhamnosyltransferase, a key enzyme in the biosynthesis of the bitter flavonoids of citrus

Species of the genus Citrus accumulate large quantities of flavanones that affect fruit flavor and have been documented to benefit human health. Bitter species, such as grapefruit and pummelo, accumulate bitter flavanone-7-O-neohesperidosides responsible, in part, for their characteristic taste. Non-bitter species, such as mandarin and orange, accumulate only tasteless flavanone-7-O-rutinosides. The key flavor-determining step of citrus flavanone-glycoside biosynthesis is catalyzed by rhamnosyltransferases; 1,2 rhamnosyltransferases (1,2RhaT) catalyze biosynthesis of the bitter neohesperidosides, while 1,6 rhamnosyltransferases (1,6RhaT) catalyze biosynthesis of the tasteless rutinosides. We report on the isolation and functional characterization of the gene Cm1,2RhaT from pummelo which encodes a citrus 1,2RhaT. Functional analysis of Cm1,2RhaT recombinant enzyme was conducted by biotransformation of the substrates using transgenic plant cell culture. Flavanones and flavones, but not flavonols, were biotransformed into 7-O-neohesperidosides by the transgenic BY2 tobacco cells expressing recombinant Cm1,2RhaT. Immunoblot analysis established that 1,2RhaT protein was expressed only in the bitter citrus species and that 1,6RhaT enzyme, whose activity was previously documented in non-bitter species, was not cross-reactive. Expression of Cm1,2RhaT at the RNA level was prominent in young fruit and leaves, but low in the corresponding mature tissue, thus correlating well with the developmental pattern of accumulation of flavanone-neohesperidosides previously established. Phylogenetic analysis of the flavonoid glycosyltransferase gene family places Cm1,2RhaT on a separate gene cluster together with the only other functionally characterized flavonoid-glucoside rhamnosyltransferase gene, suggesting a common evolutionary origin for rhamnosyltransferases specializing in glycosylation of the sugar moieties of flavonoid glucosides.