Tribes Of Asteraceae Research Articles

Phylogenetic Distribution of DMV-D10, an Endogenous Strain of Dahlia Mosaic Virus, in Members of Asteraceae

DMV-D10 is a strain of Dahlia mosaic virus (DMV) that is classified as an endogenous virus and does not induce any visible symptoms in the host plant. Endogenous viruses have the ability to integrate their viral sequences into the host plant genome, which can be transmitted to offspring. No studies have examined the host range of DMV-D10 outside of the Dahlia genus. Because DMV-D10 has only been observed in Dahlia, the objective for this study was to determine if presence of DMV-D10 follows an evolutionary relationship among species closely related to Dahlia. An addition objective of this study was to determine if species infected with DMV-D10 may also be infected with Dahlia common mosaic virus (DCMV) because these plant viruses are closely related. It was hypothesized species in the same tribe (Coreopsideae) as Dahlia were more likely to be infected with DMV-D10 compared to species in other Asteraceae tribes. Ten tribes consisting of thirty-five species were collected, and DNA was extracted to determine DMV-D10 infection. Polymerase chain reaction (PCR) results for a movement protein gene indicate DMV-D10 is widely spread across Asteraceae. Specifically, gel electrophoresis results suggest presence of DMV-D10 in thirteen species across seven tribes. Additionally, DCMV was detected in six species across five tribes of Asteraceae. Although, phylogenetic relationship of host plants does not necessarily determine DMV-D10 infection. This leads to questions of how this virus can move to species in other Asteraceae tribes. Some potential hypotheses include pollen transmission or possible plant-virus coevolution.

A survey of ontogeny cypsela characters contributing to the infrafamilial characterization of Asteraceae

Structural features of cypsela are important to certain tribes of Asteraceae; thus, the ontogeny of the fruit (only the pericarp) of 10 weedy Asteraceae species was determined concerning the contribution to increase the knowledge of the fruit development in Asteraceae. The species analyzed are Conyza bonariensis L. (Cronquist.), Cosmos sulphureus Cav., Eclipta alba L. Hassk., Elephantopus mollis Kunth., Emilia sonchifolia L. DC., Galinsoga quadriradiata Ruiz & Pav., Erechtites valerianifolius (Wolf) DC., Parthenium hysterophorus L., Praxelis clematidea (Griseb) R.M. King & H. Rob and Sigesbeckia orientalis L. The mesocarp in the cypsela structure shows variation in the number of layers, the cell layer arrangement of the sclerenchyma and parenchyma, and the presence of phytomelanin that is especially striking. The mesocarp traits of Heliantheae alliance species are homogeneous, and it has been suggested that the derived character phytomelanin may not have the same evolutionary history in species belonging to the same tribe. It is noteworthy that Cichorioideae cypsela has the same general structure as that of Asteroideae.

Powdery mildew of Chrysanthemum × morifolium: phylogeny and taxonomy in the context of Golovinomyces species on Asteraceae hosts

ABSTRACTThe taxonomic history of the common powdery mildew of Chrysanthemum × morifolium (chrysanthemum, florist’s daisy), originally described in Germany as Oidium chrysanthemi, is discussed. The position of O. chrysanthemi was investigated on the basis of morphological traits and molecular phylogenetic analyses. Based on the results of this study, this species, which is closely related to Golovinomyces artemisae, was reassessed and reallocated to Golovinomyces. The phylogenetic analysis and taxonomic reassessment of the chrysanthemum powdery mildew is supplemented by a morphological description, a summary of its worldwide distribution data, and a brief discussion of the introduction of this fungus to North America. G. chrysanthemi differs from true G. artemisiae in that it has much longer conidiophores, is not constricted at the base, and has much larger and most importantly longer conidia. The close affinity of Golovinomyces to Artemisia and Chrysanthemum species signifies a coevolutionary event between the powdery mildews concerned and their host species in the subtribe Artemisiinae (Asteraceae tribe Anthemideae). This conclusion is fully supported by the current phylogeny and taxonomy of the host plant genera and the coevolution that occurred with the host and pathogen. The following powdery mildew species, which are associated with hosts belonging to the tribe Anthemideae of the Asteraceae, are epitypified: Alphitomorpha depressa β artemisiae (≡ Alphitomorpha artemisiae), Erysiphe artemisiae, and Oidium chrysanthemi. Erysiphe macrocarpa is neotypified. Their sequences were retrieved from the epitype collections and have been added to the phylogenetic tree. Golovinomyces orontii, an additional powdery mildew species on Chrysanthemum ×morifolium, is reported. This species is rarely found as a spontaneous infection and was obtained from inoculation experiments.

Endangered by laws: potential consequences of regulations against thistles on bumblebee conservation

SummaryMany bumblebee (Bombus) species are undergoing a strong decline in Europe due to, amongst other things, a decrease of food resources. While leguminous plants (Fabaceae) are considered to be one of the main pollen sources of bumblebees, thistles (Asteraceae tribe Cardueae) have been suggested to be important for male diet. Yet, several European countries apply strict regulations against thistles since they are considered to be one of the principal weeds in agricultural landscapes. Such regulations could impact bumblebee conservation through disruption of male diet and ecology. Here, we assess the male-depending importance of thistles for bumblebee species based on field observations across countries where a legal regulation against thistles is in effect. We ultimately aim to evaluate the potential consequences of these regulations on bumblebee conservation. Our results confirm that most floral visit observations of males occur on thistles (mainly Cirsium spp. and Carduus spp.) and some species are almost exclusively observed on them. Thistle removal is thus most likely a threat for bumblebees. Therefore, we advocate repealing the thistle removal acts to make way for alternative thistle regulations which reconcile biodiversity conservation and agricultural requirements.

Specialist bees collect Asteraceae pollen by distinctive abdominal drumming (Osmia) or tapping (Melissodes, Svastra)

Four species of western US Osmia (3 Cephalosmia) that are Asteraceae specialists (mesoleges) were observed using a stereotypical means of collecting pollen—abdominal drumming—to gather pollen from 21 flowering species representing nine tribes of Asteraceae. Abdominal drumming is a rapid dorso-ventral motion of the female’s abdomen (467 pats/min) used to directly collect and place pollen in the bee’s ventral scopa. A co-occurring generalist, O. lignaria, never drummed Asteraceae flowers for pollen, but instead used its legs to harvest pollen. Observed drumming by several other osmiines is noted. A different pollen-harvesting behavior, abdominal tapping, is described for two eucerine bees (Melissodes agilis and Svastra obliqua), both oligolectic for the Asteraceae. The behavior also involves a dorso-ventral motion, but they tap their distal abdominal venter against disk flowers at a slower tempo (304 taps/min). These females’ distal sternites have distinctly dense and long hair brushes for acquiring pollen by this behavior. Brief accounts of similar abdominal pollen gathering behaviors by other megachilids are summarized.

Unique Style Morphology in the Monotypic Famatinanthoideae-Famatinantheae, a Recently Established Subfamily and Tribe of Asteraceae

Abstract Famatinanthus, a recently established monotypic genus, has a unique style type with a cobblestone-like surface. These cobblestonelike units comprise several epidermal cells that often have periclinal walls, resulting in a partially “double epidermis.” The particular epidermis supports the exclusion from the genus Aphyllocladus (based on morphological data) as well as the elevation of the genus Famatinanthus to tribe and subfamily rank (based on chloroplast DNA data). To demonstrate the uniqueness of the stylar morphology of Famatinanthus, its styles and those of the remaining four species of Aphyllocladus were studied by SEM and histological sections. In addition, representatives of the basal tribes that share non-stylar characters with Famatinanthus, namely Gochnatieae, Hyalideae, Onoserideae, and Stifftieae, were studied in comparison. Due to the lack of stylar hairs, Famatinanthus is clearly distinct from Aphyllocladus, Onoseris (Onoserideae), and Hyaloseris (Stifftieae), which have stylar hai...

DNA content in species of Vernonia and Vernonanthura from South America: An approach to systematics and evolution of the Vernonieae (Asteraceae)

There are relatively few studies of DNA content in the Vernonieae (Asteraceae) tribe. The first studies were realized in the Lessingianthus genus and determined the DNA content of 25 species. After DNA content, ploidy level and the total karyotype were compared in 6 Chrysolaena species. The aim of this study was to present, for the first time, the DNA content values of Vernonanthura and Vernonia and to thereby expand knowledge of the Vernonieae tribe. A total of 19 natural populations belonging to the genera Vernonanthura and Vernonia were studied for the first time. The results were compared with other Vernonieae genera and with other Asteraceae tribes. Our results found that Vernonieae have the smallest range of 1C value variation in Asteraceae. Furthermore, there were differences in the DNA content of Vernonia and Vernonanthura. These results show that low DNA content and herbaceous habit in Vernonia are characters derived from the higher DNA content and woody habit present in Vernonanthura. These results could indicate a hybrid origin of one species and allow the determination of both the ploidy and chromosome number of other taxa. The results observed in Vernonanthura species showed a highly significant correlation between 1C-value and latitude.

Origins and recent radiation of Brazilian Eupatorieae (Asteraceae) in the eastern Cerrado and Atlantic Forest

The remarkable diversity of Eupatorieae in the Brazilian flora has received little study, despite the tribe’s very high levels of endemism and importance in the threatened Cerrado and the Atlantic Forest biodiversity hotspots. Eupatorieae are one of the largest tribes in Asteraceae with 14 of 19 recognized subtribes occurring in Brazil. We constructed the largest phylogeny of Brazilian Eupatorieae to date that sampled the nrITS and ETS, chloroplast ndhI and ndhF genes, and the ndhI–ndhG intergenic spacer for 183 species representing 77 of the 85 Brazilian genera of the tribe. Maximum likelihood and Bayesian phylogenetic analyses showed that these species are not collectively monophyletic, so their distribution reflects multiple introductions into Brazil. A novel clade was found that includes 75% of the genera endemic to Brazil (Cerrado-Atlantic Forest Eupatorieae, “CAFE” clade). This radiation of at least 247 species concentrated in the Cerrado and Atlantic Forest biomes of central eastern Brazil is <7 my old and exhibits several ecologically diverse life forms. Eight subtribes of Brazilian Eupatorieae (Ageratinae, Alomiinae, Ayapaninae, Critoniinae, Disynaphiinae, Eupatoriinae, Gyptidinae and Hebecliniinae) and 16 genera (Ageratum, Agrianthus, Austroeupatorium, Bejaranoa, Chromolaena, Critonia, Disynaphia, Grazielia, Hatschbachiella, Heterocondylus, Koanophyllon, Lasiolaena, Neocabreria, Praxelis, Stylotrichium, and Symphyopappus) were found to be polyphyletic. We attribute incongruities between the molecular phylogenetic results and the current classification of the tribe mostly to convergent evolution of morphological characters traditionally used in the classification of the tribe. We used these phylogenetic results to suggest changes to the classification of some subtribes and genera of Eupatorieae that occur in Brazil.

Diversity of styles and mechanisms of secondary pollen presentation in basal Asteraceae—New insights in phylogeny and function

Based on new studies on style morphology of basal subfamilies and tribes of Asteraceae (Barnadesioideae, Famatinanthoideae, Mutisioideae, Stifftioideae, Wunderlichioideae, Gochnatioideae, Hecastocleidoideae), we establish 15 style types in view of shape, bifurcation and distribution of stylar hairs and stigmatic tissue. From the stylar characters and observing different anthetic stages of the proterandrous flowers, we inferred the mechanisms of secondary pollen presentation. The high diversity of stylar shapes in the basal groups of Asteraceae is remarkable. In the most basal subfamily Barnadesioideae, the stylar surface is smooth or, at most, papillate and secondary pollen presentation is either a deposition/primitive brushing or a pump mechanism. Considering Calyceraceae (deposition mechanism) as sister group, we conclude that presumably a deposition/primitive brushing mechanism is the beginning of all secondary pollen presentations in Asteraceae. Whereas in the higher Asteraceae both the brushing and pump mechanisms function perfectly, in some lower Asteraceae, the mechanisms work less efficiently regarding pollen release. The subfamily Mutisioideae is well-defined by the occurrence of true stylar hairs and the tribe Mutisieae by its stigmatic tissue on the margins of the stylar arms, confluent at their tips. The early step from a continuous stigma covering the whole inner surface of the stylar branches (as in most basal members) to a stigma arrangement in two separate lines (as in most Asteroideae) is realized in two ways: either by adhesion of the median ventral tissues of the stylar branches (e.g. Onoseris, Wunderlichia) or by receptivity loss of the median tissues (e.g. Mutisia). Our study supports further DNA-based clades by style morphology (e.g. Famatinanthoideae).

(Un)targeted metabolomics in Asteraceae: probing the applicability of essential-oil profiles of senecio L. (Senecioneae) taxa in chemotaxonomy.

The possible applicability of (un)targeted metabolomics (volatile metabolites) for revealing taxonomic/evolutionary relationships among Senecio L. species (Asteraceae; tribe Senecioneae) was explored. Essential-oil compositional data of selected Senecio/Senecioneae/Asteraceae taxa (93 samples in total) were mutually compared by means of multivariate statistical analysis (MVA), i.e., agglomerative hierarchical clustering and principal component analysis. The MVA input data set included the very first compositional data on the essential oil extracted from the aerial parts of S. viscosus L. as well as on four different Serbian populations of S. vernalis Waldst. & Kit. (oils from aerial parts and roots; eight samples in total). This metabolomic screening of Senecio/Senecioneae/Asteraceae species (herein presented results and data from the literature) pointed to short-chain alk-1-enes (e.g., oct-1-ene, non-1-ene, and undec-1-ene), with up to now restricted general occurrence in Plantae, as characteristic chemotaxonomic markers/targets for future metabolomic studies of Senecio/Senecioneae taxa. The MVA additionally showed that the evolution of the terpene metabolism (volatile mono- and sesquiterpenoids) within the Asteraceae tribe Senecioneae was not genera specific. However, the MVA did confirm plant-organ specific production/accumulation of volatiles within S. vernalis and suggested the existence of at least two volatile chemotypes for this species.

Complete chloroplast genome sequences of Praxelis (Eupatorium catarium Veldkamp), an important invasive species

Praxelis (Eupatorium catarium Veldkamp) is a new hazardous invasive plant species that has caused serious economic losses and environmental damage in the Northern hemisphere tropical and subtropical regions. Although previous studies focused on detecting the biological characteristics of this plant to prevent its expansion, little effort has been made to understand the impact of Praxelis on the ecosystem in an evolutionary process. The genetic information of Praxelis is required for further phylogenetic identification and evolutionary studies. Here, we report the complete Praxelis chloroplast (cp) genome sequence. The Praxelis chloroplast genome is 151,410bp in length including a small single-copy region (18,547bp) and a large single-copy region (85,311bp) separated by a pair of inverted repeats (IRs; 23,776bp). The genome contains 85 unique and 18 duplicated genes in the IR region. The gene content and organization are similar to other Asteraceae tribe cp genomes. We also analyzed the whole cp genome sequence, repeat structure, codon usage, contraction of the IR and gene structure/organization features between native and invasive Asteraceae plants, in order to understand the evolution of organelle genomes between native and invasive Asteraceae. Comparative analysis identified the 14 markers containing greater than 2% parsimony-informative characters, indicating that they are potential informative markers for barcoding and phylogenetic analysis. Moreover, a sister relationship between Praxelis and seven other species in Asteraceae was found based on phylogenetic analysis of 28 protein-coding sequences. Complete cp genome information is useful for plant phylogenetic and evolutionary studies within this invasive species and also within the Asteraceae family.

Structure and chemical content of the trichomes in two Doronicum species (Asteraceae)

Non-glandular and three types of glandular trichomes localized on a peduncle and the phyllaries of two species (Doronicum orientale and D. macrophyllum) belonging to Senecioneae tribe of Asteraceae were studied by light and electron microscopy, as well as on histochemistry. The plant species differ on the trichome morphology, anatomy and arrangement. Three types of the glandular trichomes are formed on the vegetative and reproductive organs in D. orientale, whereas only one type exists in D. macrophyllum. It was shown by fluorescent microscopy and histochemistry that the phenolic substances, terpenoids and sesquiterpene lactones present in the glandular trichomes. The received results allow assuming that secretion of the trichomes is a chemical barrier to insects and fungi.

Detection of Pharmacological Active Compounds of the Asteraceae Family and their Chemotaxonomical Implications

It can be assumed that sesquiterpene lactones and natural phytosteroids (ecdysones) are the characteristic compounds of the plants from the Asteraceae family. They display certain pharmacological properties and thus are helpful in chemical descriptions of the Asteraceae tribes, subtribes and species. Also some phenolic glycosides found in genus Klasea Cass, and in genus Centaurea L. may be of medical and chemotaxonomical significance. Our studies on the species of the aforementioned taxons and the isolation of several compounds allowed for interesting conclusions of phytochemical and taxonomical nature.

Diversity of non-glandular trichomes in subtribe Lychnophorinae (Asteraceae: Vernonieae) and taxonomic implications

Vernonieae is one of the major tribes in Asteraceae (subfamily Cichorioideae) with ca. 1,100 species placed into 129 genera. Currently, 21 subtribes are recognized in Vernonieae and one of them is Lychnophorinae, almost entirely endemic to Brazil, containing 11 genera and ca. 100 species. About 42 % of Lychnophorinae genera are monophyletic, reflecting the poorly understood relationships among the members of the group. Trichomes are one of the most useful anatomical characters to be used in angiosperm taxonomy; they are diverse, exist in many taxa and are not difficult to study. This work intends to illustrate non-glandular leaf trichome diversity in Lychnophorinae and discuss this diversity in the light of the subtribe’s taxonomy. Sampled material included 67 species of 11 genera. Macerations and free hand sections were performed to be analyzed in the light microscope and photographed. A phenogram was generated using a matrix with 67 terminals (species) and 18 characters coded as binary. The subtribe Lychnophorinae displays a great diversity of non-glandular trichomes (5 types and 18 subtypes). The present study reveals the great diversity of non-glandular trichomes in Lychnophorinae. While trichome complement is of little use to distinguish genera, it appears to be a valuable characteristic at a lower taxonomic level to identify closely morphologically related species.

Sesquiterpenoids in subtribe Centaureinae (Cass.) Dumort (tribe Cardueae, Asteraceae): Distribution, 13C NMR spectral data and biological properties

Asteraceae Bercht. & J. Presl is one of the biggest and most economically important plant families. The taxonomy and phylogeny of Asteraceae is rather complex and according to the latest and most reliable taxonomic classification of Panero & Funk, based on the analysis of nine chloroplast regions, the family is divided into 12 subfamilies and 35 tribes. One of the largest tribes of Asteraceae is Cardueae Cass. with four subtribes (Carlininae, Echinopinae, Carduinae and Centaureinae) and more than 2500 species. Susanna & Garcia-Jacas have organized the genera of Centaureinae (about 800 species) into seven informal groups, which recent molecular studies have confirmed: 1. Basal genera; 2. Volutaria group; 3. Rhaponticum group; 4. Serratula group; 5. Carthamus group; 6. Crocodylium group; 7. Centaurea group. This review summarizes reports on sesquiterpenoids from the Centaureinae subtribe of the Asteraceae family, as well as the (13)C NMR spectral data described in the literature. It further reviews studies concerning the biological activities of these metabolites. For this work, literature data on sesquiterpenes from the Centaureinae subtribe were retrieved with the help of the SciFinder database and other similar data banks. All entries from 1958 until the end of 2011 were considered. This review is addressed to scientists working in the metabolomics field such as chemists, botanists, etc., the spectroscopic data reported make this work a good tool for structural elucidation, the biological section gives useful information to those who wish to study the structure activity relationships.

Host range and potential distribution of Aceria thalgi (Acari: Eriophyidae): a biological control agent for Sonchus species

AbstractSowthistles, Sonchus arvensis, S. asper and S. oleraceus (Asteraceae), are serious weeds that impact on crop production in many regions of the world. A recently described eriophyid mite, Aceria thalgi from Sonchus species found in southern Australia, was assessed for its potential as a biological control agent for these weeds. Glasshouse host range testing and field observations of 11 species from seven genera from the Lactuceae tribe of Asteraceae showed that A. thalgi survived only on plants within the Sonchinae subtribe (S. asper, S. oleraceus and S. hydrophilus) and not on the closely related Actites megalocarpus, Reichardia tingitana or other test plants. Under glasshouse conditions and varying plant ages, A. thalgi infestation caused significant growth reduction of the exotic species S. oleraceus (up to 97%) and, to a lesser extent, the Australian native S. hydrophilus (up to 33%). Six temperatures from 9.1 to 33.7°C were used to determine population growth parameters for A. thalgi. The range of temperatures suitable for population growth was used to modify a CLIMEX model based on its host S. oleraceus. The projected world distribution of the CLIMEX model indicates that the mite could establish in some areas of North America, making it a possibility for an augmentative approach to biological control of Sonchus spp. in that region. The model confirms the potential for a widespread distribution of A. thalgi in southern Australia where it could be considered for a conservative approach to biological control of Sonchus spp. in cropping systems.

Surface microstructures of daisy florets (Asteraceae) and characterization of their anisotropic wetting

The surface microstructures on ray florets of 62 species were characterized and compared with modern phylogenetic data of species affiliation in Asteraceae to determine sculptural patterns and their occurrence in the tribes of Asteraceae. Their wettability was studied to identify structural-induced droplet adhesion, which can be used for the development of artificial surfaces for water harvesting and passive surface water transport. The wettability was characterized by contact angle (CA) and tilt angle measurements, performed on fresh ray florets and their epoxy resin replica. The CAs on ray florets varied between 104° and 156°, but water droplets did not roll off when surface was tilted at 90°. Elongated cell structures and cuticle folding orientated in the same direction as the cell elongation caused capillary forces, leading to anisotropic wetting, with extension of water droplets along the length axis of epidermis cells. The strongest elongation of the droplets was also supported by a parallel, cell-overlapping cuticle striation. In artificial surfaces made of epoxy replica of ray florets, this effect was enhanced. The distribution of the identified four structural types exhibits a strong phylogenetic signal and allows the inference of an evolutionary trend in the modification of floret epidermal cells.

TAS3 genes for small ta-siARF RNAs in plants belonging to subtribe senecioninae: Occurrence of prematurely terminated RNA precursors

The various classes of plant 21- to 24-nt siRNAs derive from long dsRNA precursors that are processed by the ribonuclease Dicer-like (DCL). The species of ta-siRNA were originally discovered in Arabidopsis thaliana. Four gene families have been identified in Arabidopsis that each produces a number of ta-siRNAs: TAS1, TAS2, TAS3 and TAS4. The TAS3 genes encode ta-siR-ARF species which target the mRNA of three Auxin Response Factor (ARF) genes (ARF2, ARF3/ETT and ARF4) for subsequent degradation. The function of TAS3 precursor RNA is controlled by two miR390 target sites flanking tandem of ta-siARF sequences. In this paper, we have studied the presence of ta-siARF RNA genes in the representatives of subtribe Senecioninae. Senecioninae is the largest tribe of Asteraceae, comprised of ca. 150 genera and 3000 species which include many common succulents of greenhouses. Approximately one-third of species are placed in genus Senecio, making it one of the largest genera of flowering plants. However, there was no information on the structure of TAS genes in these plants. We revealed that the TAS3 species (TAS3-Sen1) in Senecio representatives was actively transcribed, and its homologues are distributed among many Asteracea plants and found to be similar to Arabidopsis AtTAS3a gene. We revealed several prematurely terminated transcripts of TAS3-Sen1. Finding the alternative shortened transcripts of TAS3-Sen1 lacking the 3′-terminal site cleaved by miR390 and retaining the 5′-terminal miR390 non-cleaved site suggested their using as decoys for the modulation of miR390 activity to regulate synthesis of ta-siARF RNAs in different Senecioninae species.

Adaptive evolution of the chrysanthemyl diphosphate synthase gene involved in irregular monoterpene metabolism

BackgroundChrysanthemyl diphosphate synthase (CDS) is a key enzyme in biosynthetic pathways producing pyrethrins and irregular monoterpenes. These compounds are confined to plants of the tribe Anthemideae of the Asteraceae, and play an important role in defending the plants against herbivorous insects. It has been proposed that the CDS genes arose from duplication of the farnesyl diphosphate synthase (FDS) gene and have different function from FDSs. However, the duplication time toward the origin of CDS and the evolutionary force behind the functional divergence of the CDS gene are still unknown.ResultsTwo duplication events were detected in the evolutionary history of the FDS gene family in the Asteraceae, and the second duplication led to the origin of CDS. CDS occurred after the divergence of the tribe Mutisieae from other tribes of Asteraceae but before the birth of the Anthemideae tribe. After its origin, CDS accumulated four mutations in sites homologous to the substrate-binding and catalysis sites of FDS. Of these, two sites were involved in the binding of the nucleophilic substrate isopentenyl diphosphate in FDS. Maximum likelihood analyses showed that some sites in CDS were under positive selection and were scattered throughout primary sequences, whereas in the three-dimensional structure model they clustered in the large central cavity.ConclusionPositive selection associated with gene duplication played a major role in the evolution of CDS.

Self-organizing maps of molecular descriptors for sesquiterpene lactones and their application to the chemotaxonomy of the Asteraceae family.

The Asteraceae, one of the largest families among angiosperms, is chemically characterised by the production of sesquiterpene lactones (SLs). A total of 1,111 SLs, which were extracted from 658 species, 161 genera, 63 subtribes and 15 tribes of Asteraceae, were represented and registered in two dimensions in the SISTEMATX, an in-house software system, and were associated with their botanical sources. The respective 11 block of descriptors: Constitutional, Functional groups, BCUT, Atom-centred, 2D autocorrelations, Topological, Geometrical, RDF, 3D-MoRSE, GETAWAY and WHIM were used as input data to separate the botanical occurrences through self-organising maps. Maps that were generated with each descriptor divided the Asteraceae tribes, with total index values between 66.7% and 83.6%. The analysis of the results shows evident similarities among the Heliantheae, Helenieae and Eupatorieae tribes as well as between the Anthemideae and Inuleae tribes. Those observations are in agreement with systematic classifications that were proposed by Bremer, which use mainly morphological and molecular data, therefore chemical markers partially corroborate with these classifications. The results demonstrate that the atom-centred and RDF descriptors can be used as a tool for taxonomic classification in low hierarchical levels, such as tribes. Descriptors obtained through fragments or by the two-dimensional representation of the SL structures were sufficient to obtain significant results, and better results were not achieved by using descriptors derived from three-dimensional representations of SLs. Such models based on physico-chemical properties can project new design SLs, similar structures from literature or even unreported structures in two-dimensional chemical space. Therefore, the generated SOMs can predict the most probable tribe where a biologically active molecule can be found according Bremer classification.