EggLib: processing, analysis and simulation tools for population genetics and genomics

<p>Abstract</p> <p>Background</p> <p>With the considerable growth of available nucleotide sequence data over the last decade, integrated and flexible analytical tools have become a necessity. In particular, in the field of population genetics, there is a strong need for automated and reliable procedures to conduct repeatable and rapid polymorphism analyses, coalescent simulations, data manipulation and estimation of demographic parameters under a variety of scenarios.</p> <p>Results</p> <p>In this context, we present EggLib (Evolutionary Genetics and Genomics Library), a flexible and powerful C++/Python software package providing efficient and easy to use computational tools for sequence data management and extensive population genetic analyses on nucleotide sequence data. EggLib is a multifaceted project involving several integrated modules: an underlying computationally efficient C++ library (which can be used independently in pure C++ applications); two C++ programs; a Python package providing, among other features, a high level Python interface to the C++ library; and the <monospace>egglib </monospace>script which provides direct access to pre-programmed Python applications.</p> <p>Conclusions</p> <p>EggLib has been designed aiming to be both efficient and easy to use. A wide array of methods are implemented, including file format conversion, sequence alignment edition, coalescent simulations, neutrality tests and estimation of demographic parameters by Approximate Bayesian Computation (ABC). Classes implementing different demographic scenarios for ABC analyses can easily be developed by the user and included to the package. EggLib source code is distributed freely under the GNU General Public License (GPL) from its website <url>http://egglib.sourceforge.net/</url> where a full documentation and a manual can also be found and downloaded.</p

De novo sequence assembly and characterization of the floral transcriptome in cross- and self-fertilizing plants

<p>Abstract</p> <p>Background</p> <p>The shift from cross-fertilization to predominant self-fertilization is among the most common evolutionary transitions in the reproductive biology of flowering plants. Increased inbreeding has important consequences for floral morphology, population genetic structure and genome evolution. The transition to selfing is usually characterized by a marked reduction in flower size and the loss of traits involved in pollinator attraction and the avoidance of self-fertilization. Here, we use short-read sequencing to assemble, <it>de novo</it>, the floral transcriptomes of three genotypes of <it>Eichhornia paniculata</it>, including an outcrosser and two genotypes from independently derived selfers, and a single genotype of the sister species <it>E. paradoxa</it>. By sequencing mRNA from tissues sampled at various stages of flower development, our goal was to sequence and assemble the floral transcriptome and identify differential patterns of gene expression.</p> <p>Results</p> <p>Our 24 Mbp assembly resulted in ~27,000 contigs that averaged ~900 bp in length. All four genotypes had highly correlated gene expression, but the three <it>E. paniculata </it>genotypes were more correlated with one another than each was to <it>E. paradoxa</it>. Our analysis identified 269 genes associated with floral development, 22 of which were differentially expressed in selfing lineages relative to the outcrosser. Many of the differentially expressed genes affect floral traits commonly altered in selfing plants and these represent a set of potential candidate genes for investigating the evolution of the selfing syndrome.</p> <p>Conclusions</p> <p>Our study is among the first to demonstrate the use of Illumina short read sequencing for <it>de novo </it>transcriptome assembly in non-model species, and the first to implement this technology for comparing floral transcriptomes in outcrossing and selfing plants.</p

Electrochemical ruthenium-catalysed C–H activation in water through heterogenization of a molecular catalyst

Efficient catalytic oxidative C–H activation of organic substrates remains an important challenge in synthetic chemistry. Here, we show that the combination of a transition metal catalyst, surface immobilisation and an electrochemical potential provide a promising approach to effecting these transformations in aqueous solution. A ruthenium-based molecular catalyst [Ru(tpy)(pic-PO3H2)(Cl)] (where tpy is 2,2′:6′,2′′-terpyridine, pic-PO3H2 is 4-phosphonopyrid-2-ylcarboxylic acid) was synthesised and fully characterised. Oxidation of benzyl alcohol with the catalyst in aqueous media using ceric ammonium nitrate as terminal oxidant resulted in a rapid deactivation of the catalyst. Immobilisation of the catalyst on a mesoporous indium tin oxide electrode surface through the phosphonate anchoring group was shown to circumvent the issues observed in solution. Using the heterogeneous catalyst system, the oxidation of a variety of organic substrates with varying bond dissociation energies was demonstrated with turnover numbers of up to 346. Finally, surface-analysis of the functionalised electrodes after catalysis revealed that fragmentation of the complex during the reaction was the limiting factor for catalytic performance

Harnessing non-stoichiometry and disorder in thermoelectric materials

Thermoelectric materials require an exquisite balancing of thermal and electronic transport properties. Core to achieving such a balance in thermoelectric materials is the pursuit of non-stoichiometric compositions. Non-stoichiometry serves to control the charge carrier concentration, alter the electronic structure, control electron and phonon scattering, and produce anomalies in the phononic structure. As such, the optimized material is far removed from the original parent compound. Looking to the future, a deeper understanding of non-stoichiometry and its impact on electronic and phononic transport is critical to designing the next generation of thermoelectric materials. To convey the importance of non-stoichiometry in thermoelectric materials, we will begin with two classic case examples that highlight how non-stoichiometry profoundly alters transport in thermoelectric materials. These include (i) the alteration of the electronic structure through resonant states in PbTe and (ii) alteration to phonon transport via ‘rattling’ modes in skutterudite compounds. With this foundation, we discuss our recent efforts to control transport in pnictide and chalcogenide compounds through a combination of first principles calculations of defect structures, combinatorial growth of alloys, and bulk synthesis. For example, Figure 1 highlights how first principles calculations can offer insight into native defect populations and their impact on electronic structure. Strategies to accelerate discovery in this high dimensional phase space and critical challenges that remain serve to conclude this discussion of thermoelectric materials. Please click Additional Files below to see the full abstract

Amount of Information Needed for Model Choice in Approximate Bayesian Computation

Approximate Bayesian Computation (ABC) has become a popular technique in evolutionary genetics for elucidating population structure and history due to its flexibility. The statistical inference framework has benefited from significant progress in recent years. In population genetics, however, its outcome depends heavily on the amount of information in the dataset, whether that be the level of genetic variation or the number of samples and loci. Here we look at the power to reject a simple constant population size coalescent model in favor of a bottleneck model in datasets of varying quality. Not only is this power dependent on the number of samples and loci, but it also depends strongly on the level of nucleotide diversity in the observed dataset. Whilst overall model choice in an ABC setting is fairly powerful and quite conservative with regard to false positives, detecting weaker bottlenecks is problematic in smaller or less genetically diverse datasets and limits the inferences possible in non-model organism where the amount of information regarding the two models is often limited. Our results show it is important to consider these limitations when performing an ABC analysis and that studies should perform simulations based on the size and nature of the dataset in order to fully assess the power of the study

Melting as a String-Mediated Phase Transition

We present a theory of the melting of elemental solids as a dislocation-mediated phase transition. We model dislocations near melt as non-interacting closed strings on a lattice. In this framework we derive simple expressions for the melting temperature and latent heat of fusion that depend on the dislocation density at melt. We use experimental data for more than half the elements in the Periodic Table to determine the dislocation density from both relations. Melting temperatures yield a dislocation density of (0.61\pm 0.20) b^{-2}, in good agreement with the density obtained from latent heats, (0.66\pm 0.11) b^{-2}, where b is the length of the smallest perfect-dislocation Burgers vector. Melting corresponds to the situation where, on average, half of the atoms are within a dislocation core.Comment: 18 pages, LaTeX, 3 eps figures, to appear in Phys. Rev.

Complex patterns of local adaptation in teosinte

Populations of widely distributed species often encounter and adapt to specific environmental conditions. However, comprehensive characterization of the genetic basis of adaptation is demanding, requiring genome-wide genotype data, multiple sampled populations, and a good understanding of population structure. We have used environmental and high-density genotype data to describe the genetic basis of local adaptation in 21 populations of teosinte, the wild ancestor of maize. We found that altitude, dispersal events and admixture among subspecies formed a complex hierarchical genetic structure within teosinte. Patterns of linkage disequilibrium revealed four mega-base scale inversions that segregated among populations and had altitudinal clines. Based on patterns of differentiation and correlation with environmental variation, inversions and nongenic regions play an important role in local adaptation of teosinte. Further, we note that strongly differentiated individual populations can bias the identification of adaptive loci. The role of inversions in local adaptation has been predicted by theory and requires attention as genome-wide data become available for additional plant species. These results also suggest a potentially important role for noncoding variation, especially in large plant genomes in which the gene space represents a fraction of the entire genome

The Carboxy-Terminal Domain of Dictyostelium C-Module-Binding Factor Is an Independent Gene Regulatory Entity

The C-module-binding factor (CbfA) is a multidomain protein that belongs to the family of jumonji-type (JmjC) transcription regulators. In the social amoeba Dictyostelium discoideum, CbfA regulates gene expression during the unicellular growth phase and multicellular development. CbfA and a related D. discoideum CbfA-like protein, CbfB, share a paralogous domain arrangement that includes the JmjC domain, presumably a chromatin-remodeling activity, and two zinc finger-like (ZF) motifs. On the other hand, the CbfA and CbfB proteins have completely different carboxy-terminal domains, suggesting that the plasticity of such domains may have contributed to the adaptation of the CbfA-like transcription factors to the rapid genome evolution in the dictyostelid clade. To support this hypothesis we performed DNA microarray and real-time RT-PCR measurements and found that CbfA regulates at least 160 genes during the vegetative growth of D. discoideum cells. Functional annotation of these genes revealed that CbfA predominantly controls the expression of gene products involved in housekeeping functions, such as carbohydrate, purine nucleoside/nucleotide, and amino acid metabolism. The CbfA protein displays two different mechanisms of gene regulation. The expression of one set of CbfA-dependent genes requires at least the JmjC/ZF domain of the CbfA protein and thus may depend on chromatin modulation. Regulation of the larger group of genes, however, does not depend on the entire CbfA protein and requires only the carboxy-terminal domain of CbfA (CbfA-CTD). An AT-hook motif located in CbfA-CTD, which is known to mediate DNA binding to A+T-rich sequences in vitro, contributed to CbfA-CTD-dependent gene regulatory functions in vivo