The carbon dioxide chaperon efficiency for the reaction H + O2 + M yields HO2 + M from ignition delay times behind reflected shock waves

Ignition delay times for stoichiometric hydrogen-oxygen in argon with and without carbon dioxide were measured behind reflected shock waves. A 20-reaction kinetic mechanism models the measured hydrogen-oxygen delay times over the temperature range 950 to 1300 K. The chaperon efficiency for carbon dioxide determined for the hydrogen-oxygen carbon dioxide mixture was 7.0. This value is in agreement with literature values but much less than a recent value obtained from flow tube experiments. Delay times measured behind a reflected shock wave were about 20% longer than those measured behind incident shock waves. The kinetic mechanism successfully modeled the high-pressure data of Skinner and the hydrogen-air data of Stack. It is suggested that the lowest temperature points for the hydrogen-air data of Slack are unreliable and that the 0.27-atm data may illustrate a case where vibrational relaxation of nitrogen is important. The reaction pathway HO2 yields H2O2 yields OH yields H was required to model the high-pressure data of Skinner. The successful modeling of the stoichiometric hydrogen-air data demonstrates the appropriateness of deriving kinetic models from data for gas mixtures highly diluted with argon. The technique of reducing a detailed kinetic mechanism to only the important reactions for a limited range of experimental data may render the mechanism useless for other test conditions

Hydrogen oxidation mechanism with applications to (1) the chaperon efficiency of carbon dioxide and (2) vitiated air testing

Ignition delay times for the hydrogen/oxygen/carbon dioxide/argon system were obtained behind reflected shock waves. A detailed kinetic mechanism modeled the experimental hydrogen/oxygen data, Skinner and Ringrose's high-pressure data, and Slack and Grillo's hydrogen/air data. A carbon dioxide chaperon efficiency of 7.0 +/- 0.2 was determined. The reaction pathway H2O yields H2O2 yields OH yields H was required to model the high-pressure data. It is suggested that some of the lowest temperature data points (1.0 and 0.5 atm) for Slack and Grillo's hydrogen/air experiments are in error. It was found that the technique of simplifying a detailed kinetic mechanism for a limited range of experimental data may render the model useless for other test conditions

Analysis of the recombination landscape of hexaploid bread wheat reveals genes controlling recombination and gene conversion frequency

Background: Sequence exchange between homologous chromosomes through crossing over and gene conversion is highly conserved among eukaryotes, contributing to genome stability and genetic diversity. A lack of recombination limits breeding efforts in crops; therefore, increasing recombination rates can reduce linkage drag and generate new genetic combinations. Results: We use computational analysis of 13 recombinant inbred mapping populations to assess crossover and gene conversion frequency in the hexaploid genome of wheat (Triticum aestivum). We observe that high-frequency crossover sites are shared between populations and that closely related parents lead to populations with more similar crossover patterns. We demonstrate that gene conversion is more prevalent and covers more of the genome in wheat than in other plants, making it a critical process in the generation of new haplotypes, particularly in centromeric regions where crossovers are rare. We identify quantitative trait loci for altered gene conversion and crossover frequency and confirm functionality for a novel RecQ helicase gene that belongs to an ancient clade that is missing in some plant lineages including Arabidopsis. Conclusions: This is the first gene to be demonstrated to be involved in gene conversion in wheat. Harnessing the RecQ helicase has the potential to break linkage drag utilizing widespread gene conversions

A high-throughput delayed fluorescence method reveals underlying differences in the control of circadian rhythms in Triticum aestivum and Brassica napus

Additional file 16. Wheat cultivars (Fig. 6)

Limited haplotype diversity underlies polygenic trait architecture across 70 years of wheat breeding

Background Selection has dramatically shaped genetic and phenotypic variation in bread wheat. We can assess the genomic basis of historical phenotypic changes, and the potential for future improvement, using experimental populations that attempt to undo selection through the randomizing effects of recombination. Results We bred the NIAB Diverse MAGIC multi-parent population comprising over 500 recombinant inbred lines, descended from sixteen historical UK bread wheat varieties released between 1935 and 2004. We sequence the founders’ genes and promoters by capture, and the MAGIC population by low-coverage whole-genome sequencing. We impute 1.1 M high-quality SNPs that are over 99% concordant with array genotypes. Imputation accuracy only marginally improves when including the founders’ genomes as a haplotype reference panel. Despite capturing 73% of global wheat genetic polymorphism, 83% of genes cluster into no more than three haplotypes. We phenotype 47 agronomic traits over 2 years and map 136 genome-wide significant associations, concentrated at 42 genetic loci with large and often pleiotropic effects. Around half of these overlap known quantitative trait loci. Most traits exhibit extensive polygenicity, as revealed by multi-locus shrinkage modelling. Conclusions Our results are consistent with a gene pool of low haplotypic diversity, containing few novel loci of large effect. Most past, and projected future, phenotypic changes arising from existing variation involve fine-scale shuffling of a few haplotypes to recombine dozens of polygenic alleles of small effect. Moreover, extensive pleiotropy means selection on one trait will have unintended consequences, exemplified by the negative trade-off between yield and protein content, unless selection and recombination can break unfavorable trait-trait associations

Harnessing genetic potential of wheat germplasm banks through impact-oriented-prebreeding for future food and nutritional security

The value of exotic wheat genetic resources for accelerating grain yield gains is largely unproven and unrealized. We used next-generation sequencing, together with multi-environment phenotyping, to study the contribution of exotic genomes to 984 three-way-cross-derived (exotic/elite1//elite2) pre-breeding lines (PBLs). Genomic characterization of these lines with haplotype map-based and SNP marker approaches revealed exotic specific imprints of 16.1 to 25.1%, which compares to theoretical expectation of 25%. A rare and favorable haplotype (GT) with 0.4% frequency in gene bank identified on chromosome 6D minimized grain yield (GY) loss under heat stress without GY penalty under irrigated conditions. More specifically, the ‘T’ allele of the haplotype GT originated in Aegilops tauschii and was absent in all elite lines used in study. In silico analysis of the SNP showed hits with a candidate gene coding for isoflavone reductase IRL-like protein in Ae. tauschii. Rare haplotypes were also identified on chromosomes 1A, 6A and 2B effective against abiotic/biotic stresses. Results demonstrate positive contributions of exotic germplasm to PBLs derived from crosses of exotics with CIMMYT’s best elite lines. This is a major impact-oriented pre-breeding effort at CIMMYT, resulting in large-scale development of PBLs for deployment in breeding programs addressing food security under climate change scenarios

Identification and characterisation of MORC6 as a component of the RNA-directed DNA methylation pathway in Arabidopsis thaliana

RNA silencing pathways control the expression of genes and other DNA loci by the action of small RNA molecules and are found in many eukaryotes. In plants there are a number of RNA silencing pathways, of which RNA-directed DNA methylation (RdDM) is one. In this pathway the small RNA molecules direct DNA methylation, resulting in the down regulation of expression of the target locus. In terms of the mechanism of the pathway it is mostly well characterised but several gaps exist in our knowledge. These relate to its initiation, where it is not known how RdDM targets the correct locus; methylation, where it is unclear how the action of small RNAs triggers methylation; and chromatin modification, where it is unclear how methylated DNA is converted into higher order chromatin modification. These gaps in the pathway raised the possibility of the involvement of novel proteins and so this project aimed to identify and characterise mutants in these proteins. Screening of a library of putative RdDM mutants in Arabidopsis thaliana identified three alleles in MORC6, which encodes a GHKL ATPase containing protein associated with RdDM that is thought to form higher order chromatin in response to DNA methylation. Analysis of the three alleles revealed that morc6 mutants have no effect on siRNA production but at certain loci do have an effect on DNA methylation and so would suggest that MORC6 is also involved in the DNA methylation process in RdDM at specific loci. It was also shown that silencing by RdDM can still occur in morc6 mutants in a limited capacity and that this silencing is stochastic and cell autonomous in nature. These findings point to MORC6 also having further roles in RdDM other than higher order chromatin modification and so increase our understanding of the mechanism of RdDM

Prospects for the use of biological control agents against Anoplophora in Europe

This review summarises the literature on biocontrol of Anoplophora spp. and discusses which are the strongest candidates for use in Europe. Some of the methods could be useful for control, but are unlikely to be instrumental in achieving eradication. \u2022 Entomopathogenic fungi: Could be used as biopesticides as fungal infection results in high mortality rates and has already been developed into a commercial product in Japan for Anoplophora control. \u2022 Parasitic nematodes: Potential for use as biopesticides due to high mortality rates and effective application methods have already been developed. Steinernema feltiae and S. carpocapsae, are authorised for use in Europe. \u2022 Parasitoids: A previously uncharacterised parasitoid of A. chinensis, Aprostocetus anoplophorae Delvare (Hymenoptera: Eulophidae), was identified in Italy in 2002 and it has been shown to be capable of parasitizing up to 72% of A. chinensis eggs. Some native European parasitoid species (e.g. Spathius erythrocephalus) have potential to be used as a biocontrol. \u2022 Predators: Two woodpecker species that are native to Europe (Dendrocopos major and Picus canus) have been shown to be effective at controlling A. glabripennis numbers in Chinese forests. \u2022 Pathogenic bacteria: Are currently not a strong prospect for use in biocontrol with no study yet advancing to field trials