Flowering time is a complex trait that controls adaptation of plants to their local environment in the outcrossing species Zea mays (maize). We dissected variation for flowering time with a set of 5000 recombinant inbred lines (maize Nested Association Mapping population, NAM). Nearly a million plants were assayed in eight environments but showed no evidence for any single large-effect quantitative trait loci (QTLs). Instead, we identified evidence for numerous small-effect QTLs shared among families; however, allelic effects differ across founder lines. We identified no individual QTLs at which allelic effects are determined by geographic origin or large effects for epistasis or environmental interactions. Thus, a simple additive model accurately predicts flowering time for maize, in contrast to the genetic architecture observed in the selfing plant species rice and Arabidopsis.
Maize genetic diversity has been used to understand the molecular basis of phenotypic variation and to improve agricultural efficiency and sustainability. We crossed 25 diverse inbred maize lines to the B73 reference line, capturing a total of 136,000 recombination events. Variation for recombination frequencies was observed among families, influenced by local (cis) genetic variation. We identified evidence for numerous minor single-locus effects but little two-locus linkage disequilibrium or segregation distortion, which indicated a limited role for genes with large effects and epistatic interactions on fitness. We observed excess residual heterozygosity in pericentromeric regions, which suggested that selection in inbred lines has been less efficient in these regions because of reduced recombination frequency. This implies that pericentromeric regions may contribute disproportionally to heterosis.
Trypsin and mast cell tryptase cleave proteinase-activated receptor 2 and, by unknown mechanisms, induce widespread inflammation. We found that a large proportion of primary spinal afferent neurons, which express proteinase-activated receptor 2, also contain the proinflammatory neuropeptides calcitonin gene-related peptide and substance P. Trypsin and tryptase directly signal to neurons to stimulate release of these neuropeptides, which mediate inflammatory edema induced by agonists of proteinase-activated receptor 2. This new mechanism of protease-induced neurogenic inflammation may contribute to the proinflammatory effects of mast cells in human disease. Thus, tryptase inhibitors and antagonists of proteinase-activated receptor 2 may be useful anti-inflammatory agents.
SummaryCrop improvement and the dissection of complex genetic traits require germplasm diversity. Although this necessary phenotypic variability exists in diverse maize, most research is conducted using a small subset of inbred lines. An association population of 302 lines is now available -a valuable research tool that captures a large proportion of the alleles in cultivated maize. Provided that appropriate statistical models correcting for population structure are included, this tool can be used in association analyses to provide high-resolution evaluation of multiple alleles. This study describes the population structure of the 302 lines, and investigates the relationship between population structure and various measures of phenotypic and breeding value. On average, our estimates of population structure account for 9.3% of phenotypic variation, roughly equivalent to a major quantitative trait locus (QTL), with a high of 35%. Inclusion of population structure in association models is critical to meaningful analyses. This new association population has the potential to identify QTL with small effects, which will aid in dissecting complex traits and in planning future projects to exploit the rich diversity present in maize.
BackgroundGenotyping by sequencing, a new low-cost, high-throughput sequencing technology was used to genotype 2,815 maize inbred accessions, preserved mostly at the National Plant Germplasm System in the USA. The collection includes inbred lines from breeding programs all over the world.ResultsThe method produced 681,257 single-nucleotide polymorphism (SNP) markers distributed across the entire genome, with the ability to detect rare alleles at high confidence levels. More than half of the SNPs in the collection are rare. Although most rare alleles have been incorporated into public temperate breeding programs, only a modest amount of the available diversity is present in the commercial germplasm. Analysis of genetic distances shows population stratification, including a small number of large clusters centered on key lines. Nevertheless, an average fixation index of 0.06 indicates moderate differentiation between the three major maize subpopulations. Linkage disequilibrium (LD) decays very rapidly, but the extent of LD is highly dependent on the particular group of germplasm and region of the genome. The utility of these data for performing genome-wide association studies was tested with two simply inherited traits and one complex trait. We identified trait associations at SNPs very close to known candidate genes for kernel color, sweet corn, and flowering time; however, results suggest that more SNPs are needed to better explore the genetic architecture of complex traits.ConclusionsThe genotypic information described here allows this publicly available panel to be exploited by researchers facing the challenges of sustainable agriculture through better knowledge of the nature of genetic diversity.
Methanol synthesis by CO2 hydrogenation is attractive in view of avoiding the environmental implications associated with the production of the traditional syngas feedstock and mitigating global warming. However, there still is a lack of efficient catalysts for such alternative processes. Herein, we unveil the high activity, 100 % selectivity, and remarkable stability for 1000 h on stream of In2 O3 supported on ZrO2 under industrially relevant conditions. This strongly contrasts to the benchmark Cu-ZnO-Al2 O3 catalyst, which is unselective and experiences rapid deactivation. In-depth characterization of the In2 O3 -based materials points towards a mechanism rooted in the creation and annihilation of oxygen vacancies as active sites, whose amount can be modulated in situ by co-feeding CO and boosted through electronic interactions with the zirconia carrier. These results constitute a promising basis for the design of a prospective technology for sustainable methanol production.
Breeding to increase beta-carotene levels in cereal grains, termed provitamin A biofortification, is an economical approach to address dietary vitamin A deficiency in the developing world. Experimental evidence from association and linkage populations in maize (Zea mays L.) demonstrate that the gene encoding beta-carotene hydroxylase 1 (crtRB1) underlies a principal quantitative trait locus associated with beta-carotene concentration and conversion in maize kernels. crtRB1 alleles associated with reduced transcript expression correlate with higher beta-carotene concentrations. Genetic variation at crtRB1 also affects hydroxylation efficiency among encoded allozymes, as observed by resultant carotenoid profiles in recombinant expression assays. The most favorable crtRB1 alleles, rare in frequency and unique to temperate germplasm, are being introgressed via inexpensive PCR marker-assisted selection into tropical maize germplasm adapted to developing countries, where it is most needed for human health.
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