Genome-wide Association Mapping Approach Research Articles

Marker-trait association analysis for easy fruit destemming and mechanical harvestability traits in New Mexican chile pepper (Capsicum annuum L.)

IntroductionChile pepper (Capsicum annuum L.) mechanization is a promising alternative to traditional hand harvesting due to the costs associated with manual harvest, as well as the increasing unavailability of skilled manual chile harvesters. This study aimed to identify single nucleotide polymorphisms (SNPs) associated with mechanical harvestability (MH) and yield-related traits using multi-locus genome-wide association mapping approaches in a C. annuum association mapping population.MethodsA C. annuum association mapping panel for mechanical harvest was manually direct seeded in an augmented block design in two locations. After filtration, imputation, and quality control 27,291 single nucleotide polymorphism (SNP) markers were used for association analyses. Six multi-locus GWAS models were implemented to identify marker trait association.Results and DiscussionMulti-locus GWAS models identified 12 major SNP markers (R2 > 10) across nine chromosomes associated with plant architecture, easy destemming traits, and yield parameters. The presence of a major QTL in chromosome P2, dstem2.1, identified recently to be associated with destemming force, was confirmed. Mature green and mature red yield shared three SNP markers mapped on chromosome P3, P5, and P6 explaining 11.94% to 25.15% of the phenotypic variation. Candidate gene analysis for the significant loci identified 19 candidate genes regulating different phytohormone biosynthesis/signaling, metabolic processes, transcription, methylation, DNA repair/replication, and RNA splicing, with potential roles in controlling plant architecture and morphology. The diverse positions of the associated SNPs suggest the complex nature of these quantitative traits, involvement of multiple genetic factors, and novel significant marker-trait associations. Results from this study will be relevant for genetic improvement of mechanical harvestability traits in New Mexican chile pepper using molecular markerassisted breeding and selection.

Mapping of flumioxazin tolerance in a snap bean diversity panel leads to the discovery of a master genomic region controlling multiple stress resistance genes.

Effective weed management tools are crucial for maintaining the profitable production of snap bean (Phaseolus vulgaris L.). Preemergence herbicides help the crop to gain a size advantage over the weeds, but the few preemergence herbicides registered in snap bean have poor waterhemp (Amaranthus tuberculatus) control, a major pest in snap bean production. Waterhemp and other difficult-to-control weeds can be managed by flumioxazin, an herbicide that inhibits protoporphyrinogen oxidase (PPO). However, there is limited knowledge about crop tolerance to this herbicide. We aimed to quantify the degree of snap bean tolerance to flumioxazin and explore the underlying mechanisms. We investigated the genetic basis of herbicide tolerance using genome-wide association mapping approach utilizing field-collected data from a snap bean diversity panel, combined with gene expression data of cultivars with contrasting response. The response to a preemergence application of flumioxazin was measured by assessing plant population density and shoot biomass variables. Snap bean tolerance to flumioxazin is associated with a single genomic location in chromosome 02. Tolerance is influenced by several factors, including those that are indirectly affected by seed size/weight and those that directly impact the herbicide's metabolism and protect the cell from reactive oxygen species-induced damage. Transcriptional profiling and co-expression network analysis identified biological pathways likely involved in flumioxazin tolerance, including oxidoreductase processes and programmed cell death. Transcriptional regulation of genes involved in those processes is possibly orchestrated by a transcription factor located in the region identified in the GWAS analysis. Several entries belonging to the Romano class, including Bush Romano 350, Roma II, and Romano Purpiat presented high levels of tolerance in this study. The alleles identified in the diversity panel that condition snap bean tolerance to flumioxazin shed light on a novel mechanism of herbicide tolerance and can be used in crop improvement.

Breeding and genomics approaches for improving phosphorus-use efficiency in grain legumes

Phosphorus (P) is an essential plant macronutrient, but P sources for plant growth are non-renewable, causing great concern for future sustainable agriculture and global food security. Thus, enhancing plant P-use efficiency (PUE) by improving P-acquisition and P-utilization efficiencies is urgently needed in various crops, including grain legumes, for intensive cropping systems. This review discusses how to harness the genetic variability in PUE traits across grain legume gene pools to improve PUE using various conventional breeding approaches and emerging breeding tools. The genetic architecture of PUE traits is complex, being quantitatively inherited and highly influenced by the environment. Thus, we discuss how the biparental QTL mapping approach has been used to dissect the genetic architecture of PUE traits. Unprecedented advances in legume genomics resources, especially high-throughput single nucleotide polymorphisms, have facilitated uncovering genomic regions related to PUE across the whole genome using a genome-wide association mapping approach. Likewise, the availability of complete genome sequence information, pangenome sequences, and the whole-genome resequencing approach have provided novel insights into structural variation, including presence/absence and copy number variations, underpinning PUE. Simultaneously, progress in functional genomics, including transcriptomics and computational biology, has facilitated the discovery of various underlying transcription factors and the corresponding downstream P signal perception genes and candidate gene(s) controlling PUE and conferring low-P tolerance in various legumes with putative function. We also discuss updated metabolomics and proteomics approaches that have improved our understanding of various gene networks, P-starvation signaling pathways, and P acquisition and utilization of molecular mechanisms important for PUE. Finally, we summarize how novel breeding schemes, including genomic selection, speed breeding, and emerging CRISPR/Cas9-based genome editing tools, will assist in designing P-use-efficient cultivars and adapting grain legumes to low-P environments. Thus, enhancing PUE by integrating various ‘omics’ approaches could improve P-acquisition and P-utilization efficiencies in various modern grain legume cultivars grown in intensive cropping systems to restrict P-fertilizer overuse and preserve the declining non-renewable global rock phosphate reservoir for securing an economical and sustainable future agriculture. • Phosphorus (P) is one of the most essential nutrients required for plant growth and development. • P fertilizers being non-renewable, judicious utilization of P fertilizer is urgently needed for sustaining legume yield for ensuring global food security. • Plants have evolved several molecular, physiological and biochemical mechanisms to sense, acquire and utilize soil P and adapt under P impoverished environments. • ‘Omics’ approach could greatly assist in unraveling the underlying genomic regions with their function contributing to improving phosphorus use efficiency in legume crops.

Novel Genes and Genetic Loci Associated With Root Morphological Traits, Phosphorus-Acquisition Efficiency and Phosphorus-Use Efficiency in Chickpea.

Chickpea—the second most important grain legume worldwide—is cultivated mainly on marginal soils. Phosphorus (P) deficiency often restricts chickpea yields. Understanding the genetics of traits encoding P-acquisition efficiency and P-use efficiency will help develop strategies to reduce P-fertilizer application. A genome-wide association mapping approach was used to determine loci and genes associated with root architecture, root traits associated with P-acquisition efficiency and P-use efficiency, and any associated proxy traits. Using three statistical models—a generalized linear model (GLM), a mixed linear model (MLM), and a fixed and random model circulating probability unification (FarmCPU) —10, 51, and 40 marker-trait associations (MTAs), respectively were identified. A single nucleotide polymorphism (SNP) locus (Ca1_12310101) on Ca1 associated with three traits, i.e., physiological P-use efficiency, shoot dry weight, and shoot P content was identified. Genes related to shoot P concentration (NAD kinase 2, dynamin-related protein 1C), physiological P-use efficiency (fasciclin-like arabinogalactan protein), specific root length (4-coumarate–CoA ligase 1) and manganese concentration in mature leaves (ABC1 family protein) were identified. The MTAs and novel genes identified in this study can be used to improve P-use efficiency in chickpea.

Genome-Wide Association Analyses Reveal Genomic Regions Controlling Canopy Wilting in Soybean.

Drought stress causes the greatest soybean [Glycine max (L.) Merr.] yield losses among the abiotic stresses in rain-fed U.S. growing areas. Because less than 10% of U.S. soybean hectares are irrigated, combating this stress requires soybean plants which possess physiological mechanisms to tolerate drought for a period of time. Phenotyping for these mechanisms is challenging, and the genetic architecture for these traits is poorly understood. A morphological trait, slow or delayed canopy wilting, has been observed in a few exotic plant introductions (PIs), and may lead to yield improvement in drought stressed fields. In this study, we visually scored wilting during stress for a panel of 162 genetically diverse maturity group VI-VIII soybean lines genotyped with the SoySNP50K iSelect BeadChip. Field evaluation of canopy wilting was conducted under rain-fed conditions at two locations (Athens, GA and Salina, KS) in 2015 and 2016. Substantial variation in canopy wilting was observed among the genotypes. Using a genome-wide association mapping approach, 45 unique SNPs that tagged 44 loci were associated with canopy wilting in at least one environment with one region identified in a single environment and data from across all environments. Several new soybean accessions were identified with canopy wilting superior to those of check genotypes. The germplasm and genomic regions identified can be used to better understand the slow canopy wilting trait and be incorporated into elite germplasm to improve drought tolerance in soybean.

Genomic Regions Associated with Virulence in Pyrenophora teres f. teres Identified by Genome-Wide Association Analysis and Biparental Mapping.

Net form net blotch (NFNB), caused by the fungal pathogen Pyrenophora teres f. teres, is an important foliar disease present in all barley-producing regions of the world. This fungus is a hemibiotrophic and heterothallic ascomycete, where sexual recombination can lead to changes in disease expression in the host. Knowledge of the genetic architecture and genes involved in virulence is vital to increase the durability of NFNB resistance in barley cultivars. We used a genome-wide association mapping approach to characterize P. teres f. teres genomic regions associated with virulence in Australian barley cultivars. One hundred eighty-eight P. teres f. teres isolates collected across five Australian states were genotyped using Diversity Arrays Technology sequence markers and phenotyped across 20 different barley genotypes. Association mapping identified 14 different genomic regions associated with virulence, with the majority located on P. teres f. teres chromosomes 3 and 5 and one each present on chromosomes 1, 6, and 9. Four of the regions identified were confirmed by quantitative trait loci (QTL) mapping. The QTL regions are discussed in the context of their genomic architecture together with examination of their gene contents, which identified 20 predicted effectors. The number of QTL shown in this study at the population level clearly illustrates a complex genetic basis of P. teres f. teres virulence compared with pure necrotrophs, such as the wheat pathogens Parastagonospora nodorum and Parastagonospora tritici-repentis.

Charcot-Marie-Tooth type 4B2 demyelinating neuropathy in miniature Schnauzer dogs caused by a novel splicing SBF2 (MTMR13) genetic variant: a new spontaneous clinical model.

BackgroundCharcot-Marie-Tooth (CMT) disease is the most common neuromuscular disorder in humans affecting 40 out of 100,000 individuals. In 2008, we described the clinical, electrophysiological and pathological findings of a demyelinating motor and sensory neuropathy in Miniature Schnauzer dogs, with a suspected autosomal recessive mode of inheritance based on pedigree analysis. The discovery of additional cases has followed this work and led to a genome-wide association mapping approach to search for the underlying genetic cause of the disease.MethodsFor genome wide association screening, genomic DNA samples from affected and unaffected dogs were genotyped using the Illumina CanineHD SNP genotyping array. SBF2 and its variant were sequenced using primers and PCRs. RNA was extracted from muscle of an unaffected and an affected dog and RT-PCR performed. Immunohistochemistry for myelin basic protein was performed on peripheral nerve section specimens.ResultsThe genome-wide association study gave an indicative signal on canine chromosome 21. Although the signal was not of genome-wide significance due to the small number of cases, the SBF2 (also known as MTMR13) gene within the region of shared case homozygosity was a strong positional candidate, as 22 genetic variants in the gene have been associated with demyelinating forms of Charcot-Marie-Tooth disease in humans. Sequencing of SBF2 in cases revealed a splice donor site genetic variant, resulting in cryptic splicing and predicted early termination of the protein based on RNA sequencing results.ConclusionsThis study reports the first genetic variant in Miniature Schnauzer dogs responsible for the occurrence of a demyelinating peripheral neuropathy with abnormally folded myelin. This discovery establishes a genotype/phenotype correlation in affected Miniature Schnauzers that can be used for the diagnosis of these dogs. It further supports the dog as a natural model of a human disease; in this instance, Charcot-Marie-Tooth disease. It opens avenues to search the biological mechanisms responsible for the disease and to test new therapies in a non-rodent large animal model. In particular, recent gene editing methods that led to the restoration of dystrophin expression in a canine model of muscular dystrophy could be applied to other canine models such as this before translation to humans.

Candidate genes and genome-wide association study of grain protein content and protein deviation in durum wheat.

Stable QTL for grain protein content co-migrating with nitrogen-related genes have been identified by the candidate genes and genome-wide association mapping approaches useful for marker-assisted selection. Grain protein content (GPC) is one of the most important quality traits in wheat, defining the nutritional and end-use properties and rheological characteristics. Over the years, a number of breeding programs have been developed aimed to improving GPC, most of them having been prevented by the negative correlation with grain yield. To overcome this issue, a collection of durum wheat germplasm was evaluated for both GPC and grain protein deviation (GPD) in seven field trials. Fourteen candidate genes involved in several processes related to nitrogen metabolism were precisely located on two high-density consensus maps of common and durum wheat, and six of them were found to be highly associated with both traits. The wheat collection was genotyped using the 90K iSelect array, and 11 stable quantitative trait loci (QTL) for GPC were detected in at least three environments and the mean across environments by the genome-wide association mapping. Interestingly, seven QTL were co-migrating with N-related candidate genes. Four QTL were found to be significantly associated to increases of GPD, indicating that selecting for GPC could not affect final grain yield per spike. The combined approaches of candidate genes and genome-wide association mapping led to a better understanding of the genetic relationships between grain storage proteins and grain yield per spike, and provided useful information for marker-assisted selection programs.

Unravelling the genomic architecture of bull fertility in Holstein cattle.

BackgroundFertility is considered an important economic trait in dairy cattle. Most studies have investigated cow fertility while bull fertility has received much less consideration. The main objective of this study was to perform a comprehensive genomic analysis in order to unravel the genomic architecture underlying sire fertility in Holstein dairy cattle. The analysis included the application of alternative genome-wide association mapping approaches and the subsequent use of diverse gene set enrichment tools.ResultsThe association analyses identified at least eight genomic regions strongly associated with bull fertility. Most of these regions harbor genes, such as KAT8, CKB, TDRD9 and IGF1R, with functions related to sperm biology, including sperm development, motility and sperm-egg interaction. Moreover, the gene set analyses revealed many significant functional terms, including fertilization, sperm motility, calcium channel regulation, and SNARE proteins. Most of these terms are directly implicated in sperm physiology and male fertility.ConclusionsThis study contributes to the identification of genetic variants and biological processes underlying sire fertility. These findings can provide opportunities for improving bull fertility via marker-assisted selection.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-016-0454-6) contains supplementary material, which is available to authorized users.

Quantitative disease resistance to the bacterial pathogen Xanthomonas campestris involves an Arabidopsis immune receptor pair and a gene of unknown function.

Although quantitative disease resistance (QDR) is a durable and broad-spectrum form of resistance in plants, the identification of the genes underlying QDR is still in its infancy. RKS1 (Resistance related KinaSe1) has been reported recently to confer QDR in Arabidopsis thaliana to most but not all races of the bacterial pathogen Xanthomonas campestris pv. campestris (Xcc). We therefore explored the genetic bases of QDR in A. thaliana to diverse races of X. campestris (Xc). A nested genome-wide association mapping approach was used to finely map the genomic regions associated with QDR to Xcc12824 (race 2) and XccCFBP6943 (race 6). To identify the gene(s) implicated in QDR, insertional mutants (T-DNA) were selected for the candidate genes and phenotyped in response to Xc. We identified two major QTLs that confer resistance specifically to Xcc12824 and XccCFBP6943. Although QDR to Xcc12824 is conferred by At5g22540 encoding for a protein of unknown function, QDR to XccCFBP6943 involves the well-known immune receptor pair RRS1/RPS4. In addition to RKS1, this study reveals that three genes are involved in resistance to Xc with strikingly different ranges of specificity, suggesting that QDR to Xc involves a complex network integrating multiple response pathways triggered by distinct pathogen molecular determinants.

The genetics of intra‐ and interspecific competitive response and effect in a local population of an annual plant species

Summary While competition is recognized as a major factor responsible for plant community dynamics, the genetics of intra‐ and interspecific competitive ability of a target species (i.e. level of intra‐population genetic variation, identity of phenotypic traits under selection and genetic bases) still deserves a deeper investigation at the local spatial scale by considering both numerous genotypes and several interacting species. In this study, we tested whether the genetics of competitive response and effect in Arabidopsis thaliana was dependent on the competitive environment at both the intraspecific and interspecific levels. We used a mapping population of 48 accessions (i) that maximize the genetic diversity of a local population of A. thaliana and (ii) that have been genotyped for 168 503 single nucleotide polymorphisms. In a common garden experiment, those 48 accessions were grown in six competitive environments: the absence of competition, intraspecific competition and interspecific competition with four species frequently associated with A. thaliana in natural plant communities (i.e. Poa annua, Stellaria media, Trifolium repens and Veronica arvensis). A suite of nine phenotypic traits, including a proxy of fitness, were scored on each target A. thaliana plant and the above‐ground dry biomass of its corresponding competitor was estimated. We first showed that crossing reaction norms of competitive response (A. thaliana performance) and effect (competitor biomass) might promote maintenance of genetic variation in a local population of A. thaliana and species coexistence at a fine spatial scale. By estimating genotypic gradients of selection, we then demonstrated that the optimal phenotypic strategies in response to competition depend on the identity of the competitor species. Finally, a genomewide association mapping approach highlighted that genomic regions associated with direct genetic effects were (i) dependent on the competitor species and (ii) different from genomic regions associated with interspecific indirect genetic effects. While a first step, this study highlighted the power of adding ecology to genomics in A. thaliana to identify genetic bases underlying micro‐geographic adaptation to competition. Next‐generation sequencing technologies will undoubtedly facilitate the discovery of molecular and genetic mechanisms underlying competitive ability in other plant species, and thereby the prediction of evolutionary trajectories of plant communities.

Linkage disequilibrium and genome-wide association analysis for anthocyanin pigmentation and fruit color in eggplant.

BackgroundThe genome-wide association (GWA) approach represents an alternative to biparental linkage mapping for determining the genetic basis of trait variation. Both approaches rely on recombination to re-arrange the genome, and seek to establish correlations between phenotype and genotype. The major advantages of GWA lie in being able to sample a much wider range of the phenotypic and genotypic variation present, in being able to exploit multiple rounds of historical recombination in many different lineages and to include multiple accessions of direct relevance to crop improvement.ResultsA 191 accessions eggplant (Solanum melongena L.) association panel, comprising a mixture of breeding lines, old varieties and landrace selections originating from Asia and the Mediterranean Basin, was SNP genotyped and scored for anthocyanin pigmentation and fruit color at two locations over two years. The panel formed two major clusters, reflecting geographical provenance and fruit type. The global level of linkage disequilibrium was 3.4 cM. A mixed linear model appeared to be the most appropriate for GWA. A set of 56 SNP locus/phenotype associations was identified and the genomic regions harboring these loci were distributed over nine of the 12 eggplant chromosomes. The associations were compared with the location of known QTL for the same traits.ConclusionThe GWA mapping approach was effective in validating a number of established QTL and, thanks to the wide diversity captured by the panel, was able to detect a series of novel marker/trait associations.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-896) contains supplementary material, which is available to authorized users.

Species- and genome-wide dissection of the shoot ionome in Brassica napus and its relationship to seedling development.

Knowing the genetic basis of the plant ionome is essential for understanding the control of nutrient transport and accumulation. The aim of this research was to (i) study mineral nutrient concentrations in a large and diverse set of Brassica napus, (ii) describe the relationships between the shoot ionome and seedling development, and (iii) identify genetic regions associated with variation of the shoot ionome. The plant material under study was a germplasm set consisting of 509 inbred lines that was genotyped by a 6K single nucleotide polymorphism (SNP) array and phenotyped by analyzing the concentrations of eleven mineral nutrients in the shoots of 30 days old seedlings. Among mineral concentrations, positive correlations were found, whereas mineral concentrations were mainly negatively correlated with seedling development traits from earlier studies. In a genome-wide association mapping approach, altogether 29 significantly associated loci were identified across seven traits after correcting for multiple testing. The associations included a locus with effects on the concentrations of Cu, Mn, and Zn on chromosome C3, and a genetic region with multiple associations for Na concentration on chromosome A9. This region was situated within an association hotspot close to SOS1, a key gene for Na tolerance in plants.

Genome wide association mapping to identify aluminium tolerance loci in bread wheat

Aluminium (Al) toxicity in acid soils continues to be a major concern for crop production, especially for wheat which is a moderately tolerant cereal crop species. So far, Al tolerance was known to be controlled by few genetic loci detected clearly by classical mapping studies. Here, we report the outcome of a genome wide association mapping approach in bread wheat (Triticum aestivum L.) using 525 Diversity Array Technology markers genotyped in a core collection of 96 winter wheat accessions. Marker-trait associations (MTAs) were detected using both general linear model (GLM) and mixed linear model (MLM). Five significant MTAs were identified as shared by models on chromosomes 1A, 1D, 3B and 6A. Highly significant MTAs were identified by MLM on chromosomes 1D and 3B which could be new candidate loci for future studies. Some of our results are in line with prior reports, but some appear to be novel. Potential candidate genes have been searched in respective chromosomal bins for highly significant MTAs detected by MLM. The loci identified in our study have the potential to improve Al tolerance in wheat and hence need to be verified and utilized for breeding tolerant cultivars worldwide.

Precision phenotyping of biomass accumulation in triticale reveals temporal genetic patterns of regulation

To extend agricultural productivity by knowledge-based breeding and tailor varieties adapted to specific environmental conditions, it is imperative to improve our ability to assess the dynamic changes of the phenome of crops under field conditions. To this end, we have developed a precision phenotyping platform that combines various sensors for a non-invasive, high-throughput and high-dimensional phenotyping of small grain cereals. This platform yielded high prediction accuracies and heritabilities for biomass of triticale. Genetic variation for biomass accumulation was dissected with 647 doubled haploid lines derived from four families. Employing a genome-wide association mapping approach, two major quantitative trait loci (QTL) for biomass were identified and the genetic architecture of biomass accumulation was found to be characterized by dynamic temporal patterns. Our findings highlight the potential of precision phenotyping to assess the dynamic genetics of complex traits, especially those not amenable to traditional phenotyping.

Admixture mapping identifies a locus on 6q25 associated with breast cancer risk in US Latinas

Among US Latinas and Mexican women, those with higher European ancestry have increased risk of breast cancer. We combined an admixture mapping and genome-wide association mapping approach to search for genomic regions that may explain this observation. Latina women with breast cancer (n= 1497) and Latina controls (n= 1272) were genotyped using Affymetrix and Illumina arrays. We inferred locus-specific genetic ancestry and compared the ancestry between cases and controls. We also performed single nucleotide polymorphism (SNP) association analyses in regions of interest. Correction for multiple-hypothesis testing was conducted using permutations (P(corrected)). We identified one region where genetic ancestry was significantly associated with breast cancer risk: 6q25 [odds ratio (OR) per Indigenous American chromosome 0.75, 95% confidence interval (CI): 0.65-0.85, P= 1.1 × 10(-5), P(corrected)= 0.02]. A second region on 11p15 showed a trend towards association (OR per Indigenous American chromosome 0.77, 95% CI: 0.68-0.87, P= 4.3 × 10(-5), P(corrected)= 0.08). In both regions, breast cancer risk decreased with higher Indigenous American ancestry in concordance with observations made on global ancestry. The peak of the 6q25 signal includes the estrogen receptor 1 (ESR1) gene and 5' region, a locus previously implicated in breast cancer. Genome-wide association analysis found that a multi-SNP model explained the admixture signal in both regions. Our results confirm that the association between genetic ancestry and breast cancer risk in US Latinas is partly due to genetic differences between populations of European and Indigenous Americans origin. Fine-mapping within the 6q25 and possibly the 11p15 loci will lead to the discovery of the biologically functional variant/s behind this association.

Identification of marker-trait associations in the German winter barley breeding gene pool (Hordeum vulgare L.)

A genome-wide association mapping approach for grain yield and traits of high agronomic relevance was carried out on basis of a set of 61 six-rowed and 48 two-rowed German winter barley (Hordeum vulgare L.) cultivars representing breeding progress in the period 1959–2003. Extensive phenotyping was conducted in field trials carried out at 12 locations in 3 years. Heritability was estimated at between 0.45 for grain yield and 0.94 for grains per spike. By using the Illumina Golden Gate Bead Array technology, 833 single nucleotide polymorphisms with an allele frequency higher than 5% were obtained. Linkage disequilibrium on the whole genome extends to 7.35 cM. Based on a mixed linear model approach taking into account the population structure estimated on the basis of 72 simple sequence repeat markers covering the whole barley genome, 91 significant marker-trait associations were detected, corresponding to 48 different genomic regions.

Association mapping for Fusarium head blight resistance in European soft winter wheat

Resistance to Fusarium head blight (FHB) is of great importance in wheat breeding programs in the northern hemisphere. In Europe, breeders prefer adapted germplasm as resistance donor because of high grain yield and quality demands. Our objective was to identify chromosomal regions affecting FHB resistance among 455 European soft winter wheat (Triticum aestivum L.) lines using a genome-wide association mapping approach and to analyze the importance of epistatic interactions. All entries were evaluated for FHB resistance by inoculation in two environments and several ratings. Wheat was genotyped by 115 simple sequence repeat markers randomly distributed across the genome and two allele-specific markers for Rht-B1 and Rht-D1 genes. The genome-wide scan revealed nine significant (P < 0.05) marker–phenotype associations on seven chromosomes including dwarfing gene Rht-D1. Using a Bonferroni–Holm correction, three significant associations remained on chromosomes 1B, 1D, and 2D. The proportion of the genotypic variance explained simultaneously by individual markers was 36% and increased to 50% when two digenic epistatic interactions were considered, one of them associated with Rht-B1. In conclusion, new genomic regions on chromosomes 1D and 3A could be found for FHB resistance in European wheat and the effect of epistatic interactions was substantial.

Candidate gene association resource (CARe): design, methods, and proof of concept.

The National Heart, Lung, and Blood Institute's Candidate Gene Association Resource (CARe), a planned cross-cohort analysis of genetic variation in cardiovascular, pulmonary, hematologic, and sleep-related traits, comprises >40,000 participants representing 4 ethnic groups in 9 community-based cohorts. The goals of CARe include the discovery of new variants associated with traits using a candidate gene approach and the discovery of new variants using the genome-wide association mapping approach specifically in African Americans. CARe has assembled DNA samples for >40,000 individuals self-identified as European American, African American, Hispanic, or Chinese American, with accompanying data on hundreds of phenotypes that have been standardized and deposited in the CARe Phenotype Database. All participants were genotyped for 7 single-nucleotide polymorphisms (SNPs) selected based on prior association evidence. We performed association analyses relating each of these SNPs to lipid traits, stratified by sex and ethnicity, and adjusted for age and age squared. In at least 2 of the ethnic groups, SNPs near CETP, LIPC, and LPL strongly replicated for association with high-density lipoprotein cholesterol concentrations, PCSK9 with low-density lipoprotein cholesterol levels, and LPL and APOA5 with serum triglycerides. Notably, some SNPs showed varying effect sizes and significance of association in different ethnic groups. The CARe Pilot Study validates the operational framework for phenotype collection, SNP genotyping, and analytic pipeline of the CARe project and validates the planned candidate gene study of approximately 2000 biological candidate loci in all participants and genome-wide association study in approximately 8000 African American participants. CARe will serve as a valuable resource for the scientific community.